In January 2016 researchers from Denmark published the results of their study to assess vitamin D levels in breast milk during the first 9 months of breast-feeding. Blood and breast milk samples were taken from 107 mothers at 2 weeks, 90 mothers at 4 months and 48 mothers at 9 months post-partum and vitamin D levels assessed. Results showed that vitamin D levels in breast milk decreased during follow-up which was attributable to a decrease in the number of women taking vitamin D supplements, or the use of a lower dose in women taking supplements. Vitamin D levels were also seen to be generally higher in summer than in winter. Analysis showed that breast milk provided newborns with a vitamin D intake of under 20% as recommended by the Institute of Medicine. The researchers therefore concluded that exclusively breastfed infants should receive vitamin D supplements to reduce the risk of developing nutritional rickets.
við Streym S et al. Vitamin D content in human breast milk: a 9-mo follow-up study. Am J Clin Nutr. 2016 Jan;103(1):107-14