Prenatal vitamin use and vitamin D status during pregnancy, differences by race and overweight status.

OBJECTIVE: We aimed to study whether prenatal vitamin (PNV) use protects against low 25-hydroxyvitamin D (25[OH]D) levels in all women and particularly in obese and black women who are both at risk of vitamin D deficiency and poor pregnancy outcomes.

STUDY DESIGN: We studied 1019 women enrolled in a prospective study at Brigham and Women's Hospital in Boston, from 2007 to 2009. We used multivariable logistic regression to analyze associations of PNV use and odds of vitamin D deficiency defined as 25[OH]D levels <50 nmol l(-1).

RESULT: In all, 56% of black and 86% of white women reported pre- and/or postconceptional PNV use. In the first trimester, 75% of black and 19% of white women were vitamin D deficient. Lack of PNV use among black women was not associated with vitamin D deficiency (adjusted odds ratio (OR) 1.0, 95% confidence interval (CI) 0.4, 2.3) but was among white women (OR 3.5, 95% CI 2.1, 5.8) (interaction P<0.01).

CONCLUSIONS: Ongoing trials of vitamin D supplementation during pregnancy should consider potential effect modification by race/ethnicity.