Early pregnancy maternal vitamin D concentrations and risk of gestational diabetes mellitus.

BACKGROUND: While associations of vitamin D deficiency with type 2 diabetes have been well demonstrated, investigations of vitamin D and risk of gestational diabetes mellitus (GDM) reported inconsistent findings. We examined associations of vitamin D status with GDM.

METHODS: In a nested case-cohort study (135 GDM cases and 517 non-GDM controls), we measured maternal serum vitamin D status (total 25[OH]D and 25[OH]D3 ) in early pregnancy (16 weeks on average) using liquid chromatography-tandem mass spectroscopy. GDM was diagnosed according to the American Diabetes Association guidelines. We calculated adjusted odds ratios and 95% confidence intervals (CIs) using logistic regression models.

RESULTS: GDM cases had lower mean total 25[OH]D (27.3 vs. 29.3 ng/mL) and 25[OH]D3 (23.9 vs. 26.7 ng/mL) concentrations compared with women who did not develop GDM (both P-values < 0.05). Overall, 25[OH]D3 concentrations, but not total 25[OH]D concentrations, were significantly associated with GDM risk. A 5-ng/mL increase in 25[OH]D3 concentration was associated with a 14% decrease in GDM risk (P-value = 0.02). Women in the lowest quartile for 25[OH]D3 concentration had a twofold [95% CI 1.15, 3.58] higher risk of GDM compared with women in the highest quartile (P-value for trend < 0.05).

CONCLUSIONS: Early pregnancy vitamin D status, particularly 25[OH]D3 , is inversely associated with GDM risk.