Obesity in Tibetans aged 30-70 living at different altitudes under the north and south faces of Mt. Everest

Lower Prevalence of Body Fat-Defined Obesity at Higher Altitudes in Peruvian Adults

Woolcott, Orison O., Till Seuring, and Oscar A. Castillo. Lower prevalence of body fat-defined obesity at higher altitudes in Peruvian adults. High Alt Med Biol. 24:214-222, 2023. Background: Previous studies have reported a lower prevalence of obesity (defined as a body mass index [BMI] ≥30 kg/m2) in populations from higher altitudes. Since BMI does not distinguish fat mass and fat-free mass, it is unclear whether there is an inverse association between altitude and body fat-defined obesity. Methods: We performed an analysis of cross-sectional data to examine the association between altitude and body fat-defined obesity (as opposed to BMI-defined obesity) using individual-level data from a nationally representative sample of the Peruvian adult population living between 0 and 5,400 m altitude. Body fat-defined obesity was diagnosed using the relative fat mass (RFM), an anthropometric index validated to estimate whole-body fat percentage. RFM cutoffs for obesity diagnosis were ≥40% for women and ≥30% for men. We utilized Poisson regression to estimate the prevalence ratio and confidence intervals (CIs) as the measure of the association, adjusting for age, cigarette use, and diabetes. Results: Analysis comprised 36,727 individuals (median age, 39 years; 50.1% women). In rural areas, for a one-km increase in altitude, the prevalence of body fat-defined obesity decreased by 12% among women (adjusted prevalence ratio: 0.88; 95% CI, 0.86 - 0.90; p < 0.001) and 19% among men (adjusted prevalence ratio: 0.81; 95% CI, 0.77 - 0.86; p < 0.001), on average, when all the other variables were held constant. The inverse association between altitude and obesity was less strong in urban areas than in rural areas but remained significant among women (p = 0.001) and men (p < 0.001). However, the relationship between altitude and obesity in women who live in urban areas appears to be nonlinear. Conclusions: In Peruvian adults, the prevalence of body fat-defined obesity was inversely associated with altitude. Whether this inverse association is explained by altitude per se or confounded by socioeconomic or other environmental factors, or differences in race/ethnicity or lifestyle, warrants further investigation.

Somatotype altitudinal variation and its relationship with the nutritional status of children in the Jujuy province, Argentina

OBJECTIVES

To study the somatotype variations adjusted by altitude, age, sex, and BMI categories, and to assess the health status of the children population.

METHODS

A sample of 460 children aged 8-13 years was assessed in a cross-sectional study conducted on anthropometric measurements between 2011 and 2015. Data were categorized into two age groups: Group 8-10, Group 11-13 and two altitudes: Highland (>2000 masl), lowland (<2000 masl). The somatotypic profile was determined by the Heath and Carter's study method and the Body Mass Index was used to assess children nutritional status. Generalized linear latent variable models (GLLVM) were performed to test the association between somatotype and geographic altitude. Individual age-sex specific somatotypes were plotted in a two-dimension somatochart, and group dispersion was displayed by the somatotype attitudinal mean.

RESULTS

The sample has an overall endomorph-mesomorph body type, exhibiting different patterns when altitude and sex were considered. The GLLVM showed that the whole somatotype was different by altitude. Highland children occupied central to endomorphic-mesomorphic places in the somatochart with lower variation. In both altitudes, girls exhibited higher endomorphy than boys. Several discrepancies between the BMI categorization and the somatotype were observed.

CONCLUSIONS

Jujenean children show differential body patterns across geographic altitude which exhibit age and sex variations. Children have a differential tendency to a fat mass gain. The BMI showed some inconsistencies with somatotype, leading to a misclassification of the child nutritional status, this highlights the importance of not to treat the BMI in isolation but with other determinants of the health status.

Altitude and metabolic syndrome in China: Beneficial effects of healthy diet and physical activity

Background

The correlation between altitude and metabolic syndrome has not been extensively studied, and the mediation effects of diet and physical activity remain unclear. We evaluated the cross-sectional correlations between altitude and metabolic syndrome and the possible mediation effects of diet and physical activity in China.

Methods

We included 89 485 participants from the China Multi-Ethnic Cohort. We extracted their altitude information from their residential addresses and determined if they had metabolic syndrome by the presence of three or more of the following components: abdominal obesity, reduced high-density lipoprotein cholesterol (HDL-C), elevated triglycerides, elevated glucose, and high blood pressure at recruitment. We conducted multivariable logistic regression and mediation analyses for all and separately for Han ethnic participants.

Results

The participants had a mean age of 51.67 years and 60.56% were female. The risk difference of metabolic syndrome was -3.54% (95% confidence interval (CI) = -4.24, -2.86) between middle and low altitudes, -1.53% (95%CI = -2.53, -0.46) between high and low altitudes, and 2.01% (95% CI = 0.92, 3.09) between high and middle altitudes. Of the total estimated effect between middle and low altitude, the effect mediated by increased physical activity was -0.94% (95% CI = -1.04, -0.86). Compared to low altitude, the effects mediated by a healthier diet were -0.40% (95% CI = -0.47, -0.32) for middle altitude and -0.72% (95% CI = -0.87, -0.58) for high altitude. Estimates were similar in the Han ethnic group.

Conclusions

Living at middle and high altitudes was significantly associated with lower risk of metabolic syndrome compared to low altitude, with middle altitude having the lowest risk. We found mediation effects of diet and physical activity.

Factors Associated with Normal-Weight Abdominal Obesity Phenotype in a Representative Sample of the Peruvian Population: A 4-Year Pooled Cross-Sectional Study

To examine factors associated with abdominal obesity among normal-weight individuals from the Demographic and Health Survey of Peru (2018-2021). Cross-sectional analytical study. The outcome variable was abdominal obesity defined according to JIS criteria. Crude (cPR) and adjusted prevalence ratios (aPR) were estimated for the association between sociodemographic and health-related variables and abdominal obesity using the GLM Poisson distribution with robust variance estimates. A total of 32,109 subjects were included. The prevalence of abdominal obesity was 26.7%. The multivariate analysis showed a statistically significant association between abdominal obesity and female sex (aPR: 11.16; 95% CI 10.43-11.94); categorized age 35 to 59 (aPR: 1.71; 95% CI 1.65-1.78); 60 to 69 (aPR: 1.91; 95% CI 1.81-2.02); and 70 or older(aPR: 1.99; 95% CI 1.87-2.10); survey year 2019 (aPR: 1.22; 95% CI 1.15-1.28); 2020 (aPR: 1.17; 95% CI 1.11-1.24); and 2021 (aPR: 1.12; 95% CI 1.06-1.18); living in Andean region (aPR: 0.91; 95% CI 0.86-0.95); wealth index poor (aPR: 1.26; 95% CI 1.18-1.35); middle (aPR: 1.17; 95% CI 1.08-1.26); rich (aPR: 1.26; 95% CI 1.17-1.36); and richest (aPR: 1.25; 95% CI 1.16-1.36); depressive symptoms (aPR: 0.95; 95% CI 0.92-0.98); history of hypertension (aPR: 1.08; 95% CI 1.03-1.13), type 2 diabetes (aPR: 1.13; 95% CI 1.07-1.20); and fruit intake 3 or more servings/day (aPR: 0.92; 95% CI 0.89-0.96). Female sex, older ages, and low and high income levels increased the prevalence ratio for abdominal obesity, while depressive symptoms, living in the Andean region, and fruit intake of 3 or more servings/day decreased it.

The association between living altitude and serum leptin concentrations in native women

BACKGROUND

Lower diabetes prevalence and cardiovascular mortality have been observed in residents at a higher altitude. Leptin is associated with incident diabetes and adverse cardiovascular outcomes, and our aim was to investigate the association of living altitude with serum leptin concentrations.

METHODS

Two cross-sectional surveys were used in this study, including native populations living at Tibet (high altitude) and Beijing (low altitude). A propensity score was conducted for matching age and body mass index (BMI) between native women at high and low altitude. Pearson's correlation analysis was performed to evaluate the correlation of leptin with other variables.

RESULTS

A total of 1414 native women were included in this study, including 594 at high altitude and 820 at low altitude. The serum leptin concentrations of native women living at high altitude were 13.74 ± 11.03 ng/ml, which was significantly lower than that of native women living at low altitude (20.90 ± 12.91 ng/ml). After matching age and BMI, women living at the high altitude still had lower serum leptin concentrations. After adjusting for the potential confounding factors, the correlation coefficient between Ln (leptin) and BMI of women at high altitude was significantly lower than that of women at low altitude (0.228 versus 0.559; P <0.0001). The serum leptin concentrations of each BMI subgroup (<18.5, 18.5 to <25, 25 to <30, ≥ 30 kg/m²) in women at high altitude were lower than that in women at low altitude.

CONCLUSIONS

Serum leptin concentrations were significantly decreased in native women living at high altitude, and living altitude may alter the correlation of BMI and leptin. The findings of our study support that residents at high altitude have a protective effect with regards to improving cardiovascular and metabolic outcomes.

