Adjustment for Waist Circumference Reveals a U-Shaped Association Between Glycated Hemoglobin Levels and Body Mass Index in Young Adults

OBJECTIVES

Body mass index (BMI) is used to assess adiposity worldwide. However, additional adjustment for waist circumference (WC), a surrogate marker of abdominal fat, may be capable of revealing a latent relationship between low body weight and glycated hemoglobin (A1C) concentration. Here, we investigated the relationship between A1C and BMI in young adults, adjusting for WC.

METHODS

We reviewed A1C, BMI, WC and other clinical data in a cross-sectional study of 26,475 apparently healthy Japanese people 20 to 39 years of age who were undergoing health check-ups.

RESULTS

Although the values of most serum parameters were high in subjects with a high BMI in both younger (20 to 29 years of age, n=10,810) and older subjects (30 to 39 years of age, n=15,665), A1C had a J-shaped relationship with BMI category in younger subjects, regardless of sex. A traditional linear model via a generalized linear model showed that in younger subjects, an inverse association of A1C level with BMI category (19 to 26.9 kg/m² vs. ≤18.9 kg/m²) was identified after adjustment for WC. This indicates positive associations between A1C and BMI categories of ≤18.9 (beta=0.06; p<0.0001), 19.0 to 20.9 (beta=0.03; p<0.01) and ≥27.0 kg/m² (beta=0.08; p<0.0001), in contrast to individuals with BMIs of 23.0 to 24.9 kg/m². Similarly, in older subjects, BMIs ≤18.9 kg/m² were associated with A1C levels but to a lesser extent (beta=0.04; p<0.05) than in younger subjects.

CONCLUSIONS

Additional adjustment of BMI for WC revealed a latent U-shaped association between A1C concentration and BMI, particularly in young adults; this deserves further investigation.

Kanagawa Investigation of the Total Check-up Data from the National database (KITCHEN): protocol for data-driven population-based repeated cross-sectional and 6-year cohort studies

INTRODUCTION

The unmitigated incidence of cardiometabolic diseases, such as type 2 diabetes and metabolic syndrome, has gained attention in Japan. 'Big data' can be useful to clarify conflicting observations obtained from studies with small samples and about rare conditions that are often neglected. We epidemiologically address these issues using data from health check-ups conducted in Kanagawa Prefecture, the prefecture with the second largest population in Japan, in the Kanagawa Investigation of the Total Check-up Data from the National Database (KITCHEN).

METHODS AND ANALYSIS

This research consists of a series of population-based cross-sectional studies repeated from 2008-2014 and 6-year cohort studies. Since 2017, we have reviewed the data of people living in Kanagawa Prefecture who underwent a health check-up mainly for general health and the prevention of metabolic syndrome. The sample size ranges from 1.2 million to 1.8 million people in the cross-sectional studies and from 370 000 to 590 000 people in the cohort studies. These are people aged 40-74 years, whose clinical parameters were measured and who responded individually to a questionnaire. We investigate potential associations and causalities of various aetiologies, including diabetes and metabolic syndrome, using clinical data and lifestyle information. With multidisciplinary analysis, including data-driven analysis, we expect to obtain a wide range of novel findings, to confirm indeterminate previous findings, especially in terms of cardiometabolic disease, and to provide new perspectives for human health promotion and disease prevention.

ETHICS AND DISSEMINATION

Ethical approval was received from the Ethics Committee of Kanagawa University of Human Services (10-43). The protocol was approved in December 2016 by the Japanese Ministry of Health, Labour and Welfare (No. 121). The study results will be disseminated through open platforms including journal articles, relevant conferences and seminar presentations.

