MedWire News: Low serum 25-hydroxyvitamin D (25[OH] D) is associated with an increased risk for Type 2 diabetes, suggest Norwegian researchers.
Guri Grimes (University Hospital of North Norway, Tromsø) and colleagues say: "The inverse relationship between serum 25(OH)D and body mass index (BMI)... is generally believed to be due to sequestration and/or storage of vitamin D and its metabolites in fat tissue.
"Much of the association between serum 25(OH)D and subsequent Type 2 diabetes is mediated through BMI."
In 1994-1995, the team measured the serum 25(OH)D levels of 6119 participants without diabetes who were aged 25 years or older.
Given the suggestion of a link between smoking and low serum 25(OH)D levels by previous studies, Grimes et al assigned the participants to sub-groups according to their smoking status: non-smokers (including former smokers, n=4157) and smokers (n=1962).
Serum 25(OH)D levels were arranged into quartiles, and the incidence of diabetes among the participants over an 11-year follow-up period was observed.
The findings, reported in the journal Diabetic Medicine, showed that by 2005, 183 (4.4%) non-smokers and 64 (3.3%) smokers had developed diabetes.
Compared with non-smokers in the fourth (highest) quartile for serum 25(OH)D, the hazard ratios (HRs) for incident diabetes during follow-up among non-smokers in the third, second, and first (lowest) quartiles were 1.00, 1.50, and 1.89, respectively, after adjustment for age and gender.
The risk for diabetes associated with each increasing quartile appeared to be much greater among the smokers than non-smokers. Indeed, the corresponding HRs for incident diabetes were 1.79, 2.33, and 2.68, respectively, among smokers.
Of note, the team also found a 14% and 15% reduction in risk for developing diabetes per 10 nmol/l increase in serum 25(OH)D among non-smokers and smokers, respectively (p<0.01).
After adjustment for BMI, the association between serum 25(OH)D and diabetes development decreased and became nonsignificant.
Grimes et al conclude: "Long-term randomized control trials, as well as prospective follow-up studies from a young age, using repeated serum 25(OH)D measurements, are needed to assess the possible role of vitamin D status over time and of long-term vitamin D supplementation in the prevention of Type 2 diabetes."
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