Vitamin C and the risk of gestational diabetes mellitus: a case-control study.

Objective: To examine whether low maternal dietary intake of vitamin C and low maternal plasma ascorbic acid (AA) concentrations are associated with an increased risk of gestational diabetes mellitus (GDM).

Methods: Cases were 67 women with GDM meeting National Diabetes Data Group criteria. Controls were 260 women without such a diagnosis. Maternal dietary vitamin C consumption during the periconceptional period and during pregnancy was assessed using a 121-item, semiquantitative food frequency questionnaire. Maternal plasma AA concentrations were determined using automated enzymatic procedures on specimens collected during the intrapartum period.

Results: Mean maternal daily consumption of vitamin C and plasma AA concentrations were 10% and 31% lower, respectively, among GDM cases as compared with controls (130.7 +/- 10.2 vs. 145 +/- 4.9 mg/d, P = .190; 36 +/- 2.0 vs. 53 +/- 1.0 micromol/L, P <.001). After controlling for maternal age, race, prepregnancy adiposity, family history of type 2 diabetes, energy intake and income, women reporting low daily vitamin C intake (< 70 mg/d), as compared with the other women, experienced a 3.7-fold increased risk of GDM (odds ratio [OR] = 3.7, 95% confidence interval [CI] 1.7-8.2). There was a linear relation in risk of GDM with decreasing concentrations of plasma AA (P for linear trend <.001). After adjusting for confounders, women in the lowest quartile (< 42.6 micromol/L), as compared with women in the highest quartile (> 63.3 micromol/L), experienced > 12-fold increased risk of GDM (OR = 12.8, 95% CI 3.5-46.2).

Conclusion: Low maternal dietary vitamin C intake and low plasma AA concentrations are associated with an increased risk of GDM. Large, prospective, cohort studies are needed to further evaluate the potential beneficial role of vitamin C and other antioxidants in the prevention of impaired glucose tolerance in pregnancy.