Abstract

t has been suggested that vitamin D reduces the risk of type 2 diabetes.The finding that vitamin D deficiency is associated with impaired ␤-cell function and insulin resistance in animals (1,2) and humans (3,4) is in line with that hypothesis.In the only cohort study publ i s h e d , t h e i n t a k e o f v i t a m i n D supplements was inversely associated with the development of type 2 diabetes (5).Since vitamin D intake covers only a part of the total vitamin D available, the purpose of this study was to evaluate the prediction of serum 25-hydroxyvitamin D (25OHD) on subsequent type 2 diabetes incidence. RESEARCH DESIGN AND METHODS -The study population, collected from 1978 to 1980 as part of the Mini-Finland Health Survey (6), consisted of 4,423 men and women aged 40 -69 years.After exclusion of 247 individuals with type 2 diabetes at baseline (i.e., fasting plasma glucose Ͼ7.0 mmol/l on two occasions or Ͼ11.0 mmol/l on a single occasion) and 79 individuals with missing values of serum 25OHD, the final sample size was 4,097.Data on education, smoking, leisure-time exercise, and hypertension medication were collected in a health examination (6).Height, weight, and blood pressure were measured, and blood samples were collected and stored at Ϫ20°C.In 2003-2004, radioimmunoassay ( 125 I RIA kit; DiaSorin, Stillwater, MN) was used to assess serum 25OHD in thawed samples.The coefficient of variation for serum 25OHD varied from 8 to 13%.During 17 years of