Serum 25-hydroxyvitamin D and risk of type 2 diabetes in older adults: A dose–response meta-analysis of prospective cohort studies

Lower serum level of 25-hydroxyvitamin D is common in older adults and associated with several negative outcomes. However, previous studies have indicated that 25-hydroxyvitamin D is associated with risk of type 2 diabetes, but presented controversial results. Studies in PubMed and EMBASE were searched update to June 2017 to identify and quantify the potential dose–response association between low 25-hydroxyvitamin D and risk of type 2 diabetes in older adults. Nine eligible studies involving a total of 34,511 participants with 2863 incident cases were included in this meta-analysis. Our results showed statistically significant association between lower 25-hydroxyvitamin D and type 2 diabetes in older adults [odds ratio (OR) = 1.19, 95% confidence interval (95% CI): 1.08–1.32, P = .001]. In addition, we obtained the best fit at an inflection point of decrease 10 ng/mL in piecewise regression analysis; the summary relative risk of type 2 diabetes in older adults for a decrease of 10 ng/mL 25-hydroxyvitamin D was 1.06 (95% CI: 1.02–1.13, P < .001). Furthermore, subgroups analysis indicated that lower 25-hydroxyvitamin D was associated with a significant increment risk of type 2 diabetes in older adults in female (OR = 1.21, 95% CI: 1.04–1.40, P = .014) but not in male (OR = 1.11, 95% CI: 0.75–1.63, P = .615). Subgroup meta-analyses in study design, duration of follow-up, number of participants, and number of cases showed consistent with the primary findings. Lower 25-hydroxyvitamin D is associated with type 2 diabetes in older adults risk increment.