Determinants of vitamin D status in pregnant women and neonates.

OBJECTIVES: Evidence suggests a beneficial effect of vitamin D on perinatal health; however, low vitamin D status is prevalent in pregnant women and neonates. The objective was to determine factors that are associated with vitamin D status of mothers in early pregnancy and neonates.

METHODS: The study comprised 1,635 pregnant women from Quebec City and Halifax, Canada, 2002-2010. Vitamin D status was based on the concentration of 25-hydroxy-vitamin D [25(OH)D] determined with a chemiluminescence immunoassay in maternal sera collected at a median of 15 weeks' gestation and in neonatal cord sera at delivery. A questionnaire with information on potential determinants was completed midpregnancy.

RESULTS: A total of 44.8% of mothers and 24.4% of neonates had 25(OH)D concentrations <50 nmol/L. Adjusted mean (95% confidence interval) maternal 25(OH)D levels were higher in summer than in winter by 16.1 nmol/L (13.6-18.7), and in those in the highest versus the lowest category of education by 6.1 nmol/L (0.5-11.8), in BMI <25 kg/m2 versus BMI ≥35 kg/m2 by 8.2 nmol/L (4.0-12.3), and in the highest versus the lowest physical activity category by up to 9.5 nmol/L (2.9-16.1). Determinants of neonatal 25(OH)D levels were similar but also included maternal age, dairy intake, supplement use and 25(OH)D level.

CONCLUSION: This study suggests that vitamin D status of pregnant women and/or neonates might be improved through supplementation, adequate dairy intake, a move towards a healthy pre-pregnancy body weight, and participation in physical activity. Controlled studies are needed to determine the effectiveness of interventions aimed at these factors.