Mechanisms for Combined Hypoxic Conditioning and Divergent Exercise Modes to Regulate Inflammation, Body Composition, Appetite, and Blood Glucose Homeostasis in Overweight and Obese Adults: A Narrative Review

Obesity is a major global health issue and a primary risk factor for metabolic-related disorders. While physical inactivity is one of the main contributors to obesity, it is a modifiable risk factor with exercise training as an established non-pharmacological treatment to prevent the onset of metabolic-related disorders, including obesity. Exposure to hypoxia via normobaric hypoxia (simulated altitude via reduced inspired oxygen fraction), termed hypoxic conditioning, in combination with exercise has been increasingly shown in the last decade to enhance blood glucose regulation and decrease the body mass index, providing a feasible strategy to treat obesity. However, there is no current consensus in the literature regarding the optimal combination of exercise variables such as the mode, duration, and intensity of exercise, as well as the level of hypoxia to maximize fat loss and overall body compositional changes with hypoxic conditioning. In this narrative review, we discuss the effects of such diverse exercise and hypoxic variables on the systematic and myocellular mechanisms, along with physiological responses, implicated in the development of obesity. These include markers of appetite regulation and inflammation, body conformational changes, and blood glucose regulation. As such, we consolidate findings from human studies to provide greater clarity for implementing hypoxic conditioning with exercise as a safe, practical, and effective treatment strategy for obesity.

Hypoxia as a Double-Edged Sword to Combat Obesity and Comorbidities

The global epidemic of obesity is tightly associated with numerous comorbidities, such as type II diabetes, cardiovascular diseases and the metabolic syndrome. Among the key features of obesity, some studies have suggested the abnormal expansion of adipose-tissue-induced local endogenous hypoxic, while other studies indicated endogenous hyperoxia as the opposite trend. Endogenous hypoxic aggravates dysfunction in adipose tissue and stimulates secretion of inflammatory molecules, which contribute to obesity. In contrast, hypoxic exposure combined with training effectively generate exogenous hypoxic to reduce body weight and downregulate metabolic risks. The (patho)physiological effects in adipose tissue are distinct from those of endogenous hypoxic. We critically assess the latest advances on the molecular mediators of endogenous hypoxic that regulate the dysfunction in adipose tissue. Subsequently we propose potential therapeutic targets in adipose tissues and the small molecules that may reverse the detrimental effect of local endogenous hypoxic. More importantly, we discuss alterations of metabolic pathways in adipose tissue and the metabolic benefits brought by hypoxic exercise. In terms of therapeutic intervention, numerous approaches have been developed to treat obesity, nevertheless durability and safety remain the major concern. Thus, a combination of the therapies that suppress endogenous hypoxic with exercise plans that augment exogenous hypoxic may accelerate the development of more effective and durable medications to treat obesity and comorbidities.

An ecological study on the spatially varying association between adult obesity rates and altitude in the United States: using geographically weighted regression

In this research, we evaluated the relationship between obesity rates and altitude using a cross-county study design. We applied a geographically weighted regression (GWR) to examine the spatially varying association between adult obesity rates and altitude after adjusting for four predictor variables including physical activity. A significant negative relationship between altitude and adult obesity rates were found in the GWR model. Our GWR model fitted the data better than OLS regression (R² = 0.583), as indicated by an improved R² (average R² = 0.670; range: 0.26-0.77) and a lower Akaike Information Criteria (AIC) value (14,736.88 vs. 15,386.59 in the OLS model). These approaches, evidencing spatial varying associations, proved very useful to refine interpretations of the statistical output on adult obesity. This study underscored the geographic variation in relationships between adult obesity rates and mean county altitude in the United States. Our study confirmed a varying overall negative relationship between county-level adult obesity rates and mean county altitude after taking other confounding factors into account.

Distinct Nutrient Intake Style in Inhabitants of Ultra-High-Altitude Areas in North of Tibet, China: A Cross-Sectional Study Based on Newly Developed Tibetan Food Frequency Questionnaires

Dietary pattern is quite distinct among the inhabitants of high-altitude areas because of environmental and geographical uniqueness; hence, it is important to investigate this data as accurately as possible. However, very few data are related to these populations up to now. Based on the food frequency questionnaire (FFQ) used in the Chinese population, a revised Tibetan edition was developed with respect to the lifestyle in high-altitude areas. After assessment of validity and reproducibility, a nutrition intake survey was conducted among 1,071 randomly sampled Tibetan people. In addition, the Bland-Altman approach was used to compare the agreement between the two dietary tools. For the reproducibility analysis, intraclass correlation coefficients (ICC) were calculated to examine the agreement of food groups and nutrients from the two FFQs (FFQ1 and FFQ2). Nutrient intake was calculated using food composition tables. For the validity analysis, Pearson's correlation of food groups intakes varied from 0.22 to 0.91 (unadjusted). The correlations of nutrients ranged from 0.24 to 0.76 (unadjusted). In the analysis of reliability, the ICC of food groups varied from 0.27 to 0.70 (unadjusted). The ICC of nutrient intakes ranged from 0.22 to 0.87 (unadjusted). The results of nutritional analysis showed that ~25% of foods consumed frequently were traditional Tibetan foods. However, traditional Han foods were frequently consumed. In addition, the energy, iron, and protein intakes for male or female subjects were close to the Chinese Dietary Nutrient Reference Intake (Chinese DRIs); however, fat and sodium intakes were significantly higher than the Chinese DRIs. Interestingly, lower intakes of other types of nutrition, such as vitamin C were detected in people living in high-altitude areas. Our data indicated that excess consumption of fat and sodium and insufficient intake of vitamin C were common among Tibetan people, as compared with the most Chinese people living in the plateau areas. More investigations are needed to reveal the association between the food intake style and high-altitude endemic diseases.

Oxygen in Metabolic Dysfunction and Its Therapeutic Relevance

Significance: In recent years, a number of studies have shown altered oxygen partial pressure at a tissue level in metabolic disorders, and some researchers have considered oxygen to be a (macro) nutrient. Oxygen availability may be compromised in obesity and several other metabolism-related pathological conditions, including sleep apnea-hypopnea syndrome, the metabolic syndrome (which is a set of conditions), type 2 diabetes, cardiovascular disease, and cancer. Recent Advances: Strategies designed to reduce adiposity and its accompanying disorders have been mainly centered on nutritional interventions and physical activity programs. However, novel therapies are needed since these approaches have not been sufficient to counteract the worldwide increasing rates of metabolic disorders. In this regard, intermittent hypoxia training and hyperoxia could be potential treatments through oxygen-related adaptations. Moreover, living at a high altitude may have a protective effect against the development of abnormal metabolic conditions. In addition, oxygen delivery systems may be of therapeutic value for supplying the tissue-specific oxygen requirements. Critical Issues: Precise in vivo methods to measure oxygenation are vital to disentangle some of the controversies related to this research area. Further, it is evident that there is a growing need for novel in vitro models to study the potential pathways involved in metabolic dysfunction to find appropriate therapeutic targets. Future Directions: Based on the existing evidence, it is suggested that oxygen availability has a key role in obesity and its related comorbidities. Oxygen should be considered in relation to potential therapeutic strategies in the treatment and prevention of metabolic disorders. Antioxid. Redox Signal. 35, 642-687.

Phenotypic differences between highlanders and lowlanders in Papua New Guinea

OBJECTIVES

Altitude is one of the most demanding environmental pressures for human populations. Highlanders from Asia, America and Africa have been shown to exhibit different biological adaptations, but Oceanian populations remain understudied [Woolcock et al., 1972; Cotes et al., 1974; Senn et al., 2010]. We tested the hypothesis that highlanders phenotypically differ from lowlanders in Papua New Guinea, as a result of inhabiting the highest mountains in Oceania for at least 20,000 years.

MATERIALS AND METHODS

We collected data for 13 different phenotypes related to altitude for 162 Papua New Guineans living at high altitude (Mont Wilhelm, 2,300-2,700 m above sea level (a.s.l.) and low altitude (Daru, <100m a.s.l.). Multilinear regressions were performed to detect differences between highlanders and lowlanders for phenotypic measurements related to body proportions, pulmonary function, and the circulatory system.

RESULTS

Six phenotypes were significantly different between Papua New Guinean highlanders and lowlanders. Highlanders show shorter height (p-value = 0.001), smaller waist circumference (p-value = 0.002), larger Forced Vital Capacity (FVC) (p-value = 0.008), larger maximal (p-value = 3.20e -4) and minimal chest depth (p-value = 2.37e -5) and higher haemoglobin concentration (p-value = 3.36e -4).

DISCUSSION

Our study reports specific phenotypes in Papua New Guinean highlanders potentially related to altitude adaptation. Similar to other human groups adapted to high altitude, the evolutionary history of Papua New Guineans appears to have also followed an adaptive biological strategy for altitude.

[Into thin air - Altitude training and hypoxic conditioning: From athlete to patient]

INTRODUCTION

Hypoxic exposure should be considered as a continuum, the effects of which depend on the dose and individual response to hypoxia. Hypoxic conditioning (HC) represents an innovative and promising strategy, ranging from improved human performance to therapeutic applications.

STATE OF THE ART

With the aim of improving sports performance, the effectiveness of hypoxic exposure, whether natural or simulated, is difficult to demonstrate because of the large variability of the protocols used. In therapeutics, the benefits of HC are described in many pathological conditions such as obesity or cardiovascular pathologies. If the HC benefits from a strong preclinical rationale, its application to humans remains limited.

PERSPECTIVES

Advances in training and acclimation will require greater personalization and precise periodization of hypoxic exposures. For patients, the harmonization of HC protocols, the identification of biomarkers and the development and subsequent validation of devices allowing a precise control of the hypoxic stimulus are necessary steps for the development of HC.

