Do maternal dietary vitamin D intake and sunlight exposure affect the vitamin D status of exclusively breastfed infants?

Aim: Exclusively breastfed infants are dependent upon their mothers for their vitamin D intake. In New Zealand (NZ), vitamin D supplementation is not routinely recommended for exclusively breastfed infants. We aimed to determine the association of exogenous maternal vitamin D intake and sunlight exposure with serum 25-hydroxyvitamin D [25(OH) D] concentration in exclusively breastfed infants aged 2-3 months. Methods: We enrolled a convenience sample of women and their exclusively breastfed infants. Maternal dietary and supplemental vitamin D intake was determined from an interviewer-administered semi-quantitative food frequency questionnaire. Sunlight exposure was determined from reported time spent outdoors. Associations of vitamin D intake and sunlight exposure with infant serum 25(OH) D concentration at age 2-3 months were determined using multivariable linear regression. Results: Sixty-three mother-infant pairs, 73% of whom were European, and their exclusively breastfed infants completed the study. Mean (SD) serum 25(OH) D concentration was 52 nmol/L (30), with 28% of infants being vitamin D deficient (25(OH) D < 50 nmol/L). Estimated median maternal dietary vitamin D intake from food was 158 IU/day. Thirty (48%) mothers consumed vitamin D supplements. Non-European ethnicity (P = 0.01) and measurement of 25(OH) D during winter (P < 0.001) were independently associated with infant serum 25(OH) D concentration. Maternal dietary vitamin D intake (P = 0.62), supplement use (P = 0.32) and sunlight exposure (P = 0.72) were not independently associated with infant serum 25(OH) D concentration. Conclusions: Serum 25(OH) D concentrations in exclusively breastfed infants in NZ are independent of current maternal vitamin D intake and sunlight exposure practices. Consideration needs to be given for vitamin D supplementation of exclusively breastfed infants during winter.