Signatures of high altitude adaptation in Tibeto-Burman tribes of the Darjeeling Hill Region

OBJECTIVES

The long-term isolation, endogamy practices, and environmental adaptations have shaped the enormous human diversity in India. The genetic and morphological variations in mainland Indians are well studied. However, the data on the Indian Himalayan populations are scattered. Thus, the present study attempts to understand variations in the selected parameter among four Tibeto-Burman speaking ethnic tribal populations from the Darjeeling Hill Region (DHR) in the Eastern Himalaya Biodiversity Hotspot region of India.

METHODS

A total of 178 healthy male individuals (Lepcha 98, Sherpa 31, Bhutia 27, and Tibetans 22) living at an altitudinal range of 1467-2258 m above the sea level were studied for the 10 parameters namely, weight (kg), height (cm), body mass index (BMI) (kg/m² ) systolic and diastolic pressure (mm of Hg), pulse rate (per minute), saturation of peripheral oxygen (SPO₂ ) (%), hemoglobin (g/dl), hematocrit (HCT) (%), and blood glucose (mg/dl). The data was statistically analyzed using analysis of variance and multiple linear regression methods.

RESULTS

Our analysis revealed comparatively lower hemoglobin and HCT levels, and higher systolic and diastolic blood pressure in the Sherpas followed by the Tibetans. This may be reflecting the persistence of high-altitude adaptation signatures even in lowlands. Interestingly, the Tibetans differed significantly from other populations in terms of their higher body weight, height, and BMI.

CONCLUSION

Thus, our study showed the persistence of high altitude signatures in Tibetans and Sherpa inhabited the DHR. Additionally, we also observed significant differences in the anthropometric and physiological parameters among the Tibeto-Burman populations of the DHR.

Association between Altitude and the Framingham Risk Score: A Cross-Sectional Study in the Peruvian Adult Population

To determine the association between altitude and the Framingham risk score in the Peruvian population, we performed a cross-sectional analytical study of data collected by the 2017–2018 Food and Nutrition Surveillance by Life Stages survey. The outcome of this study was the Framingham 10-year cardiovascular disease event risk prediction, which is composed of six modifiable and non-modifiable coronary risk factors. A generalized linear model (GLM) of the gamma family and log link function was used to report the crude and adjusted β coefficients. Several sensitivity analyses were performed to assess the association of interest. Data from a total of 833 surveyed participants were included. After adjusting for educational level, poverty level, alcohol consumption, physical activity level, the presence of any limitation, obesity, and area of residence, it was observed that altitude ≥ 2500 m above sea level (β = −0.42 [95% CI: −0.69 to −0.16]) was negatively and significantly associated with a decrease in the Framingham 10-year risk score. High altitude was significantly and negatively associated with Framingham 10-year risk scores. Our results will allow prevention strategies considering modifiable risk factors to avoid the development of cardiovascular diseases, especially in people living at low altitudes.

Blood Pressure Variation with Altitudes in Children: A Cross-Sectional Observational Study from Himalayan Hills

OBJECTIVES

We aimed to evaluate blood pressure (BP) in Indian children who had similar demographic characteristics but hailed from different altitudes.

METHODS

BP of school going children, aged 5 to 12 years, at five different locations varying in altitude (near sea level: n = 425; 2000 feet: n = 244; 4000 feet: n = 248; 6000 feet: n = 242 and 8000 feet: n = 250) was measured in a mountainous district in Himalaya. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded by aneroid sphygmomanometer in the sitting posture using a calibrated instrument and four trained resident doctors. The average of three readings was taken.

RESULTS

Of the 1229 children whose data were analyzed, 50.4% were boys. SBP showed a progressive rise from 99.5 (4.00) mmHg [mean (standard deviation)] at near sea level to 106.7 (4.17) mmHg at 8000 feet. Similarly, DBP showed a rise from 60.1 (3.67) mmHg to 66.8 (4.58) mmHg over the same altitude range. Analysis of covariance for BP variation with altitude, with age as covariate, indicated a modest but statistically significant rise in both SBP and DBP with altitude. Higher BP values was noted among children residing at higher than at lower altitude (0.8% at sea level to 18.8% at 8000 feet). Correlations between SBP and DBP values and height and weight, though positive and significant at p < 0.01 level, were weak.