CONCLUSIONS

From the athlete to the patient, HC represents an innovative and promising field of research, ranging from the improvement of human performance to the prevention and treatment of certain pathologies.

Hypoxia, energy balance, and obesity: An update

Because of the enduring rise in the prevalence of obesity worldwide, there is continued interest in hypoxia as a mechanism underlying the pathophysiology of obesity and its comorbidities and as a potential therapeutic adjunct for the management of the disease. Lifelong exposure to altitude is accompanied by a lower risk for obesity, whereas altitude sojourns are generally associated with a loss of body mass. A negative energy balance upon exposure to hypoxia can be due to a combination of changes in determinants of energy expenditure (resting metabolic rate and physical activity energy expenditure) and energy intake (appetite). Over the past 15 years, the potential therapeutic interest of hypobaric or normobaric hypoxic exposure in individuals with obesity-to lower body mass and improve health status-has become an active field of research. Various protocols have been implemented, using actual altitude sojourns or intermittent normobaric hypoxic exposures, at rest or in association with physical activity. Although several studies suggest benefits on body mass and cardiovascular and metabolic variables, further investigations are required before recommending hypoxic exposure in obesity management programs. Future studies should also better clarify the effects of hypoxia on appetite, the intestinal microbiota, and finally on overall energy balance.

Association of altitude and urbanization with hypertension and obesity: analysis of the Nepal Demographic and Health Survey 2016

BACKGROUND

Nepal's Himalayan range attracts mountaineers, climbers and tourists from all across the globe. Limited recent evidence suggests that exposure to hypoxia at a higher altitude may be a risk factor for hypertension and a protective factor for obesity. The existing urban-rural disparities in Nepal in health and economic resources may be anticipated in the burden of hypertension and obesity, two rapidly growing public health issues, but they remain largely unstudied. Therefore this study aims to assess the association of altitude and urbanization with hypertension and overweight/obesity in Nepal.

METHODS

Data on 10 473 participants from a nationally representative survey, the 2016 Nepal Demographic and Health Survey (NDHS), was used. The NDHS assessed/measured blood pressure, height, weight, urbanization and the altitude of participants' households by following standard procedures. Logistic and linear regression models were used to study the association of altitude (per 100 m increases) and urbanization with hypertension and obesity, or their continuous measurements (i.e. systolic and diastolic blood pressure [SBP and DBP, respectively] and body mass index [BMI]).

RESULTS

The prevalence of hypertension, overweight and obesity was 25.6%, 19.6% and 4.8%, respectively. After controlling for covariates, residents of metropolitan cities had a 30% higher prevalence of overweight/obesity (adjusted prevalence ratio 1.30 [95% confidence interval {CI} 1.11 to 1.52]) than their rural counterparts. For altitude, there was a marginally increased odds of hypertension and overweight/obesity with elevation. Consistently, DBP (β = 0.18 [95% CI 0.09 to 0.27]) and BMI increased with altitude (β = 0.11 [95% CI 0.08 to 0.13]).

CONCLUSION

Urbanization was positively associated with BMI, while altitude showed a marginally positive association with hypertension and overweight/obesity. Given the role of obesity and hypertension in the aetiology of other chronic diseases and subsequently associated mortality and health care costs, residents in urban areas and at higher altitudes may benefit from weight control interventions and BP monitoring, respectively.

Interpretation of maternal blood glucose during pregnancy at high altitude area, Abha-Saudi Arabia

Background and Aims:

In women who reside at high altitude, fasting plasma glucose is lower than at sea level, and further decrease of fasting blood glucose was noticed during pregnancy. This study aimed to set cutoff level of fasting plasma glucose during pregnancy at high altitude. The obtained data intended for interpretation of gestational blood sugar results and early detection of those who at risk of developing gestational diabetes.

Methods:

A cross-sectional study was conducted to determine the cutoff level of fasting plasma glucose during pregnancy at high altitude. The subjects were pregnant women who attending the routine antenatal care at Abha Maternity Hospital and Mahayil Aseer Maternity hospital. Plasma glucose concentrations and Body Mass Index (BMI), socio-demographic and obstetric data were entered into the Statistical Package for Social Sciences (SPSS) version 20. Comparison amongst these variables were carried out through t test (numerical variables) and Chi Square test (proportions). A P value of <0.05 was considered as statistically significant.

Results:

The overall results obtained indicated that the fasting plasma glucose concentrations and BMI were significantly lower (p = 0.0001) at high altitude area (Abha) than low altitude area (Mahayil Aseer). Age was the only socio-demographic factor that showed significant difference between the two groups (p-value was <0.05).

Conclusion:

Up to our knowledge, this is the first study addressing the interpretation of fasting blood glucose during pregnancy at high altitude area in Saudi Arabia. Our findings support the importance of careful interpretation of fasting blood glucose of pregnant women who reside at high altitude areas. The implementation of this policy at high altitude areas in the Kingdom of Saudi Arabia is recommended for early detection of gestational diabetes and timed intervention to avoid complications.

AMPK and the Need to Breathe and Feed: What's the Matter with Oxygen?

We live and to do so we must breathe and eat, so are we a combination of what we eat and breathe? Here, we will consider this question, and the role in this respect of the AMP-activated protein kinase (AMPK). Emerging evidence suggests that AMPK facilitates central and peripheral reflexes that coordinate breathing and oxygen supply, and contributes to the central regulation of feeding and food choice. We propose, therefore, that oxygen supply to the body is aligned with not only the quantity we eat, but also nutrient-based diet selection, and that the cell-specific expression pattern of AMPK subunit isoforms is critical to appropriate system alignment in this respect. Currently available information on how oxygen supply may be aligned with feeding and food choice, or vice versa, through our motivation to breathe and select particular nutrients is sparse, fragmented and lacks any integrated understanding. By addressing this, we aim to provide the foundations for a clinical perspective that reveals untapped potential, by highlighting how aberrant cell-specific changes in the expression of AMPK subunit isoforms could give rise, in part, to known associations between metabolic disease, such as obesity and type 2 diabetes, sleep-disordered breathing, pulmonary hypertension and acute respiratory distress syndrome.

The 2018 Global Research Expedition on Altitude Related Chronic Health (Global REACH) to Cerro de Pasco, Peru: an Experimental Overview

NEW FINDINGS

What is the central question of this study? Herein, a methodological overview of our research team's (Global REACH) latest high altitude research expedition to Peru is provided. What is the main finding and its importance? The experimental objectives, expedition organization, measurements and key cohort data are discussed. The select data presented in this manuscript demonstrate the haematological differences between lowlanders and Andeans with and without excessive erythrocytosis. The data also demonstrate that exercise capacity was similar between study groups at high altitude. The forthcoming findings from our research expedition will contribute to our understanding of lowlander and indigenous highlander high altitude adaptation.

ABSTRACT

In 2016, the international research team Global Research Expedition on Altitude Related Chronic Health (Global REACH) was established and executed a high altitude research expedition to Nepal. The team consists of ∼45 students, principal investigators and physicians with the common objective of conducting experiments focused on high altitude adaptation in lowlanders and in highlanders with lifelong exposure to high altitude. In 2018, Global REACH travelled to Peru, where we performed a series of experiments in the Andean highlanders. The experimental objectives, organization and characteristics, and key cohort data from Global REACH's latest research expedition are outlined herein. Fifteen major studies are described that aimed to elucidate the physiological differences in high altitude acclimatization between lowlanders (n = 30) and Andean-born highlanders with (n = 22) and without (n = 45) excessive erythrocytosis. After baseline testing in Kelowna, BC, Canada (344 m), Global REACH travelled to Lima, Peru (∼80 m) and then ascended by automobile to Cerro de Pasco, Peru (∼4300 m), where experiments were conducted over 25 days. The core studies focused on elucidating the mechanism(s) governing cerebral and peripheral vascular function, cardiopulmonary regulation, exercise performance and autonomic control. Despite encountering serious logistical challenges, each of the proposed studies was completed at both sea level and high altitude, amounting to ∼780 study sessions and >3000 h of experimental testing. Participant demographics and data relating to acid-base balance and exercise capacity are presented. The collective findings will contribute to our understanding of how lowlanders and Andean highlanders have adapted under high altitude stress.

Relationship between hypertension and geographic altitude: a cross-sectional survey among residents in Tibet

Objective

This study aimed to assess the prevalence of hypertension (HT) among individuals living at different altitudes in Tibet.

Methods

We conducted a stratified cluster survey among 1,631 participants in Tibet living in areas at three different altitudes.

Results

Mean systolic and diastolic blood pressure and body mass index (BMI) values were highest at the lowest altitudes. After adjusting for age and sex, the prevalence of HT at low, medium, and high altitudes was 40.6%, 32.5%, and 20.4%, respectively. The prevalence of HT decreased with increasing altitude and increased with increasing age and BMI value.

Conclusion

Increasing altitude tended to decrease BMI levels, and as a consequence, the prevalence of HT was reduced. National policies and guidelines for HT in Tibet should focus on this relationship.

Low Elevation and Physical Inactivity are Associated with a Higher Prevalence of Metabolic Syndrome in Ecuadorian Adults: A National Cross-Sectional Study

BACKGROUND

Elevation and health-related lifestyles have been associated with the development of metabolic syndrome (MetS). However, such associations have not been investigated extensively in a global context. The present study aimed to determine the associations among elevation of residence, health-related lifestyles, and the risk of MetS in an Ecuadorian adult population.

