Low serum 25-hydroxyvitamin D level predicts progression to type 2 diabetes in individuals with prediabetes but not with normal glucose tolerance.

AIMS/HYPOTHESIS: Vitamin D deficiency may increase the risk of type 2 diabetes. We therefore investigated whether serum concentrations of 25-hydroxyvitamin D [25(OH)D] would predict the development of prediabetes (impaired fasting glucose, impaired glucose tolerance or the two combined) and type 2 diabetes, either on their own or when combined with serum concentrations of IGF-1 or IGF-binding protein-1 (IGFBP-1), which may interact with 25(OH)D. METHODS: At baseline, participants aged 35-56 years without known type 2 diabetes were examined using OGTTs, 25(OH)D and IGF peptide measurements, and anthropometric and lifestyle data. Participants who had prediabetes or type 2 diabetes at follow-up 8-10 years later were selected as cases; these were then age- and sex-matched to controls with normal glucose tolerance (NGT) at both baseline and follow-up, giving a total of 980 women and 1,398 men. RESULTS: Men but not women in the highest quartile of 25(OH)D level had a decreased OR for developing type 2 diabetes after adjustment for confounders (OR 0.52, 95% CI 0.30, 0.90), an effect accounted for by individuals with prediabetes, but not with NGT, at baseline. In both sexes, progression from prediabetes to type 2 diabetes was reduced by about 25% per 10 nmol/l increase in 25(OH)D. A high IGFBP-1 value was a better predictor of a reduced risk of type 2 diabetes than high 25(OH)D for both sexes, whereas high IGF-1 concentrations predicted a decreased risk only in men. CONCLUSIONS/INTERPRETATION: High serum 25(OH)D concentrations predict a reduced risk of type 2 diabetes in individuals with prediabetes, but not NGT. There were no significant interactions between 25(OH)D and IGFBP-1 or IGF-1 in terms of risk of diabetes. Our data suggest that vitamin D supplementation should be evaluated for the prevention of type 2 diabetes in prediabetic individuals.

Oral contraceptive use and abnormal glucose regulation in Swedish middle aged women.

AIM: To investigate the association between oral contraceptive (OC) use and abnormal glucose regulation in Swedish middle aged women. METHODS: A prospective population-based study including 4794 women, aged 36-56 at baseline. None had previously diagnosed diabetes. At both baseline and follow-up 8 years later, the women were examined by oral glucose tolerance test. Information regarding lifestyle factors and anthropometric measurements were collected. RESULTS: At baseline, current use of OCs was associated with pre (Odds ratio, OR 4.1, 95%CI 2.2-7.8) but not with type 2 diabetes. The association to prediabetes was entirely linked to IGT (OR 7.1, 3.3-15.8) in current users of OCs and in former users (OR 2.1, 1.1-3.9). Women who used OC at baseline had a better cardiovascular disease risk profile; lower body mass index (BMI), more physically active and less smoking. At follow-up, the increased risk did not persist. CONCLUSION: Current use of OC was associated with a four times increased risk of having prediabetes and seven times of having impaired glucose tolerance. No increased risk persisted at the follow-up, suggesting that the risk due to prior use of OC is decreasing with time. The healthier lifestyle in women who used OCs may have contributed to reduced long-term risk of prediabetes.