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 N ew Z ealand ( 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 E uropean, 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‐ E uropean 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.