SUBJECTS AND METHODS

This cross-sectional study was conducted utilizing secondary data from the 2012 Ecuador National Health and Nutrition Survey (ENSANUT-ECU). A total of 6024 adults (1964 men and 4060 women) 20 to 60 years old were included in the study. Elevation was obtained by georeferencing techniques and categorized into low (0-2000 masl) and high (>2001 masl). Dietary intake was measured using a 24-hour recall and health-related lifestyle via risk and physical activity standardized questionnaire. MetS was defined on the basis of the National Cholesterol Education Program Adult Treatment Panel III and the Latin American Diabetes Association criteria. Multiple logistic regression analyses were used to examine whether elevation of residence and health-related lifestyles can increase the risk of MetS.

RESULTS

Residing at low elevation increased prevalence of MetS in men (1.37; 95% CI, 1.05-1.76) and elevated fasting glucose in both men (1.80; 95% CI, 1.32-2.46) and women (1.55; 95% CI, 1.24-1.93) after adjusting for confounders. Additionally, a lack of physical activity was identified as an important factor that raises the risk of increased waist circumference in both men (2.05; 95% CI, 1.22-3.45) and women (1.38; 95% CI, 1.05-1.83) living at low elevation.

CONCLUSION

Our findings suggest that low elevation of residence and physical inactivity are associated with a higher prevalence of MetS in Ecuadorian adults.

Altitude and its inverse association with abdominal obesity in an Andean country: a cross-sectional study

Background: Abdominal obesity represents an accurate predictor of overall morbidity and mortality, which is worrisome because it is also continuously increasing across Andean countries. However, its relationship with altitude remains unclear. The objective of this study was to assess the association between altitude and abdominal obesity in Peru, and how sociodemographic variables impact this association. Methods: We estimated the prevalence of abdominal obesity in Peru and analyzed its association with altitude using the data from the 2012-2013 National Household Survey (ENAHO). During this survey, a representative sample of Peruvians was screened for abdominal obesity, using waist circumference as a proxy, and the Adult Treatment Panel III guidelines cutoffs. Results: Data were analyzed from a sample of 20,489 Peruvians (51% male). The prevalence of abdominal obesity was estimated at 33.6% (95% CI: 32.5 to 34.6%). In Peru, altitude was significantly and inversely associated with abdominal obesity, decreasing with higher altitudes: 1500-2999 meters above mean sea level (MAMSL) vs <1500 MAMSL, adjusted prevalence rate [aPR]= 0.86 (95% CI: 0.75 to 0.97); ≥3000 MAMSL vs <1500 MAMSL, aPR= 0.98 (95% CI: 0.87 to 1.11), when adjusting by age, gender and residence area (rural/urban). However, this association was significantly modified by age and gender ( p< 0.001). Conclusion: Abdominal obesity is highly prevalent in Peru and decreases significantly with altitude, but age and gender modify this association. Thus, abdominal obesity appears to affect older women from low altitudes more than younger men from high altitudes.

Activity of Lipoprotein-Associated Enzymes in Indigenous Children Living at Different Altitudes

BACKGROUND

High altitude is associated with hypobaric hypoxia, and metabolic modifications. In particular, alterations to lipoprotein-associated enzymes have been reported under hypoxia.

OBJECTIVE

To determine the association between paraoxonase 1 (PON-1) and Cholesteryl-ester transfer protein (CETP) activities and altitude in two groups of Argentinean Indigenous schoolchildren living at different altitudes.

METHODS

A cross-sectional study compared 151 schoolchildren from San Antonio de los Cobres (SAC), 3,750 m, with 175 schoolchildren from Chicoana (CH), 1,400 m. Anthropometric data, lipids, apolipoprotein (apo) A-I, apo B, plus PON-1 and CETP activities were determined.

RESULTS

The prevalence of overweight/obesity was significantly lower in SAC than in CH. Z- BMI (0.3 vs 0.7), Apo A-I/Apo B (1.67 vs. 1.85) and PON-1 (170 vs. 243 nmol/mL.min) were significantly lower in SAC than in CH, respectively. Total cholesterol (156 vs 144 mg/dL), triglycerides (TG) (119 vs. 94 mg/dL), apo A-I (133 vs. 128 mg/dL), apo B (84 vs. 73 mg/dL), hematocrit (48 vs. 41%), transferrin (295 vs. 260 mg/dL) and CETP (181 vs. 150%/mL.h) were significantly higher in SAC than in CH. There was a significant univariate association between altitude and transferrin (r0.38), hematocrit (r0.75), TG (r0.24), apo B (r0.29), PON-1 (r-0.40), and CETP (r0.37). Multiple linear regression analyses showed that altitude was significantly associated with children's TG (β = 0.28, R² = 0.14), HDL-C (β = ‒0.27; R² = 0.23), apo B (β = 0.32; R² = 0.14), CETP (β = 0.38; R² = 0.15) and PON-1 (β = ‒0.36; R² = 0.16), adjusted for age, gender and BMI.

CONCLUSION

SAC children presented a more atherogenic lipid profile, plus lower PON1 and higher CETP activities, than CH children.

Eicosapentaenoic Acid Reduces Adiposity, Glucose Intolerance and Increases Oxygen Consumption Independently of Uncoupling Protein 1

SCOPE

Brown adipose tissue (BAT) dissipates energy through uncoupling protein 1 (UCP1) and has been proposed as an anti-obesity target. It was reported previously that a high-fat (HF) diet enriched in eicosapentaenoic acid (EPA) significantly increased UCP1 and other thermogenic markers in BAT. It is hypothesized that these effects are mediated through UCP1-dependent regulation.

METHODS AND RESULTS

Wild-type (WT) and UCP1 knockout (KO) B6 male mice were housed at thermoneutrality and fed a HF diet, without or with eicosapentaenoic acid (EPA)-enriched fish oil. HF-fed KO mice were heavier and had higher BAT lipid content than other groups. Protective effects of EPA in WT, previously observed at 22 °C (reduced adiposity, improved glucose tolerance, and increased UCP1), disappeared at thermoneutrality. Mitochondrial proteins, cytochrome c oxidase subunit 1 (COX I), COX I, II, and IV were reduced in the KO mice compared to WT. Unexpectedly, EPA attenuated weight and fat mass gain and improved glucose tolerance in the KO mice. Finally, EPA increased BAT peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) protein and gene expression, and whole-body oxygen consumption in KO mice, consistent with increased mitochondria DNA (mtDNA)/nuclear DNA (nucDNA) ratio.

CONCLUSIONS

EPA rescued the weight gain and glucose intolerance in UCP1 KO mice at thermoneutrality, independent of UCP1; these effects may be mediated in part via increased oxygen consumption and BAT PGC1α.

Blood pressure levels among Indigenous children living at different altitudes

The objective was to compare blood pressure (BP) levels in 2 groups of Indigenous Argentine school children from similar ethnic backgrounds but living at different altitudes. One hundred and fifty-two (46.3%) children (age, 4-14 years) from San Antonio de los Cobres (SAC), at 3750 m above sea level, and 176 children (53.7%) from Chicoana (CH), at 1400 m above sea level, participated in this cross-sectional study. Data for children's anthropometry, BP, glucose, lipids, vitamin D, and insulin, as well as mothers' height and weight were assessed. Hypertension was defined as BP ≥ 95th percentile. The prevalence of overweight/obesity among children was significantly lower in SAC (n = 17, 11.2%) than in CH (n = 74, 42%) (body mass index (BMI) > 85th percentile per US Centers for Disease Control and Prevention norms). However, the prevalence of hypertension was significantly higher among children in SAC (n = 15, 9.9%) than among those in CH (n = 2, 1.1%). Children were divided into 4 groups by mean arterial BP quartiles for comparison by ANOVA. As mean arterial BP increased, age, BMI, glucose, triglycerides, triglycerides/high-density lipoprotein cholesterol, and insulin levels increased significantly. Multiple linear regression analyses showed that children's mean arterial BP was significantly associated with altitude adjusted for confounding variables (R² = 0.42). Furthermore, when mean arterial BP was replaced by systolic BP (R² = 0.51) or diastolic BP (R² = 0.33), similar results were obtained. Our results suggest that Indigenous children who live permanently at high altitude have higher levels of BP, adjusted for confounding variables. Routine BP measurements conducted in the SAC community could be essential for the prevention of cardiovascular disease.

Type 2 diabetes markers in indigenous Argentinean children living at different altitudes

BACKGROUND

Exposure to hypoxia at high altitude is increasingly being recognized as a risk factor for metabolic diseases.

OBJECTIVE

To determine the association between Type 2 diabetes (T2D) risk factors and altitude in two groups of Argentinean indigenous schoolchildren who live permanently at different altitudes.

METHODS

This cross-sectional study compared 142 schoolchildren from San Antonio de los Cobres (SAC), 3750 m above sea level, with 171 from Chicoana (CH), 1400 m. Data for children's anthropometry, blood pressure and lipids, as well as mothers' height and weight were assessed.

RESULTS

There was not a significant difference in age between SAC (9.0 + 2y) and CH (9.4 + 2y) children. However, mean children's weight (29 vs. 38 kg), height (130 vs. 138 cm), BMI (17 vs. 19 kg/m2), and HDL-C (46 vs. 48 mg/dL) were significantly lower in SAC than in CH, respectively. In contrast, systolic blood pressure (87 vs. 70 mmHg), cholesterol (157 vs. 148 mg/dL), and triglycerides (104 vs. 88 mg/dL) were significantly higher in SAC than in CH, respectively. There was not a significant difference in age (33.2 + 7y vs. 34.4 + 8y) and BMI (26.2 + 4y vs. 28 + 5y) between SAC and CH mothers. Multiple linear regression analyses showed that children's blood pressure (R2 = 0.38), triglycerides (R2 = 0.21), and HDL-C (R2 = 0.16) were significantly associated with altitude, adjusted for confounding variables.

