Serum 25-hydroxyvitamin D, diabetes, and ethnicity in the third national health and nutrition examination survey

OBJECTIVE— To determine the association between serum 25-hydroxyvitamin D (25OHD) and diabetes risk and whether it varies by ethnicity.
RESEARCH DESIGN AND METHODS— We performed an analysis of data from participants who attended the morning examination of the Third National Health and Nutrition Examination Survey (1988–1994), a cross-sectional survey of a nationally representative sample of the U.S. population. Serum levels of 25OHD, which reflect vitamin D status, were available from 6,228 people (2,766 non-Hispanic whites, 1,736 non-Hispanic blacks, and 1,726 Mexican Americans) aged ≥20 years with fasting and/or 2-h plasma glucose and serum insulin measurements.
RESULTS— Adjusting for sex, age, BMI, leisure activity, and quarter of year, ethnicityspecific odds ratios (ORs) for diabetes (fasting glucose ≥7.0 mmol/l) varied inversely across quartiles of 25OHD in a dose-dependent pattern (OR 0.25 [95% CI 0.11– 0.60] for non-Hispanic whites and 0.17 [0.08–0.37] for Mexican Americans) in the highest vitamin D quartile (25OHD ≥81.0 nmol/l) compared with the lowest 25OHD (≥43.9 nmol/l). This inverse association
was not observed in non-Hispanic blacks. Homeostasis model assessment of insulin resistance (loge) was inversely associated with serum 25OHD in Mexican Americans (P ≥ 0.0024) and non-Hispanic whites (P≥0.058) but not non-Hispanic blacks (P≥0.93), adjusting for confounders.
CONCLUSIONS— These results show an inverse association between vitamin D status and diabetes, possibly involving insulin resistance, in non-Hispanic whites and Mexican Americans. The lack of an inverse association in non-Hispanic blacks may reflect decreased sensitivity to vitamin D and/or related hormones such as the parathyroid hormone.

Waist circumference, waist-hip ratio and BMI and their correlation with cardiovascular risk factors in Australian adults

Objectives. To compare body mass index (BMI), waist circumference and waist–hip ratio (WHR) as indices of obesity and assess the respective associations with type 2 diabetes, hypertension and dyslipidaemia.

Design and setting. A national sample of 11 247 Australians aged ≥25 years was examined in 2000 in a cross-sectional survey.

Main outcome measures. The examination included a fasting blood sample, standard 2-h 75-g oral glucose tolerance test, blood pressure measurements and questionnaires to assess treatment for dyslipidaemia and hypertension. BMI, waist circumference and WHR were measured to assess overweight and obesity.

Results. The prevalence of obesity amongst Australian adults defined by BMI, waist circumference and WHR was 20.8, 30.5 and 15.8% respectively. The unadjusted odds ratio for the fourth vs. first quartile of each obesity measurement showed that WHR had the strongest relationship with type 2 diabetes, dyslipidaemia (women only) and hypertension. Following adjustment for age, however, there was little difference between the three measures of obesity, with the possible exceptions of hypertension in women, where BMI had a stronger association, and dyslipidaemia in women and type 2 diabetes in men, where WHR was marginally superior.

Conclusions. Waist circumference, BMI and WHR identified different proportions of the population, as measured by both prevalence of obesity and cardiovascular disease (CVD) risk factors. Whilst WHR had the strongest correlations with CVD risk factors before adjustment for age, the three obesity measures performed similarly after adjustment for age. Given the difficulty of using age-adjusted associations in the clinical setting, these results suggest that given appropriate cut-off points, WHR is the most useful measure of obesity to use to identify individuals with CVD risk factors.