CONCLUSIONS

These data will help in correct interpretation of BP readings in children residing at high altitude.

Residential elevation and its effects on hypertension incidence among older adults living at low altitudes: a prospective cohort study

Background

Research on the relationship between residential altitude and hypertension incidence has been inconclusive. Evidence at low altitudes (i.e., <1,500 m) is scarce, let alone in older adults, a population segment with the highest hypertension prevalence. Thus, the objective of this study is to determine whether hypertension risk may be affected by altitude in older adults living at low altitudes.

Methods

This prospective cohort study collected data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). We selected 6,548 older adults (≥65 years) without hypertension at baseline (2008) and assessed events by the follow-up surveys done in 2011, 2014, and 2018 waves. The mean altitude of 613 residential units (county or district) in which the participants resided was extracted from the Digital Elevation Model (DEM) of the National Aeronautics and Space Administration (NASA) and was accurate to within 30 m. The Cox regression model with penalized splines examined the linear or nonlinear link between altitude and hypertension. A random-effects Cox regression model was used to explore the linear association between altitude and hypertension.

Results

The overall rate of incident hypertension was 8.6 per 100-person years. The median altitude was 130.0 m (interquartile range [IQR] = 315.5 m). We observed that the exposure–response association between altitude and hypertension incidence was not linear. The shape of the exposure–response curve showed that three change points existed. Hypertension risk increased from the lowest to the first change point (247.1 m) and slightly fluctuated until the last change point (633.9 m). The risk decreased above the last change point. According to the categories stratified by the change points, altitude was only significantly associated with hypertension risk (hazard ratio [HR] = 1.003; 95% confidence interval [CI] = 1.002–1.005) under the first change point (247.1 m) after adjusting for related covariates.

Conclusion

Our study found that the association between altitude and hypertension risk might not be linear. We hope the further study can be conducted to confirm the generality of our findings.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1265/ehpm.22-00001.

Impact of urbanisation and altitude on the incidence of, and risk factors for, hypertension

BACKGROUND

Most of the data regarding the burden of hypertension in low-income and middle-income countries comes from cross-sectional surveys instead of longitudinal studies. We estimated the incidence of, and risk factors for, hypertension in four study sites with different degree of urbanisation and altitude.

METHODS

Data from the CRONICAS Cohort Study, conducted in urban, semiurban and rural areas in Peru, was used. An age-stratified and sex-stratified random sample of participants was taken from the most updated census available in each site. Hypertension was defined as systolic blood pressure ≥140 mm Hg, or diastolic blood pressure ≥90 mm Hg, or self-report physician diagnosis and current treatment. The exposures were study site and altitude as well as modifiable risk factors. Incidence, incidence rate ratios (IRRs), 95% CIs and population-attributable fractions (PAFs) were estimated using generalised linear models.

RESULTS

Information from 3237 participants, mean age 55.8 (SD±12.7) years, 48.4% males, was analysed. Overall baseline prevalence of hypertension was 19.7% (95% CI 18.4% to 21.1%). A total of 375 new cases of hypertension were recorded, including 5266 person-years of follow-up, with an incidence of 7.12 (95% CI 6.44 to 7.88) per 100 person-years. Individuals from semiurban site were at higher risk of hypertension compared with highly urbanised areas (IRR=1.76; 95% CI 1.39 to 2.23); however, those from high-altitude sites had a reduced risk (IRR=0.74; 95% CI 0.58 to 0.95). Obesity was the leading risk factor for hypertension with a great variation according to study site with PAF ranging from 12.5% to 42.4%.

CONCLUSIONS

Our results suggest heterogeneity in the progression towards hypertension depending on urbanisation and site altitude.