Lower levels of 25-hydroxyvitamin D-3 are associated with a higher prevalence of microvascular complications in patients with type 2 diabetes

Objective: Low levels of serum 25-hydroxyvitamin D [25(OH) D] are commonly found in type 2 diabetes. We examined whether there is an association between circulating 25(OH) D concentrations and the presence of microvascular complications in people with type 2 diabetes. Research design and methods: We studied 715 outpatients with type 2 diabetes who regularly attended our clinic. Participants were evaluated for the presence of microvascular complications (namely retinopathy and/or nephropathy) by clinical evaluation, fundus examination, urine examination and biochemical tests. Serum 25(OH)D levels were also measured for each participant. Results: Hypovitaminosis D (ie, a serum 25(OH) D level <30 ng/mL) was found in 75.4%, while deficiency (ie, a 25(OH) D level <20 ng/mL) was found in 36.6% of these patients. Serum 25(OH) D levels decreased significantly in relation to the severity of either retinopathy or nephropathy or both. In multivariate logistic regression analysis, lower 25(OH) D levels were independently associated with the presence of microvascular complications (considered as a composite end point; OR 0.758; 95% CI 0.607 to 0.947, p=0.015). Notably, this association remained significant even after excluding those with an estimated glomerular filtration rate <60 mL/min/1.73 m(2). Conclusions: We found an inverse and independent relationship between circulating 25(OH)D levels and the prevalence of microvascular complications in patients with type 2 diabetes. However, vitamin D may be simply a marker and causality cannot be implied from our cross-sectional study. Whether vitamin D supplementation in patients with type 2 diabetes may have beneficial effects on the risk of microvascular complications remains to be investigated.