Original ArticlesMaternal Obesity, 25-Hydroxy Vitamin D Concentration, and Bone Density in Breastfeeding Dyads

ObjectiveTo examine the association between maternal body mass index (BMI) and serum 25-hydroxy vitamin D [25(OH)D] concentration and bone density in mother-infant pairs.Study designThe study was a secondary analysis of 234 exclusively breastfeeding dyads who were recruited in the first postpartum month for a randomized controlled trial of maternal vs infant vitamin D supplementation. Mean 25(OH)D concentrations and bone mineral density (BMD) were compared by BMI group. The adjusted association between maternal BMI and 25(OH)D and bone density was examined at 1, 4, and 7 months postpartum.ResultsObese breastfeeding women had lower 25(OH)D concentrations and higher BMD than lean women at all 3 time points (P  <  .01). Higher maternal BMI was associated with lower maternal serum levels of 25(OH)D at 1, 4, and 7 months postpartum (adjusted β = −0.45 ng/ml per kg/m2, 95% CI −.076, −0.14, at 1 month) and higher BMD at the same time points (β = 0.006 BMD z score; 95% CI 0.003, 0.01 at 1 month). Seventy-six percent of infants were vitamin D deficient at 1 month of age. Infants born to overweight and obese mothers had lower 25(OH)D concentrations than infants of lean mothers (P < .01). For infants in the maternal supplementation group, higher maternal BMI was associated with lower 25(OH)D concentrations at 4 months (β = −0.68; 95% CI −1.17, −0.20) and lower bone density at 7 months (β = −0.001; 95% CI −0.002, −0.0001).ConclusionsIn exclusively breastfeeding dyads, maternal obesity is associated with lower maternal and infant serum 25(OH)D concentrations, which may impact infant bone density.Trial registrationClinicalTrials.gov: NCT00412074.