J-shaped relationship between waist circumference and subsequent risk for Type 2 diabetes: An 8-year follow-up of relatively lean Japanese individuals J-shaped relationship between waist circumference and subsequent risk for Type 2 diabetes : an 8-year follow-up of relatively lean Japanese individuals

Aims This study investigated the relationship between waist circumference and the subsequent incidence of Type 2 diabetes and the association with insulin resistance and pancreatic B-cell function in relatively lean Japanese individuals. Methods The study participants were 3992 employees (2533 men and 1459 women, aged 35-55 years) of a metal-products factory in Japan. The incidence of diabetes was determined in annual medical examinations during an 8-year follow-up. We calculated age- and sex-adjusted hazard ratios (HRs) according to the sex-specific quintile of waist circumference at baseline. Differences in baseline insulin resistance [homeostatis model assessment (HOMA)-IR] and pancreatic B-cell function (HOMA-B) were compared between participants who developed diabetes and those who did not. Results During the follow-up, 218 participants developed diabetes. Age- and sex-adjusted HRs across the quintiles of waist circumference were 1.78, 1.00 (reference), 1.59, 3.11 and 3.30, respectively (P for trend, < 0.0001). The HR for the lowest quintile was significantly higher than that for the second quintile. Among participants with waist circumference of the lowest quintile, HOMA-B was lower in those who developed diabetes than in those who did not [33.1 (24.1-45.0) vs. 54.3 (37.9-74.6) median (interquartile range), P < 0.0001], but HOMA-IR did not differ between these groups. Conclusions There was a J-shaped relationship between waist circumference and subsequent risk for Type 2 diabetes in relatively lean Japanese individuals; lower pancreatic B-cell function may also increase the risk of diabetes in very lean Japanese people. © 2009 Diabetes UK.