Factors associated with low vitamin D in infants at four months

Background: Factors associated with vitamin D status in young infants are poorly described. Although breastfeeding is often considered a risk factor for vitamin D deficiency, the true culprit may be lack of supplementation in breastfed infants, not breastfeeding. In our study period, the American Academy of Pediatrics recommended all infants receive 200 IU/day of supplemental vitamin D. Formula fed infants traditionally receive the supplement in their formula; breastfed infants take a separate, oral supplement. Objective: To determine factors associated with vitamin D deficiency in infants at 4 months. Design/Methods: From 2004-2007, we enrolled 193 full-term, healthy infants at birth and followed them until 4 months of age. Primary outcome measure was 25(OH)D status at 4 months. In accordance with 2003 AAP guidelines, we considered infants adequately supplemented if, at 2 months (1) they were exclusively or mostly breastfed, prescribed a vitamin D supplement, and took the supplement >5 times a week; or (2) they consumed >500 ml/day of vitamin D fortified formula. Results: Median infant 25(OH)D at 4 months was 35.2 ng/ml; 12% of infants were deficient [25(OH)D <20 ng/ml]. Accurate supplementation data were available on 175 infants: 47% consumed all or mostly formula; 19% breastfed with appropriate supplementation, and 34% breastfed with inappropriate supplementation (no supplement prescribed, or supplement given <5 times/week). Supplemented breastfed infants were no more likely to be deficient than formula fed infants (p=0.91). Inappropriately supplemented infants were almost 18 times as likely to be deficient as supplemented infants (AOR=17.5; 95% CI 4.28-71.4). Increasing gestational age (AOR 0.41; 95% CI 0.23-0.76) and spending 10 minutes outside, at least once a week, (AOR=0.23; 95% CI 0.06-0.87) protected against deficiency. Living through fall or winter was a risk factor for deficiency. (AOR=3.89; 95% CI 1.06 -14.3). Vitamin D status at birth and skin color were not associated with deficiency at 4 months. Conclusions: Novel findings included a strongly protective association between increasing gestational age and vitamin D status at 4 months, and a lack of association between vitamin D status at birth and 4 months. Inappropriate supplementation was the main predictor of deficiency, but appropriately supplemented breastfed infants were no more likely to be deficient than formula fed infants.