Serum Vitamin D and Subsequent Occurrence of Type 2 Diabetes

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Abstract
Low vitamin D status has been suggested as a risk factor for type 2 diabetes. Although the epidemiologic evidence is scarce, 2 recent studies have suggested an association. The present study investigated the relation of serum vitamin D with type 2 diabetes incidence using pooled data from these 2 cohorts. Two nested case-control studies, collected by the Finnish Mobile Clinic in 1973–1980, were pooled for analysis. The study populations consisted of men and women aged 40–74 years and free of diabetes at baseline. During a follow-up period of 22 years, 412 incident type 2 diabetes cases occurred, and 986 controls were selected by individual matching. Serum vitamin D (serum 25(OH)D) was determined from frozen samples, stored at baseline. Pooled estimates of the relationship between serum vitamin D concentration and type 2 diabetes incidence were calculated. Men had higher serum vitamin D concentrations than women and showed a reduced risk of type 2 diabetes in their highest vitamin D quartile. The relative odds between the highest and lowest quartiles was 0.28 (95% confidence interval = 0.10–0.81) in men and 1.14 (0.60–2.17) in women after adjustment for smoking, body mass index, physical activity, and education. The results support the hypothesis that high vitamin D status provides protection against type 2 diabetes. Residual confounding may contribute to this association.