Low vitamin D levels increase the risk of type 2 diabetes in older adults: A systematic review and meta-analysis

Low serum levels of 25 hydroxyvitamin D (25OHD) (hypovitaminosis D) is common in older adults and associated with several negative outcomes. The association between hypovitaminosis D and diabetes in older adults is equivocal, however. We conducted a meta-analysis investigating if hypovitaminosis D is associated with diabetes in prospective studies among older participants. Two investigators systematically searched major electronic databases, from inception until 10/07/2016. The cumulative incidence of diabetes among groups was estimated according to baseline serum 25OHD levels. Random effect models were used to assess the association between hypovitaminosis D and diabetes at follow-up. From 4268 non-duplicate hits, 9 studies were included; these followed 28,258 participants with a mean age of 67.7 years for a median of 7.7 years. Compared with higher levels of 25OHD, lower levels of 25OHD were associated with a higher risk of developing diabetes (6 studies; n = 13,563; RR = 1.31; 95% CI: 1.11-1.54; I2 = 37%). The findings remained significant after adjusting for a median of 11 potential confounders in all the studies available (9 studies; n = 28,258; RR = 1.17; 95% CI: 1.03-1.33; p = 0.02; I2 = 0%). In conclusion, our data suggest that hypovitaminosis D is associated with an elevated risk of future diabetes in older people. Future longitudinal studies are required and should seek to confirm these findings and explore potential pathophysiological underpinnings.