CONCLUSION

This study shows that indigenous Argentinean children living at 3750 meters have higher T2D risk compared with those living at 1400 meters above sea level.

Inverse Association Between Metabolic Syndrome and Altitude: A Cross-Sectional Study in an Adult Population of Ecuador

Background: Metabolic syndrome (MetS) is characterized by the clustering of hyperglycemia, hypertension, hypertriglyceridemia, low high-density lipoprotein cholesterol levels and central adiposity. Altitude has been proposed as a protective factor to prevent the development of MetS and its components. Aim: To determine whether living at geographical elevation is associated with MetS and its individual components after adjustment for potential confounders in an Ecuadoran population. Methods: The study included 260 Ecuadoran university graduates over 20 years of age, from the coastal or the Andean Altiplano region. The altitude of residence was imputed with the postal code of each participant residence according to the data of the Ecuadoran Geophysical Institute of the National Polytechnic School. MetS was defined according to the harmonizing definition. Logistic regression models were fitted to assess the relationship between altitude level and the prevalence of MetS and its individual components. To test the internal validity, re-sampling techniques were used (1,000 bootstrap samples). Results: Living at high altitude was associated with less hypercholesterolemia (OR = 0.24; p < 0.001), hyperglycemia (OR = 0.25; p < 0.05) and MetS (OR = 0.24; p < 0.05), after adjusting for potential confounders. At high altitude the bootstrapped logistic regression models showed lower prevalence of hypercholesterolemia (OR = 0.30; p < 0.05), hyperglycemia (OR = 0.22; p < 0.001) and MetS (OR = 0.28; p < 0.05). The MetS score (0-5 points) showed a reduction in the number of MetS components at high altitude compared to sea level (B = -0.34; p = 0.002). A statistically significant lower self-reported energy intake was found in high altitude compared to sea level after adjustment for potential confounders (p < 0.001). Conclusion: In the present study concerning a small Ecuadoran population composed of highly educated adults living at the coast and the Andean Altiplano, living at high altitude (2,758-2,787 m) was associated with a lower prevalence of MetS, hypercholesterolemia and hyperglycemia, compared to the participants at sea level (4-6 m). In addition, an inverse association between altitude and self-reported energy intake was found after adjusting for covariates, suggesting a physiological role of appetite at high altitude even in acclimated subjects.

miRNA array analysis of plasma miRNA alterations in rats exposed to a high altitude hypoxic environment

In the present study, the microRNA (miRNA) expression profiles of rats exposed to high altitude hypoxia and normal conditions were obtained from miRNA array analysis. Bioinformatics analyses, including the use of the Gene Oncology and Kyoto Encyclopedia of Genes and Genomes databases, were used to identify the genes and pathways, which were specifically associated with high altitude hypoxic environment‑associated miRNAs. A total of 26 miRNAs were differentially expressed in the two groups, comprising six upregulated and 20 downregulated miRNAs. In the present study, a novel pattern of upregulated miRNAs and their associated pathways were constructed, including proteoglycans in cancer, spliceosome, gluamatergic synapse, glycolysis/gluconeogenesis, Foxo, cGMP‑PKG and p53 signaling pathways, which may provide novel targets for diagnosing and understanding the mechanism of high altitude hypoxia‑induced disease.

The Effects of High Altitude on Glucose Homeostasis, Metabolic Control, and Other Diabetes-Related Parameters: From Animal Studies to Real Life

Exposure to high altitude activates several complex and adaptive mechanisms aiming to protect human homeostasis from extreme environmental conditions, such as hypoxia and low temperatures. Short-term exposure is followed by transient hyperglycemia, mainly triggered by the activation of the sympathetic system, whereas long-term exposure results in lower plasma glucose concentrations, mediated by improved insulin sensitivity and augmented peripheral glucose disposal. An inverse relationship between altitude, diabetes, and obesity has been well documented. This is the result of genetic and physiological adaptations principally to hypoxia that favorably affect glucose metabolism; however, the contribution of financial, dietary, and other life-style parameters may also be important. According to existing evidence, people with diabetes are capable of undertaking demanding physical challenges even at extreme altitudes. Still, a number of issues should be taken into account, including the increased physical activity leading to changes in insulin demands and resistance, the performance of measurement systems under extreme weather conditions and the potential deterioration of metabolic control during climbing expeditions. The aim of this review is to present available evidence in the field in a comprehensive way, beginning from the physiology of glucose homeostasis adaptation mechanisms to high altitudes and ending to what real life experience has taught us.

Current health status and its risk factors of the Tsarang villagers living at high altitude in the Mustang district of Nepal

Background

Epidemiology of noncommunicable diseases (NCDs) such as obesity and diabetes mellitus (DM) are influenced by multiple hosts and environmental factors. This study aims to investigate the prevalence of NCDs and determine their risk factors among the adults residing in an isolated village situated at a rural highland of Nepal.

Methods

A cross-sectional survey was conducted in a village located at 3570 m. Each 188 randomly selected participants of age ≥ 18 years old answered a questionnaire and took a full physical exam that included biomedical measurements of glycosylated hemoglobin (HbA1c).

Results

The prevalence of intermediate hyperglycemia and DM was 31.6% and 4.6% respectively, and the prevalence of hypoxemia (SpO₂ < 90%) was 27.1%. A multiple logistic regression analysis for factors for the prevalence of glucose intolerance (HbA1c ≥ 6%) revealed older age (odds ratio [OR] 1.11, 95% confidence interval [CI] 1.06–1.16, for every 1 year increase) and SpO₂ (OR for hypoxemia 3.58, 95% CI 1.20–10.68, vs SpO₂ ≥ 90%).

Conclusions

Tibetan highlanders in the remote mountainous Mustang valley of Nepal have high prevalence of impaired glucose metabolism which could be related to hypoxemia imposed by the hypoxic conditions of high altitude living.

On the origin of obesity: identifying the biological, environmental and cultural drivers of genetic risk among human populations

Genetic predisposition to obesity presents a paradox: how do genetic variants with a detrimental impact on human health persist through evolutionary time? Numerous hypotheses, such as the thrifty genotype hypothesis, attempt to explain this phenomenon yet fail to provide a justification for the modern obesity epidemic. In this critical review, we appraise existing theories explaining the evolutionary origins of obesity and explore novel biological and sociocultural agents of evolutionary change to help explain the modern-day distribution of obesity-predisposing variants. Genetic drift, acting as a form of 'blind justice,' may randomly affect allele frequencies across generations while gene pleiotropy and adaptations to diverse environments may explain the rise and subsequent selection of obesity risk alleles. As an adaptive response, epigenetic regulation of gene expression may impact the manifestation of genetic predisposition to obesity. Finally, exposure to malnutrition and disease epidemics in the wake of oppressive social systems, culturally mediated notions of attractiveness and desirability, and diverse mating systems may play a role in shaping the human genome. As an important first step towards the identification of important drivers of obesity gene evolution, this review may inform empirical research focused on testing evolutionary theories by way of population genetics and mathematical modelling.

Activity of the antioxidant enzyme paraoxonase in Argentinean children living at high altitude

Background: Children living at high altitude in San Antonio de los Cobres (SAC), Argentina, were shown to have lower high-density lipoprotein cholesterol (HDL-C) levels than Buenos Aires (BA) children. HDL antioxidant capacity is mainly attributed to paraoxonase1 (PON1).

Objective: To compare PON1 activity in indigenous SAC vs. BA children.

Methods: A cross-sectional study compared 158 SAC vs. 97 BA children (6–16 years). Anthropometric data and lipoprotein profile were measured. PON1 was evaluated employing paraoxon (PON) and phenylacetate (ARE) activity.

Results: The prevalence of overweight/obesity was lower in SAC than in BA children (18.3 vs. 30.9%). Triglycerides (1.34 vs. 0.90 mmol/l), apo B (0.84 vs.0.72 g/l), apo A-I (1.33 vs. 1.27 g/l), and ARE activity (100 vs. 90 µmol/ml/min) were higher, while HDL-C (1.16 vs. 1.32 mmol/l) and PON activity (170 vs. 203 nmol/ml/min) were lower in SAC than in BA. Separate multiple linear regression analyses showed that SAC children had significantly higher triglyceride (Beta −0.38), apo B (Beta −0.34), and ARE (Beta −0.36) plus lower HDL-C (Beta 0.33) and PON (Beta 0.25) compared with BA; adjusted for age, gender, and BMI.

Conclusion: SAC showed an unfavorable lipoprotein profile, lower PON and higher ARE activities compared with BA children, suggesting the presence of altered HDL metabolism and antioxidant capacity.

The prevalence of obesity and metabolic syndrome in Tibetan immigrants living in high altitude areas in Ladakh, India

OBJECTIVE

To examine the prevalence of obesity and related cardiovascular disease risk factors among Tibetan immigrants living in high altitude areas.

RESEARCH METHODS & PROCEDURES

A total of 149 Tibetan immigrants aged 20 years and over were recruited in 2016 in Ladakh, India. Anthropometric indices and biochemical factors were measured. Using the provided Asia-Pacific criteria from the World Health Organization, overweight and obese status were determined. Metabolic syndrome (MetS) was defined according to the American Heart Association.

