Background: Vitamin D insufficiency and type 2 diabetes are both common in Finland, and low vitamin D status has been suggested as a risk factor for type 2 diabetes. Our aim was to study the associations between serum 25-hydroxyvitamin D [25(OH)D], a marker of vitamin D status, and glucose homeostasis and type 2 diabetes in a general population sample in Eastern Finland.

Methods: Cross-sectional analysis in the Kuopio Ischaemic Heart Disease Risk Factor Study. A total of 850 men and 906 women, aged 53-73 years, were analysed. Relative risk (RR) of prevalent diabetes was estimated as odds ratios by logistic regression. Associations between serum 25(OH)D and markers of impaired glucose metabolism in tertiles of serum 25(OH)D concentration were assessed by linear regression.

Results: The mean serum 25(OH)D concentration was 43.4 nmol/L (SD 17.6, range 8.5-122.8 nmol/L) in the study population. Serum 25(OH)D concentration <50 nmol/L were observed in 65.5% of the participants. Serum 25(OH)D was inversely associated with fasting serum insulin, fasting blood glucose and oral glucose tolerance test (OGTT) 2-h glucose levels after adjustment for age, gender and examination year. Association with the OGTT 2-h glucose remained statistically significant after multivariate adjustments. The RR (95% confidence interval) for type 2 diabetes in tertiles of serum 25(OH)D were 1, 1.26 (0.86, 1.85) and 1.44 (0.96, 2.15) after multivariate adjustments (p for trend = 0.08).

Conclusions: Our results suggest that low serum 25(OH)D is associated with impaired glucose and insulin metabolism.