Potential common factors associated with predisposition to common cold in middle-aged and elderly Japanese: A community-based cross-sectional study

People worldwide frequently catch a common cold, which occasionally develops into secondary severe conditions such as pneumonia. However, it is unclear whether predisposition to the common cold is associated with the individual's characteristics including age, body weight, lifestyles, diets, and intestinal functions, besides exposure to a responsible pathogen. We addressed this issue epidemiologically considering many relevant clinical factors.We reviewed data from a cross-sectional study consisting of 39,524 apparently healthy Japanese aged 40 to 79 years (26,975 men and 12,549 women) who underwent a checkup in 2007. Self-reported predisposition to common cold (SPCC) and relevant clinical conditions and parameters were considered.We observed no significant difference in most clinical parameters including age, body mass index (BMI), glycated hemoglobin (HbA1c), and prevalence of men and current smokers between subjects with and without SPCC. In univariate analysis, circulating white blood cell (WBC) count and serum alanine-aminotransferase (ALT) were significantly higher in subjects with SPCC than in those without, whereas serum high-density lipoprotein cholesterol (HDL-C) and duration of sleep were lower. In logistic regression analysis after full adjustment for relevant confounding factors, BMI categories except BMI of ≥27.0 kg/m were significantly associated with SPCC compared with BMI of 23.0 to 24.9 kg/m. Short duration of sleep (≤5 hours), occasional alcohol drinking, and no-exercise were significantly associated with SPCC compared with 7 hours sleep duration, no-drinking alcohol, and low frequent exercise (twice per month), respectively. All gastrointestinal disorders (gastric complaints, constipation, and diarrhea) were independently associated with SPCC. Imbalanced diet and taking a snack were also associated with SPCC in a degree dependent manner. Furthermore, WBC count, serum ALT, and HDL-C (as continuous variables) were associated with SPCC (HDL-C was inversely), whereas no significant association was observed between SPCC and age, smoking, HbA1c, and pharmacotherapy for diabetes, hypertension, and dyslipidemia.Our results demonstrated that multifactorial conditions and parameters might be simultaneously associated with the predisposition to common cold. Prospective studies including detailed common cold questionnaire and measurements are needed to confirm currently suspected causative and protective factors.

Unexpected association between subclinical hearing loss and restorative sleep in a middle-aged and elderly Japanese population

OBJECTIVE

Hearing loss may be associated with certain sleep abnormalities. We recently reported that subclinical hearing loss (SHL) was more prevalent in individuals in a broad Japanese population who slept longer than 8 h; however, the underlying mechanism was unknown. Therefore, we investigated the association between SHL and self-reported restorative sleep (RS), assessed by questionnaire, in a database of 33,888 Japanese aged 40-69 years without overt or diagnosed hearing loss (20,225 men, 13,663 women).

RESULTS

The proportion of individuals with RS (more than half of the subjects) was significantly higher in the group with bilateral than with unilateral SHL at 4000 Hz and intact hearing; however, that was not the case at 1000 Hz, independent of age (P < 0.0001, two-way analysis of variance). Multivariate logistic regression analysis showed that bilateral SHL at 4000 Hz, but not at 1000 Hz, was significantly associated with RS. This relationship was independent of potential relevant confounders, including age, sex, and cardiometabolic risk factors. The present study extends our earlier work by revealing an unexpected association between early hearing impairment and satisfactory sleep in a middle-aged and elderly population. This association requires further confirmation regarding the possible underlying mechanism and clinical relevance.

Age-dependent changes in the association between sleep duration and impaired glucose metabolism

AIM

To investigate whether the association between sleep duration and impaired glucose metabolism varies among younger and older populations.

METHODS

We reviewed data of self-reported habitual sleep duration per night, HbA1c levels, and clinically relevant factors in a cross-sectional checkup database of 75472 Japanese from the general population aged 20-79 years (51695 men and 23777 women). Associations of prediabetes (HbA1c ≥ 5.7% and/or diabetic pharmacotherapy) or diabetes (HbA1c ≥ 6.5% and/or diabetic pharmacotherapy) with short and long sleep durations compared with a reference sleep duration (7 h) were investigated by multivariate logistic regression analysis. We controlled for potential relevant confounders, including age, sex, and work duration per day according to younger and older subjects.

