Plasma vitamin D status in patients with type 2 diabetes with and without retinopathy

Objective Diabetic retinopathy (DR) is a common cause of blindness. Although an association between hypovitaminosis D and type 1 diabetes is known, the association between vitamin D (VD) and type 2 diabetes (T2D) and its complications such as DR has been unclear. The aim of this study was to investigate the status of VD in T2D patients with and without DR. Methods A cross-sectional case–control study was conducted with 99 normal control (CN) participants and 164 patients with T2D, of which 82 had retinopathy (DR) and 82 did not (DNR). After a complete ophthalmic examination, inclusive of fundus fluorescein angiography, the clinical profile and the plasma levels of VD and calcium were analyzed. Results Although the mean plasma VD levels were significantly lower in the DNR and DR groups compared with the CN group, no significant differences were observed between the groups with diabetes. Although the mean levels of VD in all three groups were below the normal range, the prevalence of VD deficiency (VDD) was higher in the DNR and DR groups (66% and 63%) than in the CN group (45%), suggesting that the prevalence of VDD was higher in individuals with diabetes, regardless of the presence or absence of retinopathy. However, there were no group differences in the plasma levels of calcium. Additionally, VDD did not seem to be related to patient's age or body mass index, but was related to the duration of diabetes. Conclusion Results from this study suggest a possible association between VDD and T2D, but not specifically with DR. Further investigations are warranted.