Vitamin D status among 4-month-old infants in New England: a prospective cohort study.

Background: Concerns over vitamin D deficiency in infants and children recently prompted the American Academy of Pediatrics to recommend increased supplementation. Few studies have examined vitamin D status in the same infants over time. Also, while many researchers label "breastfeeding" as a risk factor for vitamin D deficiency, few differentiate between any breastfeeding, exclusive breastfeeding, and supplemented or unsupplemented breastfeeders. Objective: To determine predictors of 25(OH) D deficiency at 4 months in a group of children previously tested at birth. Methods: We enrolled newborns from 2005 to 2007 at an urban Boston hospital. Maternal and infant blood samples were collected within 72 hours of birth. At 4 months, we obtained a second infant blood sample. Results: At 4 months, 11.9% of the 177 infants were vitamin D deficient compared to 37.5% at birth (25(OH) D < 20 ng/mL). Median 25(OH) D was 35.2 ng/mL (range, 5-100.8; 95% confidence interval [CI], 32.8-37.6). At 4 months, 40% of unsupplemented infants were deficient. Lack of supplementation was significantly associated with increased risk of deficiency (adjusted odds ratio [AOR], 19.3; 95% CI, 4.80-77.2). Being outside at least 10 minutes a day, once per week, was protective (AOR, 0.12; 95% CI, 0.02-0.66), as was increasing gestational age (AOR, 0.36; 95% CI, 0.19-0.69). In 48.4% of patients, physicians failed to prescribe vitamin D at 2 months. Conclusions: Despite inconsistent supplementation, a smaller proportion of infants were vitamin D deficient at 4 months than at birth. While supplemented breastfed infants were not at risk of deficiency, unsupplemented exclusively breastfed infants were at high risk of severe deficiency.