RESULTS

As age advanced, sleep duration became longer and this increase in the 40s and 50s was two times greater in men than in women. This finding was accompanied by a deterioration in HbA1c levels. In subjects aged younger than 40 years (n = 32929), HbA1c levels were inversely and linearly correlated with sleep duration in both sexes. However, in subjects aged 40 years or older (n = 42543), HbA1c levels showed a non-linear relationship against sleep duration with a nadir at 7 h. Multivariate logistic regression analysis showed that in younger subjects, short durations of sleep (≤ 5 h and 6 h) were positively associated with prediabetes (both P < 0.001), but a long duration of sleep (≥ 8 h) was inversely associated with prediabetes (P < 0.001). These associations remained significant after adjustment for relevant confounders, including age, sex, and work duration per day (ORs = 1.20, 95%CI: 1.05-1.37, P < 0.001; ORs = 1.12, 95%CI: 1.02-1.24, P < 0.05; and ORs = 0.84, 95%CI: 0.72-0.99, P < 0.05, respectively). In contrast, in older subjects, besides an association of prediabetes with a short duration of sleep (≤ 5 h) (ORs = 1.12, 95%CI: 1.03-1.21, P < 0.01), diabetes was significantly associated with a long duration of sleep (≥ 8 h) (ORs = 1.11, 95%CI: 1.02-1.25, P < 0.05).

CONCLUSION

A short sleep duration may be associated with prediabetes throughout life. However, the association between a long sleep duration and glucose metabolism can change with aging.

Prevalent hyperglycemia in older obese population and age-dependent convergence of obese indices: Results of a cross-sectional study of Japanese generations over the adult life span

PURPOSE/AIM

An age-dependent decline has been observed in the association between obesity and type 2 diabetes, a major comorbidity of obesity, although the evidence is limited. Therefore, we investigated the association and the plausible underlying mechanism in a large epidemiological study.

MATERIALS AND METHODS

We examined the association between the degree of obesity and hyperglycemia in five age groups (20-39, 40-49, 50-59, 60-69, and 70-85 years) in a cross-sectional study of 78,776 apparently healthy Japanese men and women who underwent a checkup in 2012. Hyperglycemia was defined as glycosylated hemoglobin (HbA1c) of ≥5.7% and/or pharmacotherapy for diabetes.

RESULTS

The incidence of hyperglycemia was three times higher in the 70-85-year-old group (62%) than in the 20-39-year-old group (20%) in obese individuals (body mass index [BMI] ≥ 27.0 kg/m(2)). However, the incidence was 12 times higher in reference-weight individuals (21.0-22.9 kg/m(2); 48% and 4%, respectively). As age increased, mean BMI and waist circumference approached certain non-obese ranges (22-24 kg/m(2) and 80-86 cm, respectively), even in hyperglycemic subjects. Logistic regression analysis revealed an age-dependent decline in the association between obesity and hyperglycemia, relative to that in reference-weight individuals.

CONCLUSIONS

Our results confirmed the previously reported age-dependent decline in the association between obesity and hyperglycemia, although hyperglycemia was still prevalent in older obese subjects than in older reference-weight subjects. Therefore, the decline in the association may be accelerated due to an age-dependent increase in the prevalence of hyperglycemia in reference-weight individuals.

Effects of Weight Loss Speed on Kidney Function Differ Depending on Body Mass Index in Nondiabetic Healthy People: A Prospective Cohort

Background

Obesity is associated with diabetes mellitus and cardiovascular diseases. However, it has been reported that weight loss is associated with incident chronic kidney disease (CKD) in healthy males. The purpose of this prospective cohort study is to investigate the effects of weight loss on kidney function in healthy people in terms of body mass index (BMI) and gender.

Methods

A total of 8447 nondiabetic healthy people were enrolled in the Saitama Cardiometabolic Disease and Organ Impairment Study, Japan. Relationships between estimated glomerular filtration rate (eGFR) change, BMI, and BMI change were evaluated using 3D-scatter plots with spline and generalized additive models (GAMs) adjusted for baseline characteristics.

