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Keywords:

  • Diabetes;
  • insulin sensitivity;
  • obesity;
  • vitamin D

Eur J Clin Invest 2011; 41 (11): 1195–1201

Abstract

Background  Both obesity and type 2 diabetes are associated with hypovitaminosis D. We investigated the impact of body mass index (BMI) status on the relationship of serum 25-hydroxyvitamin D (25OHD) concentration with insulin sensitivity.

Design  This cross-sectional study enrolled 126 healthy and glucose-tolerant subjects. The participants were divided into two groups based on BMI: normal weight (n = 68) and overweight (n = 58). Insulin sensitivity index (ISI) and beta-cell function were assessed by using hyperglycaemic clamps. Serum 25OHD concentration was determined in the fasting samples.

Results  The correlation of serum 25OHD with ISI was much stronger in the overweight group (r = 0·5271, P < 0·0001) than in the normal weight group (r = 0·2836, P = 0·002). The correlation remained significant in the overweight group (r = 0·3620, P = 0·002), but not in normal weight group after adjusting for age, gender, BMI, season of study, ethnicity and exercise. Nonlinear regression analysis revealed that when serum 25OHD concentration was > 40 ng mL−1, the association between serum 25D concentrations and insulin sensitivity plateaued.

Conclusions  We observed stronger associations of serum 25OHD with insulin sensitivity in overweight than normal weight subjects, suggesting that overweight subjects with hypovitaminosis D may benefit more from vitamin D replacement than normal weight subjects. Furthermore, the optimal serum 25OHD concentration for insulin sensitivity is about 40 ng mL−1. As more than 60% of the US population is overweight and hypovitaminosis D is highly prevalent in overweight subjects, hypovitaminosis D has a large population attributable risk for type 2 diabetes.