Pre-pregnancy habitual intake of vitamin D from diet and supplements in relation to risk of gestational diabetes mellitus: a prospective cohort study

Background Vitamin D may play a pivotal role in regulating insulin secretion and insulin sensitivity. However, the impact of vitamin D intake either from diet or from supplements on the development of gestational diabetes mellitus (GDM) remains unknown. We prospectively examined the association of pre-pregnancy habitual intake of vitamin D from diet and supplements with risk of incident GDM in a well-established cohort. Methods We included 21,356 singleton pregnancies from 15,225 women in the Nurses' Health Study II cohort. Diet information, including vitamin D intakes from food sources and supplements, was assessed in 1991 and every four years thereafter by validated food frequency questionnaires. We used log-binomial models with generalized estimating equations to estimate the relative risks (RRs) and 95% confidence intervals (CIs). Results We documented 865 incident GDM cases during 10 years of follow-up. After adjustment for age, parity, race/ethnicity, family history of diabetes, dietary and lifestyle factors, and body mass index, the RRs (95% CIs) of GDM risk associated with supplemental vitamin D intake of 0, 1–399, ≥ 400 IU/d were 1.00 (reference), 0.80 (0.67-0.96), and 0.71 (0.56-0.90), respectively (P for trend = 0.002). Dietary and total vitamin D intakes were also inversely associated with GDM risk, but the associations were not statistically significant. Conclusions Pre-pregnancy supplemental vitamin D intake was significantly and inversely associated with risk of GDM. Our study indicates potential benefits of increasing vitamin D intake from supplements in the prevention of GDM in women of reproductive age