Results

The subjects were stratified into four groups according to BMI. The mean±standard deviations for males and females were, respectively, 40.11±9.49, and 40.3±9.71 years for age and 76.39±17.72 and 71.49±18.4 ml/min/1.73m² for eGFR. GAMs showed that a decreasing BMI change (<-1 kg/m²/year) was associated with a decreasing eGFR change in males with high normal BMIs (22 kg/m²≤BMI<25 kg/m²). A decreasing BMI change (<-2 kg/m²/year) was associated with an increasing eGFR change in overweight males (25 kg/m²≤BMI). Among underweight females (BMI<18.5 kg/m²), decreasing BMI was observed with decreasing eGFR.

Conclusions

These findings suggest that the benefit and risk of weight loss in relation to kidney function differs depending on BMI and weight loss speed, especially in males.

Alcohol and Exercise Affect Declining Kidney Function in Healthy Males Regardless of Obesity: A Prospective Cohort Study

Background

Although lifestyle is associated with metabolic syndrome and cardiovascular diseases, there has been no sufficient evidence of lifestyles on incident chronic kidney disease (CKD). The purpose of this prospective cohort study is to investigate the effects of lifestyles on kidney function in healthy people.

Methods

A total of 7473 healthy people were enrolled in this Saitama Cardiometabolic Disease and Organ Impairment Study, Japan. Data on alcohol consumption, exercise frequency, and sleep duration were collected. The outcome event was incident CKD or decrease in estimated glomerular filtration rate (eGFR) by >25% in 3 years.

Results

Subjects were classified into four groups according to body mass index and gender. Mean ± standard deviation of age was 38.8±10.5 years; eGFR, 78.1±15.2 ml/min/1.73m². In the male groups, multivariate logistic regression models showed that the outcome events were associated with a small amount of alcohol consumed (20 to 140g of alcohol/week) (ref. more than 140g of alcohol/week); non-obese male, adjusted odds ratio 1.366 (95% confidence interval, 1.086, 1.718); obese male (body mass index ≥25), 1.634 (1.160, 2.302); and with frequent exercise (twice a week or more) (ref. no exercise); non-obese male, 1.417 (1.144, 1.754); obese male, 1.842 (1.317, 2.577). Sleep duration was not associated with the outcome events.

Conclusion

These findings suggest that, regardless of obesity, a small amount of alcohol consumed and high exercise frequency were associated with the increased risk of loss of kidney function in the male groups.

Association of hyperglycemia in a general Japanese population with late-night-dinner eating alone, but not breakfast skipping alone

The unhealthy habit of late-night-dinner eating (LNDE) is often observed in adults. Since LNDE can lead to breakfast skipping (BS) the next morning, we examined the associations of LNDE and BS with hyperglycemia (HbA1c ≥ 5.7% and/or pharmacotherapy for diabetes), separately and in combination, in 61,364 apparently healthy Japanese adults aged 30–70 years. Although LNDE alone was significantly associated with hyperglycemia, even after adjustment for body mass index, BS alone was not. Our results indicate that hyperglycemia in the general Japanese population is associated with LNDE alone, but not BS alone.

Uric acid level has a U-shaped association with loss of kidney function in healthy people: a prospective cohort study

Background

The relationship between hyperuricemia and chronic kidney disease (CKD) has been found in various observational studies. Although hypouricemia is associated with cardiovascular events, it has not been established as a risk factor for CKD. We investigated the relationship between serum uric acid level and the loss of kidney function and incident CKD in healthy people.

Materials and Methods

Healthy people were enrolled in this community-based prospective cohort study, the Saitama Cardiometabolic Disease and Organ Impairment Study, Japan. The analysis was conducted on 4188 subjects followed up for at least 3 years, 3102 for 6 years and 1052 for 9 years. Their data including glomerular filtration rate (eGFR) decline were examined every three years. The outcome event was incident CKD or the decrease in eGFR by more than 25% in three years. Multivariate statistical models were adjusted for the baseline characteristics.

