OBJECTIVE: Diabetes in Asia constitutes approximately half of the global burden. Although insulin resistance and incidence of type 2 diabetes differ substantially between ethnic groups within Asia, the reasons for these differences are poorly understood.We evaluated to what extent body fatness, adiponectin levels and inflammation mediate the relationship between ethnicity and insulin resistance in an Asian setting. DESIGN: Cross-sectional population-based study. SUBJECTS: In total, 4136 adult Chinese, Malays and Asian Indians residing in Singapore. MEASUREMENTS: Insulin resistance was assessed using homeostasis model assessment (HOMA-IR) and systemic inflammation by C-reactive protein (CRP). Data were analyzed using path analysis. RESULTS: HOMA-IR was highest in Asian Indians, intermediate in Malays and lowest in Chinese (Po0.001). The difference in HOMA-IR between Malays and Chinese disappeared after adjusting for body mass index (BMI). For the comparison of Asian Indians with Chinese, the association between ethnicity and HOMA-IR was mediated by BMI (men: 32.9%; women: 48.5%), BMI-adjusted waist circumference (men: 6.1%; women: 3.5%), and CRP (men: 5.1%; women: 5.6%), and unidentified factors (men: 47.2%; women: 26.5%). Part of the mediating effects of body fatness was indirect through effects of body fatness on CRP and adiponectin concentrations. CONCLUSION: Mediators of ethnic differences in insulin resistance differed markedly depending on the ethnic groups compared. General adiposity explained the difference in insulin resistance between Chinese and Malays, whereas abdominal fat distribution, inflammation and unexplained factors contributed to excess insulin resistance in Asian Indians as compared with Chinese and Malays. These findings suggest that interventions targeting excess weight gain can reduce ethnic disparities in insulin resistance among Asian Indians, Chinese and Malays.

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The effects of a chronic (21-day) skin infusion of a variant of insulin-like growth factor I (IGF-I) (long-Arg3-IGF-I; LR3IGF-I) on short-term (48 h) responses of skin metabolism and 21-day plasma hormone concentration, wool-follicle characteristics and wool production were investigated in well-fed castrated Romney sheep. A bilateral arteriovenous preparation was used to infuse LR3IGF-I continuously into the skin on one abdominal flank and saline into the other abdominal flank of six sheep; a further six sheep had one flank infused with saline (controls). LR3IGF-I caused an initial (4-24 h) reduction in the plasma concentrations of amino acids, especially tyrosine, valine and lysine, and, after 24 h, significant (P < 0.05) reductions in blood oxygen and plasma glucose concentrations. After 4 h of LR3IGF-I infusion, there was a significant increase in blood flow (P < 0.05) and oxygen uptake (P < 0.05), and net uptake of amino acids [which was significant (P < 0.05) for valine and phenylalanine] by the LR3IGF-I-infused skin was increased. Total uptake of phenylalanine for skin protein synthesis, measured using [3H]phenylalanine uptake, was also significantly increased after 4 and 24 h of infusion. After 48 h of infusion all LR3IGF-I-dependent measurements of metabolic parameters had fallen to preinfusion values. By day 7 of the 21-day infusion there was a significant (P < 0.05) decrease in circulating endogenous IGF-I in plasma of treated sheep compared with that of control sheep, followed by a significant (P < 0.05) increase between day 7 and 21. Plasma insulin levels followed a similar pattern. There was no change at any stage of infusion in IGF-binding proteins in the plasma of the two LR3IGF-I-infused sheep tested, and it is concluded that LR3IGF-I caused a down-regulation of the type-I IGF-I receptors followed by a rise in endogenous IGF-I concentration consequent on lack of feedback regulation. After 21 days of infusion there was no effect of LR3IGF-I on wool-follicle-bulb-cell mitotic rate, bulb diameter or wool production.(ABSTRACT TRUNCATED AT 400 WORDS)