RESULTS

In general, men were older, taller, and had a greater amount of fasting glucose, and uric acid when compared to women. The prevalence of overweight, general obesity, and central obesity was 23.4, 42.6, and 42.6% in men and 7.8, 64.7, and 69.6% in women, respectively. The prevalence of MetS was 10.6% in men and 33.3% in women, respectively. In older subjects, the prevalence of obesity and MetS was found to be greater. In both genders, the prevalence of hypertension, central obesity, and MetS was significantly different among these body mass index (BMI) groups. Compared to the non-central obesity group, the central obesity group has higher weight, BMI, body fat, hip circumference, systolic and diastolic BP, and prevalence of hypertension. No relationship was found between the prevalence of diabetes and fasting glucose and BMI groups or central obesity groups in both genders.

CONCLUSIONS

Among this group of Tibetan immigrants living in high altitude areas, women have a higher prevalence of obesity and MetS than men. No relationship was found between diabetes and obesity.

Long-Term Health Outcomes in High-Altitude Pulmonary Hypertension

Robinson, Jeffrey C., Cheryl Abbott, Christina A. Meadows, Robert C. Roach, Benjamin Honigman, and Todd M. Bull. Long-term health outcomes in high-altitude pulmonary hypertension. High Alt Med Biol. 18:61-66, 2017.

BACKGROUND

High-altitude pulmonary hypertension (HAPH) is one of several known comorbidities that effect populations living at high altitude, but there have been no studies looking at long-term health consequences of HAPH. We aimed to determine whether HAPH during adolescence predisposes to significant pulmonary hypertension (PH) later in life, as well as identify how altitude exposure and HAPH correlate with functional class and medical comorbidities.

METHODS

We utilized a previously published cohort of 28 adolescents from Leadville, Colorado, that underwent right heart catheterization at 10,150 ft (3094 m) in 1962, with many demonstrating PH as defined by resting mean pulmonary arterial pressure ≥25 mmHg. We located participants of the original study and had living subjects complete demographic and health surveys to assess for the presence of PH and other medical comorbidities, along with current functional status.

RESULTS

Seventy-five percent of the individuals who participated in the original study were located. Those with HAPH in the past were more prone to have exertional limitation corresponding to WHO functional class >1. Fifty-five years following the original study, we found no significant differences in prevalence of medical comorbidities, including PH, among those with and without HAPH in their youth.

CONCLUSIONS

Surveyed individuals did not report significant PH, but those with HAPH in their youth were more likely to report functional limitation. With a significant worldwide population living at moderate and high altitudes, further study of long-term health consequences is warranted.

Obesity as a Conditioning Factor for High-Altitude Diseases

Obesity, a worldwide epidemic, has become a major health burden because it is usually accompanied by an increased risk for insulin resistance, diabetes, hypertension, cardiovascular diseases, and even some kinds of cancer. It also results in associated increases in healthcare expenditures and labor and economic consequences. There are also other fields of medicine and biology where obesity or being overweight play a major role, such as high-altitude illnesses (acute mountain sickness, hypoxic pulmonary hypertension, and chronic mountain sickness), where an increasing relationship among these two morbid statuses has been demonstrated. This association could be rooted in the interactions between obesity-related metabolic alterations and critical ventilation impairments due to obesity, which would aggravate hypobaric hypoxia at high altitudes, leading to hypoxemia, which is a trigger for developing high-altitude diseases. This review examines the current literature to support the idea that obesity or overweight could be major conditioning factors at high altitude.

Living at Higher Altitude and Incidence of Overweight/Obesity: Prospective Analysis of the SUN Cohort

BACKGROUND

Residence at high altitude has been associated with lower obesity rates probably due to hypoxia conditions. However, there is no evidence of this association in a free-living population.

OBJECTIVES

We assessed the association between the altitude where each participant of a Spanish cohort (the SUN Project) was living and the incidence of overweight/obesity.

METHODS

The SUN Project is a dynamic, prospective, multipurpose cohort of Spanish university graduates with a retention rate of 89%. We included in the analysis 9 365 participants free of overweight/obesity at baseline. At the baseline questionnaire, participants reported their postal code and the time they had been living in their city/village. We imputed the altitude of each postal code according to the data of the Spanish National Cartographic Institute and categorized participants in tertiles. We used Cox regression models to adjust for potential confounding variables.

RESULTS

During a median follow-up of 10 years, we identified 2 156 incident cases of overweight/obesity. After adjusting for sex, age, time of residence at current city, baseline body mass index, physical activity, sedentarism and years of education (≤ 3 years, ≥ 4 years, Master/PhD), those participants in the third tertile (>456 m) exhibited a statistically significant 14% reduction in the risk of developing overweight/obesity in comparison to those in the first tertile (<124 m) (adjusted HR = 0.86; 95% CI: 0.77, 0.96).

CONCLUSIONS

Living in cities of higher altitude was inversely associated with the risk of developing overweight/obesity in a cohort of Spanish university graduates.

Synergistic Inhibitory Effects of Hypoxia and Iron Deficiency on Hepatic Glucose Response in Mouse Liver

Hypoxia and iron both regulate metabolism through multiple mechanisms, including hypoxia-inducible transcription factors. The hypoxic effects on glucose disposal and glycolysis are well established, but less is known about the effects of hypoxia and iron deficiency on hepatic gluconeogenesis. We therefore assessed their effects on hepatic glucose production in mice. Weanling C57BL/6 male mice were fed an iron-deficient (4 ppm) or iron-adequate (35 ppm) diet for 14 weeks and were continued in normoxia or exposed to hypoxia (8% O2) for the last 4 weeks of that period. Hypoxic mice became hypoglycemic and displayed impaired hepatic glucose production after a pyruvate challenge, an effect accentuated by an iron-deficient diet. Stabilization of hypoxia-inducible factors under hypoxia resulted in most glucose being converted into lactate and not oxidized. Hepatic pyruvate concentrations were lower in hypoxic mice. The decreased hepatic pyruvate levels were not caused by increased utilization but rather were contributed to by decreased metabolism from gluconeogenic amino acids. Pyruvate carboxylase, which catalyzes the first step of gluconeogenesis, was also downregulated by hypoxia with iron deficiency. Hypoxia, and more so hypoxia with iron deficiency, results in hypoglycemia due to decreased levels of hepatic pyruvate and decreased pyruvate utilization for gluconeogenesis. These data highlight the role of iron levels as an important determinant of glucose metabolism in hypoxia.

Increased Cardiometabolic Risk and Worsening Hypoxemia at High Altitude

Miele, Catherine H., Alan R. Schwartz, Robert H. Gilman, Luu Pham, Robert A. Wise, Victor G. Davila-Roman, Jonathan C. Jun, Vsevolod Y. Polotsky, J. Jaime Miranda, Fabiola Leon-Velarde, and William Checkley. Increased cardiometabolic risk and worsening hypoxemia at high altitude. High Alt Med Biol. 17:93-100, 2016.-Metabolic syndrome, insulin resistance, diabetes, and dyslipidemia are associated with an increased risk of cardiovascular disease. While excessive erythrocytosis is associated with cardiovascular complications, it is unclear how worsening hypoxemia of any degree affects cardiometabolic risk factors in high-altitude populations. We studied the relationship between daytime resting oxyhemoglobin saturation and cardiometabolic risk factors in adult participants living in Puno, Peru (3825 m above sea level). We used multivariable logistic regression models to study the relationship between having a lower oxyhemoglobin saturation and markers of cardiometabolic risk. Nine hundred and fifty-four participants (mean age 55 years, 52% male) had information available on pulse oximetry and markers of cardiometabolic risk. Average oxyhemoglobin saturation was 90% (interquartile range 88%-92%) and 43 (4.5%) had excessive erythrocytosis. Older age, decreased height-adjusted lung function, and higher body mass index (BMI) were associated with having an oxyhemoglobin saturation ≤85%. When adjusting for age, sex, socioeconomic status, having excessive erythrocytosis, and site, we found that each 5% decrease in oxyhemoglobin saturation was associated with a higher adjusted odds of metabolic syndrome (OR = 1.35, 95% CI: 1.07-1.72, p < 0.04), insulin resistance as defined by homeostasis model assessment-insulin resistance (HOMA-IR) >2 mass units (OR = 1.29, 95% CI: 1.00-1.67, p < 0.05), hemoglobin A1c ≥6.5% (OR = 1.66, 95% CI: 1.09-2.51, p < 0.04), and high sensitivity C-reactive protein (hs-CRP) ≥3 mg/L (OR = 1.46, 95% CI: 1.09-1.96, p < 0.01). In high-altitude populations in Puno, Peru, a higher BMI and lower pulmonary function were associated with lower resting daytime oxyhemoglobin saturation. Lower resting oxyhemoglobin saturation, in turn, was associated with higher odds of having multiple unfavorable cardiometabolic factors. Worsening hypoxia of any degree in high-altitude dwellers may be an independent risk factor for cardiovascular disease.

Inverse association between altitude and obesity: A prevalence study among andean and low-altitude adult individuals of Peru

OBJECTIVE

To determine the association between altitude and obesity in a nationally representative sample of the Peruvian adult population.

