REVIEW: The Role of Vitamin D and Calcium in Type 2 Diabetes. A Systematic Review and Meta-Analysis

Context:Altered vitamin D and calcium homeostasis may play a role in the development of type 2 diabetes mellitus (type 2 DM). Evidence Acquisition and Analyses: MEDLINE review was con-ducted through January 2007 for observational studies and clinical trials in adults with outcomes related to glucose homeostasis. When data were available to combine, meta-analyses were performed, and summary odds ratios (OR) are presented. Evidence Synthesis: Observational studies show a relatively con-sistent association between low vitamin D status, calcium or dairy intake, and prevalent type 2 DM or metabolic syndrome [OR (95% confidence interval): type 2 DM prevalence, 0.36 (0.16–0.80) among nonblacks for highest vs. lowest 25-hydroxyvitamin D; metabolic syn-drome prevalence, 0.71 (0.57–0.89) for highest vs. lowest dairy in-take]. There are also inverse associations with incident type 2 DM or metabolic syndrome [OR (95 % confidence interval): type 2 DM inci-dence, 0.82 (0.72–0.93) for highest vs. lowest combined vitamin D and calcium intake; 0.86 (0.79–0.93) for highest vs. lowest dairy intake]. Evidence from trials with vitamin D and/or calcium supplementation suggests that combined vitamin D and calcium supplementation may have a role in the prevention of type 2 DM only in populations at high risk (i.e. glucose intolerance). The available evidence is limited be-cause most observational studies are cross-sectional and did not ad-just for important confounders, whereas intervention studies were short in duration, included few subjects, used a variety of formula-tions of vitamin D and calcium, or did post hoc analyses. Conclusions: Vitamin D and calcium insufficiency may negatively influence glycemia, whereas combined supplementation with both nutrientsmay be beneficial in optimizing glucosemetabolism. (JCli