Risk factors for insulin resistance in midlife Singaporean women

Objectives: To understand the extent to which risk factors for insulin resistance are mediated by body mass index (BMI), visceral adipose tissue (VAT), physical activity and performance, and the inflammatory markers interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and high-sensitivity C-reactive protein (hs-CRP). Study design: A wide range of socio-demographic characteristics of Chinese, Malay and Indian women attending routine gynecologic care in Singapore were prospectively collected. Physical performance was objectively measured by hand grip strength and the Short Physical Performance Battery. Percent VAT was determined by dual-energy X-ray absorptiometry. Fasting serum concentrations of glucose, insulin, IL-6, TNF-alpha, and hs-CRP were measured. Main outcome measure: was insulin resistance, expressed as the homeostatic model assessment of insulin resistance (HOMA-IR). Results: 1159 women were analyzed, mean age 56.3 (range 45-69) years, comprising women of Chinese (84.0%), Indian (10.2%), and Malay (5.7%) ethnic origins. The adjusted mean differences for obesity (0.66, 95% CI 0.32-1.00), VAT area in the highest vs lowest tertile (1.03, 95% CI 0.73-1.34), low physical performance (0.63, 95% CI 0.05-1.24), and highest vs lowest tertile of TNF-alpha (0.35, 95% CI 0.13-0.57) were independently associated with HOMA-IR. Women of Malay and Indian ethnicity had higher crude HOMA-IR than Chinese women. However, after adjustment for obesity, VAT, physical performance, and TNF-alpha, no differences in mean HOMA-IR remained, when comparing Chinese women with those of Malay ethnicity (0.27, 95% CI -0.12 to 0.66) and with those of Indian ethnicity (0.30, 95% CI -0.01 to 0.66). Conclusions: Insulin resistance was independently associated with obesity, high VAT, low physical performance, and high levels of TNF-alpha in midlife Singaporean women. These variables entirely explained the significant differences in insulin resistance between women of Chinese, Malay and Indian ethnicity.