METHODS

This is a cross-sectional analysis of publicly available data from the Food and Nutrition National Center (CENAN, Peru), period 2009-2010. The Prevalence ratio of obesity and abdominal obesity was determined as a measure of association. Obesity and abdominal obesity were diagnosed based on direct anthropometric measurements.

RESULTS

The final data set consisted of 31,549 individuals ≥20 years old. The prevalence ratio of obesity was as follows: 1.00 between 0 and 499 m (reference category), 1.00 (95% confidence interval 0.87-1.16) between 500-1,499 m, 0.74 (0.63-0.86) between 1,500-2,999 m, and 0.54 (0.45-0.64) at ≥3,000 m, adjusting for age, sex, self-reported physical activity, out-migration rate, urbanization, poverty, education, and geographical latitude and longitude. In the same order, the adjusted prevalence ratio of abdominal obesity was 1.00, 1.01 (0.94-1.07), 0.93 (0.87-0.99), and 0.89 (0.82-0.95), respectively. We found an interaction between altitude and sex and between altitude and age (P < 0.001, for both interactions) on the association with obesity and abdominal obesity.

CONCLUSIONS

Among Peruvian adult individuals, we found an inverse association between altitude and obesity, adjusting for multiple covariates. This adjusted association varied by sex and age.

Comparison Between HDL-C Levels in Argentine Indigenous Children Living at High Altitudes and U.S. Children

BACKGROUND

Studies have shown low levels of high-density lipoprotein cholesterol (HDL-C) in indigenous children versus urban children from Argentina. We hypothesized that indigenous children living at high altitudes might have lower HDL-C levels compared with U.S. children, probably due to ambient hypoxia, lifestyle conditions, or ethnicity. This study was designed (1) to compare HDL-C levels in Argentinean indigenous children with those reported in the 2011-2012 National Health and Nutrition Examination Survey (NHANES) for U.S. children and (2) to determine the association between HDL-C and adiposity in both groups.

SUBJECTS AND METHODS

A cross-sectional study of 1,232 (631 females) Argentinean indigenous schoolchildren (4-14 years old) from San Antonio de los Cobres (SAC) was performed between November 2011 and November 2014. Anthropometric measures were performed in the whole group and compared with those of 2,151 U.S. children (1,034 females). However, HDL-C concentrations were measured in 905 SAC children and compared with those of 1,451 U.S. children. Analyses were done incorporating sampling weights for age in both samples to obtain unbiased estimates. In the case of NHANES the weights provided by each individual in the 2011-2012 NHANES demographic file were used, whereas in the SAC sample the weights were obtained using the census data provided by the 2010 National Statistics and Censuses Institute of Argentina.

RESULTS

The prevalence of overweight/obesity was significantly lower in SAC (135/1,232; 11%) than in the United States (759/2,151; 35%). However, the prevalence of low levels of HDL-C was significantly higher in SAC (298/905; 33%) than in the United States (142/1,451; 10%). The prevalence of low levels of HDL-C increased significantly in both groups as body mass index categories increased. Multiple logistic regression analysis showed that SAC children had nine and a half times the odds of having low levels of HDL-C compared with U.S. children, adjusted for confounding variables (odds ratio = 9.55; 95% confidence interval, 7.18-12.71).

CONCLUSIONS

This study shows a high prevalence of low levels of HDL-C in indigenous Argentinean children 4-14 years of age living at high altitudes compared with U.S. children.

Cardiometabolic risk factors in native populations living at high altitudes

BACKGROUND

It is generally accepted that metabolic changes that take place in individuals exposed to high elevation are because of ambient hypoxia, which occurs as a consequence of a low total atmospheric pressure. The discovery of hypoxia inducible factor 1 (HIF1), a transcription factor, has been a breakthrough in the understanding of adaption to high altitudes.

OBJECTIVE

The purpose of the present review was to discuss specific epidemiological aspects of cardiovascular disease (CVD) risk factors and their mechanisms in vulnerable, understudied populations living at high altitudes.

RESULTS

Obesity prevalence has been inversely associated with elevation. HIF1 has been related to plasma leptin--a hormone secreted by adipose tissue that produces negative feedback on appetite--and inversely associated with obesity. Diverse factors, such as genetics, chronic hypoxia, diet and lifestyle behaviours, could have an influence on the high dyslipidaemia rates of high-altitude natives. Hypoxia could mediate the effects of altitude on human physiology, including lipid metabolism. Genetic studies suggest that dyslipidaemia could be related to the HIF1. Hypoxia inhibits oxidative phosphorylation and stimulates the oxygen signalling pathway through the HIF1. Low fasting glycaemia in individuals at high altitudes has been shown. An increased GLUT4 protein content in skeletal muscle in response to hypoxia has been reported and could be associated with lower glucose levels. Given the high prevalence of dyslipidaemia and the low prevalence of obesity and diabetes in these impoverished high-altitude communities, changes in lifestyle including decreased physical activity and the consumption of a more westernised diet would likely increase the prevalence of CVD related mortality.

CONCLUSIONS

Control over major CVD risk factors, when identified early, could be the key to reducing morbidity and mortality in patients with limited access to medical services such as Native populations.

Waist Circumference Percentiles in Indigenous Argentinean School Children Living at High Altitudes

BACKGROUND

Central obesity is associated with increased risk of type 2 diabetes.

OBJECTIVES

The study objectives were to develop waist circumference (WC) percentiles, to determine if WC is associated with metabolic risk, and to compare our WC percentiles with those reported in the 2007-2010 National Health and Nutrition Examination Survey (NHANES).

METHODS

A cross-sectional study of 1232 children (606 boys ) 5-14 years was performed from 2011 to 2014 in indigenous Koya children from northwestern Argentina. Anthropometric characteristics, glucose, lipids, and insulin levels were measured. Sex-specific reference percentiles were computed using the Lambda-Mu-Sigma (LMS) method. We obtained 2007-2010 NHANES data for comparison with our results.

RESULTS

Compared with the NHANES 90th percentile, WC values for children in this study were lower by an average of 11.05 cm for girls and 12.66 cm for boys. The prevalence of low high-density lipoprotein cholesterol (HDL-C) was 11.8% in children with WC ≤50th percentile, 10.3% in children with WC >50th-70th percentile, 17.5% in children with WC >70th-90th percentile, and 21.3% in children with WC >90th percentile. The prevalence of high triglycerides (TG) was 19.5% in children with WC ≤50th percentile, 19.9% in children with WC >50th-70th percentile, 28.8% in children with WC >70th-90th percentile, and 39.7% in children with WC >90th percentile. Multiple logistic regression analyses showed that high TG values (>150 mg/dL) were significantly associated with WC [odds ratio (OR)] 1.05; 95% confidence interval (CI) 1.03-1.08; and low HDL-C values (<35 mg/dL) were significantly associated with WC (OR 1.04; 95% CI 1.01-1.06), adjusted for age and gender.

CONCLUSION

We present for the first time WC reference data for indigenous Koya children ages 5-14 years. There was a significant association between WC and dyslipidemia in this community. Compared with the NHANES WC percentiles, our WC values were lower. These differences possibly reflect ethnicity or the lower prevalence of obesity.

Ambient Temperature and Prevalence of Obesity: A Nationwide Population-Based Study in Korea

Background

Recent studies have suggested a possible association between outdoor or indoor temperature and obesity. We aimed to examine whether ambient temperature is associated with the prevalence of obesity or abdominal obesity in the Korean population.

Methods

Data on anthropometric, socio-demographic, laboratory and lifestyle factors were retrieved from National Health Insurance System data obtained in 2009–2010. Thirty years (1981 to 2010) of meteorological parameters for 71 observation areas were acquired from the Korea Meteorological Administration. Included in this analysis were 124,354 individuals. A body mass index (BMI) ≥ 25 kg/m² and a waist circumference (WC) ≥ 90 cm (men) or 85 cm (women) were considered to represent obesity and abdominal obesity, respectively.

Results

The mean annual temperature (MAT) ranged from 6.6°C to 16.6°C, and BMI was positively correlated with MAT (r = 0.0078, P = 0.0065). WC was positively correlated with MAT (r = 0.0165, P < 0.0001) and negatively correlated with the number of days with mean temperature < 0°C (DMT0; r = –0.0129, P = 0.0002). After adjusting for age, sex, smoking status, alcohol consumption, exercise, income, residential area and altitude, the odds ratios (95% CI) for obesity and abdominal obesity in the highest quintile MAT group were 1.045 (1.010, 1.081) and 1.082 (1.042, 1.124), respectively, compared with the lower four quintiles of the MAT group. Similarly, subjects in the area of the lowest quintile of DMT0 had significantly higher odds of abdominal obesity compared with the higher four quintile groups of DMT0.

Conclusion

This study finds an association between ambient temperature and prevalence of obesity in the Korean population when controlling for several confounding factors. Adaptive thermogenesis might be a possible explanation for this phenomenon.

