The Association Between Total Duration of Breastfeeding and Serum 25-Hydroxyvitamin D

BACKGROUND: Breastfed infants are at increased risk for developing vitamin D deficiency and rickets due to minimal vitamin D in breast milk. While previous research supports the association between exclusive breast-feeding and vitamin D deficiency, little is known about the effect of total duration of breastfeeding, which includes both the periods of exclusive breastfeeding and after the introduction of complementary foods, on vitamin D status. OBJECTIVES: To determine whether total duration of breastfeeding is associated with serum 25-hydroxyvitamin D (25-OHD) level in early childhood and to explore the effect of vitamin D supplementation on the relationship between total duration of breastfeeding and vitamin D status. DESIGN/METHODS: A cross-sectional study of healthy children seen for primary health care between September 2011 and August 2013 was conducted through the TARGet Kids! practice-based research network. Adjusted linear regression was used to determine the association between total duration of breastfeeding and serum 25-OHD and to explore the effect of vitamin D supplementation. Adjusted logistic regression was used to assess the probability of 25-OHD <20 ng/mL in supplemented vs. non-supplemented children. RESULTS: An association that was modified by vitamin D supplementation was identified between total duration of breastfeeding and serum 25-OHD (P=0.0251). Every one month increase in total duration of breastfeeding was associated with a 0.11 ng/mL lower median serum 25-OHD level (95% CI −0.20, −0.02 ng/mL) among children who were not supplemented. The odds of serum 25-OHD