Relationship between total vitamin D metabolites and complications in patients with type 2 diabetes

In our previous study, it was shown that endogenous vitamin D3 and its metabolites are associated with diabetic microvascular complications and cardiovascular risk factors. The aim of the present study was to determine if the relationship between total vitamin D (vitamin D2 supplements plus endogenous vitamin D3) was a better predictor of complications in type 2 diabetes (T2DM). A total of 460 patients with T2DM participated in the present cross-sectional study. Plasma levels of total vitamin D and its metabolites (1,25-dihydroxyvitamin D (1,25(OH)D), 25-hydroxyvitamin D (25(OH)D) and 24,25-dihydroxyvitamin D (24,25(OH)D) were measured by isotope-dilution liquid chromatography tandem mass spectrometry analysis. 1,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 were associated with diabetic retinopathy and coronary artery disease, but total 1,25-dihydroxyvitamin D and total 25-hydroxyvitamin D levels were not statistically associated with any complications. Total 1,25-dihydroxyvitamin D showed the same positive association as 1,25-dihydroxyvitamin D3 for hypertension and dyslipidemia, and total 25-hydroxyvitamin D showed the same positive association as 25-hydroxyvitamin D3 for dyslipidemia. Total 24,25-dihydroxyvitamin D showed the same positive association only with dyslipidemia as did 24,25-dihydroxyvitamin D3. However, total 25-hydroxyvitamin D was associated with hypertension, whereas 25-hydroxyvitamin D3 was not. Vitamin D3 metabolites were associated with diabetic retinopathy, whereas total vitamin D levels were not, suggesting that endogenous vitamin D3 metabolites are a better measure of diabetic microvascular complications. However, both total vitamin D and vitamin D3 metabolites were associated with cardiovascular risk factors in patients with type 2 diabetes.