Serum 25(OH)D and incident type 2 diabetes: a cohort study.

BACKGROUND/OBJECTIVES: Mild to moderate vitamin D insufficiency has been proposed as a risk factor for several common chronic diseases including type 2 diabetes. This study aimed to examine the association between serum 25-hydroxy vitamin D (25(OH)D) and incident diabetes.

SUBJECTS/METHODS: The MONICA10 cohort consists of 2656 participants (men and women aged 41-71 years) who participated in a 10-year follow-up examination during 1993-1994 as part of the MONICA 1 population survey. A total of 2571 participants free of diabetes at baseline and with successful measurement of serum 25(OH)D were included in the current study. The Danish National Diabetes register enabled identification of 288 cases of incident diabetes during follow-up (median: 16.4 years). Data were analysed by Cox proportional hazard models and associations were expressed as hazard ratios (HRs) with 95% confidence intervals (CIs).

RESULTS: Serum 25(OH)D was inversely associated with incident diabetes adjusted for potential confounders (HR per 25 nmol/l=0.83; 95% CI: 0.72-0.95; P=0.009). A statistically significant interaction was observed between 25(OH)D and waist circumference (WC) (P(interaction)=0.042) suggesting an association in persons with a high WC (HR (95%CI) per 25 nmol/l=0.74 (0.63-0.88), 218 incident cases) and not in persons with a normal WC (HR (95%CI) per 25 nmol/l=0.98 (0.78-1.24), 70 incident cases).

CONCLUSIONS: Low serum 25(OH)D was associated independently with incident diabetes. The inverse association was only found in overweight-obese and not in normal weight individuals, suggesting that obesity may modify the effect of vitamin D status on the risk of diabetes.