ABSTRACT
BACKGROUND: Conflicting results currently exists on the association between vitamin D and glucose metabolism. The role of maternal vitamin D status in gestational diabetes mellitus (GDM) is not clear. This meta-analysis aimed to examine this role in women with GDM compared with normal glucose tolerance (NGT). METHODS: We performed a systematic review and meta-analysis by searching MEDLINE database, the Cochrane library and Uptodate® Online for English-language literature up to September 2011. Summary odds ratios were calculated using a random-effects model meta-analysis. RESULTS: Seven observational studies were eligible for the meta-analysis, including 2146 participants of whom 433 were diagnosed with GDM. Four studies reported a high incidence of vitamin D deficiency in pregnant women (>50%). Overall vitamin D deficiency (serum 25-hydroxyvitamin D (25OHD)<50 nmol/l) in pregnancy was significantly related to the incidence of GDM with an odds ratio of 1.61 (95% CI 1.19-2.17; p=0.002). Serum 25OHD was significant lower in participants with GDM than in those with NGT (-5.33 nmol/l (95% CI -9.73 to -0.93; p=0.018). CONCLUSIONS: This meta-analysis indicates a significant inverse relation of serum 25OHD and the incidence of GDM. However, it remains unclear whether this association is causal due to the observational study design of the studies. Clinical trials are needed to examine whether vitamin D supplementation will improve glycemic control in women with GDM.