Results

The following data was obtained: mean±SD age, male, 39.6±10.4 years, female 38.4±10.8 years; eGFR, male, 81.9±16.4 ml/min/1.73m2, female, 82.1±17.5 ml/min/1.73m2; serum uric acid level, male, 5.8±1.2 mg/dl, female, 4.1±0.9 mg/dl. Both low and high serum uric acid levels were associated with the outcome and eGFR decline in males (multivariate logistic additional additive models, linear p = 0.0001, spline p = 0.043; generalized additive models, linear p = 0.0001, spline p = 0.012). In subjects with low serum uric acid levels (male, <5 mg/dl; female, <3.6 mg/dl), multivariate linear mixed models showed that low serum uric acid levels were associated with eGFR decline in a time-dependent manner (male, p = 0.0001; female, p = 0.045).

Conclusion

This study showed that low as well as high levels of uric acid are associated with the loss of kidney function. Hypouricemia is a candidate predictor of kidney function decline in healthy people.

Excess body weight affects HbA1c progression irrespective of baseline HbA1c levels in Japanese individuals: a longitudinal retrospective study

PURPOSE/AIM

Obese individuals with normal HbA1c levels and low-body-weight individuals with high-normal HbA1c levels are frequently encountered in clinical settings, but the effects of these phenotypes on the onset of diabetes are poorly understood. Therefore, we addressed this issue in a longitudinal study.

MATERIALS AND METHODS

We analyzed clinical parameters, including body mass index (BMI) and HbA1c levels, in 5325 non-diabetic Japanese people aged 20-75 years who underwent four medical checkups between 1999 (baseline) and 2007. The subjects were then classified into six baseline BMI categories, each of which was divided into two HbA1c groups, resulting in a total of 12 groups.

RESULTS

In 405 obese subjects with a normal baseline HbA1c (BMI ≥ 27.0 kg/m(2), HbA1c 5.2-5.6%), the mean HbA1c level increased during the study period, and 50.9% developed prediabetes/diabetes. In contrast, in 77 low-body-weight subjects with a high-normal baseline HbA1c (BMI ≤ 18.9 kg/m(2), HbA1c 5.7-6.4%), the mean HbA1c level remained constant. Similar changes occurred in the other groups during the study, resulting in a linear increase in HbA1c levels with increasing BMI.

CONCLUSION

Our results suggest that approximately half of the obese individuals with HbA1c in the normal range develop prediabetes or diabetes within 8 years, whereas low-body-weight individuals with high-normal HbA1c are less likely to exhibit worsening in glycemia. Thus, excess body weight may be the primary therapeutic target to prevent the early onset of diabetes, regardless of the individual's HbA1c.

Subclinical hearing loss, longer sleep duration, and cardiometabolic risk factors in Japanese general population

Hearing loss leads to impaired social functioning and quality of life. Hearing loss is also associated with sleeping disorders and cardiometabolic risk factors. Here, we determined whether subclinical hearing loss is associated with sleep duration and cardiometabolic risk factors in a cross-sectional and longitudinal study of healthy Japanese general population. 48,091 men and women aged 20–79 years who underwent medical checkups were included in a cross-sectional study, and 6,674 were included in an 8-year longitudinal study. The prevalence of audiometrically determined hearing loss (>25 dB) at 4000 and 1000 Hz increased significantly with increasing sleep duration in any age strata. Logistic regression analysis showed that compared with reference sleep duration (6 h) longer sleep duration (≥8 h) was significantly associated with hearing loss, even after adjusting for potential confounding factors. Simultaneously, hearing loss was significantly associated with male sex, diabetes, and no habitual exercise. In the longitudinal study, the risk of longer sleep duration (≥8 h) after 8 years was significantly greater in subjects with hearing loss at 4000 Hz at baseline. In conclusion, current results suggest a potential association of subclinical hearing loss with longer sleep duration and cardiometabolic risk factors in a Japanese general population.