Metabolic aspects of high-altitude adaptation in Tibetans

NEW FINDINGS

What is the topic of this review? The topic of this review is how Tibetans have adapted genetically to high altitude, particularly with reference to altitude-induced changes in metabolism. What advances does it highlight? It highlights recent work on metabolic phenotyping in Tibetans and demonstrates that selected genetic haplotypes influence their metabolism of fats and glucose. Recent studies have identified genes involved in high-altitude adaptation in Tibetans. Three of these genes (EPAS1, EGLN1 and PPARA) are associated with decreased haemoglobin levels compared with non-Tibetans living at altitude. Consistent with the phenotype, EGLN1 in Tibetans has a gain-of-function mutation that confers a higher affinity for oxygen, hence less sensitivity to hypoxia. Considering the demands imposed upon metabolism in meeting energy demands despite limitations on fuel oxidation, we hypothesized that other selected genes might alter metabolism to allow adaptation to altitude despite the desensitization of the upstream hypoxia sensing caused by the EGLN1 mutation that results in the failure to sense hypoxia. A shift in fuel preference to glucose oxidation and glycolysis at the expense of fatty acid oxidation would provide adaptation to decreased oxygen availability. Measurements of serum metabolites from Tibetans living at high altitude are consistent with this hypothesis; the EPAS1 haplotype is significantly associated with increased lactate levels (suggesting increased anaerobic metabolism), and the PPARA haplotype and serum free fatty acids are positively related (suggesting decreased fat oxidation). These data suggest that the high-altitude adaptations may offer protection from diabetes at high altitude but increase the risk of diabetes at lower elevations and/or with adoption of a non-traditional diet. It should also be considered in future work in the field that because iron is a cofactor for EGLN1, there may be significant associations of phenotypes with the significant degrees of variation seen in tissue iron among human populations.

Glucose homeostasis during short-term and prolonged exposure to high altitudes

Most of the literature related to high altitude medicine is devoted to the short-term effects of high-altitude exposure on human physiology. However, long-term effects of living at high altitudes may be more important in relation to human disease because more than 400 million people worldwide reside above 1500 m. Interestingly, individuals living at higher altitudes have a lower fasting glycemia and better glucose tolerance compared with those who live near sea level. There is also emerging evidence of the lower prevalence of both obesity and diabetes at higher altitudes. The mechanisms underlying improved glucose control at higher altitudes remain unclear. In this review, we present the most current evidence about glucose homeostasis in residents living above 1500 m and discuss possible mechanisms that could explain the lower fasting glycemia and lower prevalence of obesity and diabetes in this population. Understanding the mechanisms that regulate and maintain the lower fasting glycemia in individuals who live at higher altitudes could lead to new therapeutics for impaired glucose homeostasis.

Hypoxic Conditioning as a New Therapeutic Modality

Preconditioning refers to a procedure by which a single noxious stimulus below the threshold of damage is applied to the tissue in order to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic preconditioning relies on complex and active defenses that organisms have developed to counter the adverse consequences of oxygen deprivation. The protection it confers against ischemic attack for instance as well as the underlying biological mechanisms have been extensively investigated in animal models. Based on these data, hypoxic conditioning (consisting in recurrent exposure to hypoxia) has been suggested a potential non-pharmacological therapeutic intervention to enhance some physiological functions in individuals in whom acute or chronic pathological events are anticipated or existing. In addition to healthy subjects, some benefits have been reported in patients with cardiovascular and pulmonary diseases as well as in overweight and obese individuals. Hypoxic conditioning consisting in sessions of intermittent exposure to moderate hypoxia repeated over several weeks may induce hematological, vascular, metabolic, and neurological effects. This review addresses the existing evidence regarding the use of hypoxic conditioning as a potential therapeutic modality, and emphasizes on many remaining issues to clarify and future researches to be performed in the field.

Effect of iron supplementation on the expression of hypoxia-inducible factor and antioxidant status in rats exposed to high-altitude hypoxia environment

Iron and oxygen are essential substance for cellular activity in body tissues. Hypoxia-inducible factors (HIFs) can respond to available oxygen changes in the cellular environment and regulate the transcription of a series of target genes. The study was conducted to investigate the effects of iron supplementation on the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and antioxidant status in rats exposed to high-altitude hypoxia environment. Forty rats were divided into control (CON), hypobaric hypoxia (HH), and hypobaric hypoxia plus ferrous sulfate (FeSO4) (9.93 mg/kg body weight (BW)/day) (HFS) and hypobaric hypoxia plus iron glycinate chelate (Fe-Gly) (11.76 mg/kg BW/day) (HFG) groups. Results showed that Fe-Gly effectively alleviated weight loss and intestinal mucosa damage induced by hypobaric hypoxia, whereas FeSO4 aggravated hypobaric hypoxia-induced weight loss, liver enlargement, spleen atrophy, and intestinal damage. Iron supplementation decreased liver superoxide dismutase (T-SOD) and catalase (CAT) activity (P < 0.01) and increased iron concentration in the liver compared to HH group (P < 0.001). Moreover, Fe-Gly upregulated liver transferrin expression in messenger RNA (mRNA) level (P < 0.05) and downregulated serum erythropoietin (EPO) concentration (P < 0.01) and liver HIF-1α expression level (P < 0.05 in mRNA level; P < 0.001 in protein level) compared to HH group. The study indicated that FeSO4 supplementation at high altitudes aggravated the oxidative damage of tissues and organs that could be mediated through production of malondialdehyde (MDA) and inhibition antioxidant enzyme activities. Fe-Gly can protect hypobaric hypoxia-induced tissues injury. Moreover, iron supplementation at high altitudes affected HIF-1α-mediated regulating expression of targeting genes such as EPO and transferrin. The study highlights that iron supplementation under hypobaric hypoxia environment has possible limitation, and efficient supplementation form and dosage need careful consideration.

Ambient temperature and prevalence of obesity in the Spanish population: The Di@bet.es study

OBJECTIVE

The aim of this study was to examine possible associations between ambient temperature and obesity in the Spanish population using an ecological focus.

METHODS

The Di@bet.es study is a national, cross-sectional, population-based survey of cardiometabolic risk factors and their association with lifestyle.

SAMPLE

5,061 subjects in 100 clusters.

VARIABLES

Clinical, demographic and lifestyle survey, physical examination, and blood sampling. The mean annual temperature (°C) for each study site was collected from the Spanish National Meteorology Agency (1971-2000).

RESULTS

The prevalence rates of obesity in the different geographical areas divided according to mean annual temperature quartiles were 26.9% in quartile 1 (10.4-14.5°C), 30.5% in quartile 2 (14.5-15.5°C), 32% in quartile 3 (15.5-17.8°C), and 33.6% in quartile 4 (17.8-21.3°C) (P = 0.003). Logistic regression analyses including multiple socio-demographic (age, gender, educational level, marital status) and lifestyle (physical activity, Mediterranean diet score, smoking) variables showed that, as compared with quartile 1, the odd ratios for obesity were 1.20 (1.01-1.42), 1.35 (1.12-1.61), and 1.38 (1.14-1.67) in quartiles 2, 3, and 4, respectively (P = 0.001 for difference, P < 0.001 for trend).

CONCLUSIONS

Our study reports an association between ambient temperature and obesity in the Spanish population controlled for known confounders.

Inverse association between diabetes and altitude: a cross-sectional study in the adult population of the United States

OBJECTIVE

To determine whether geographical elevation is inversely associated with diabetes, while adjusting for multiple risk factors.

METHODS

This is a cross-sectional analysis of publicly available online data from the Behavioral Risk Factor Surveillance System, 2009. Final dataset included 285,196 US adult subjects. Odds ratios were obtained from multilevel mixed-effects logistic regression analysis.

RESULTS

Among US adults (≥20 years old), the odds ratio for diabetes was 1.00 between 0 and 499 m of altitude (reference), 0.95 (95% confidence interval, 0.90-1.01) between 500 and 1,499 m, and 0.88 (0.81-0.96) between 1,500 and 3,500 m, adjusting for age, sex, body mass index, ethnicity, self-reported fruit and vegetable consumption, self-reported physical activity, current smoking status, level of education, income, health status, employment status, and county-level information on migration rate, urbanization, and latitude. The inverse association between altitude and diabetes in the US was found among men [0.84 (0.76-0.94)], but not women [1.09 (0.97-1.22)].

CONCLUSIONS

Among US adults, living at high altitude (1,500-3,500 m) is associated with lower odds of having diabetes than living between 0 and 499 m, while adjusting for multiple risk factors. Our findings suggest that geographical elevation may be an important factor linked to diabetes.

Lower obesity rate during residence at high altitude among a military population with frequent migration: a quasi experimental model for investigating spatial causation

We sought to evaluate whether residence at high altitude is associated with the development of obesity among those at increased risk of becoming obese. Obesity, a leading global health priority, is often refractory to care. A potentially novel intervention is hypoxia, which has demonstrated positive long-term metabolic effects in rats. Whether or not high altitude residence confers benefit in humans, however, remains unknown. Using a quasi-experimental, retrospective study design, we observed all outpatient medical encounters for overweight active component enlisted service members in the U.S. Army or Air Force from January 2006 to December 2012 who were stationed in the United States. We compared high altitude (>1.96 kilometers above sea level) duty assignment with low altitude (<0.98 kilometers). The outcome of interest was obesity related ICD-9 codes (278.00-01, V85.3x-V85.54) by Cox regression. We found service members had a lower hazard ratio (HR) of incident obesity diagnosis if stationed at high altitude as compared to low altitude (HR 0.59, 95% confidence interval [CI] 0.54–0.65; p<0.001). Using geographic distribution of obesity prevalence among civilians throughout the U.S. as a covariate (as measured by the Centers for Disease Control and Prevention and the REGARDS study) also predicted obesity onset among service members. In conclusion, high altitude residence predicts lower rates of new obesity diagnoses among overweight service members in the U.S. Army and Air Force. Future studies should assign exposure using randomization, clarify the mechanism(s) of this relationship, and assess the net balance of harms and benefits of high altitude on obesity prevention.