Body fat distribution and their associations with cardiovascular risk, insulin resistance and β-cell function: are there differences between men and women?

Objective: The objective was to examine the independent and gender-specific effects of WC and BMI on CVD risk factors, insulin resistance and β-cell function.

Design: A cross-sectional study of 2931 adults aged 20-79 years was carried out in Fujian province by multi-stratified sampling from July 2007 to May 2008. Gender-specific differences of WC and BMI on CVD risk factors, insulin resistance and β-cell function were displayed jointly by WC and BMI tertiles. The homeostasis model assessment of insulin resistance (HOMA-IR) index and the quantitative insulin-sensitivity check index (QUICKI): l/(log G0 ± log I0) were used to estimate insulin sensitivity; insulin secretion was assessed using the HOMA-β index; β-cell function was quantified as the ratio of the incremental insulin to glucose responses over the first 30 min during the OGTT (△I30/△G30). The oral disposition index (DIo) was calculated as ΔI(30) /ΔG(30) × 1/fasting insulin. The Matsuda index is defined as 10,000/sqrt (FBG × FPI × [G × I]) where FPG is fasting glucose, FPI is fasting insulin, G is mean glucose during the OGTT (calculated from glucose samples at 0, 30, and 120 min), and I is mean insulin during the OGTT (calculated from insulin samples at 0, 30, and 120 min).

Results: Waist circumference and BMI correlated with each other in both men (0.756, p < 0.001) and women (0.728, p < 0.001). The two indexes were independently associated with CVD risk factors (such as hypertension, metabolic syndrome, and dyslipidaemia) in both men and women. BMI was better than WC in assessing the risk of diabetes in men (p = 0.003 for BMI, and p = 0.234 for WC), while WC was better than BMI in predicting diabetes in women (p < 0.001 for WC, and p = 0.831 for BMI). There were significant associations between BMI and insulin resistance or β-cell function even after adjustment for WC except for DIo in male subjects, but WC only associated with HOMA-IR positively or the Matsuda index and QUICKI negatively after adjustment for BMI. For women, associations between WC and insulin resistance or β-cell function remained strong even after adjustment for BMI besides DIo. However, there were no independent relations of BMI to insulin resistance and β-cell function except for Matsuda index with a significant negative association after adjustment for WC in women.

Conclusion: Body mass index and WC were independently associated with CVD risk factors. There were differences in the gender-specific relevance of measures of body fat distribution in assessing the insulin resistance, β-cell function and thus the risk of diabetes. Therefore, WC should be measured in addition to BMI to assess CVD risk accurately and implement efficient treatment strategies.