Milk mid-chain fatty acids and vitamin D supplementation are associated with prevalence of exclusive breastfeeding in Bangladeshi mothers

Exclusive breastfeeding in the first 6 months of life is crucial for the health of mothers and babies in low-and middle-income countries (LMIC). Milk mid-chain fatty acids (MCFA) are potential biomarkers of milk production in other settings. This study investigates MCFA as markers of exclusive breastfeeding in an LMIC. This was an ancillary observational analysis of human milk fatty acids from a parent randomized-controlled trial (RCT) of vitamin D supplementation in Bangladesh. We categorized mothers as currently exclusively or non-exclusively breastfeeding based on weekly infant feeding questionnaires. We analyzed milk fatty acids at 3 months postpartum by gas chromatography and modeled longitudinal exclusive breastfeeding using milk fatty acids in repeated measures Poisson regression. Fatty acids are reported as % total fatty acids. The prevalence of currently exclusive breastfeeding was 76% at 3 months and 43% at 6 months (N=587). Both C6:0 and C15:0 were higher with exclusive breastfeeding (C6:0, p=0.001; C15:0, p=0.007), while C12:0 and C14:0 were lower (C12:0, p<0.001; C14:0, p<0.001). We combined these into a MCFA index defined as ((C6:0+C15:0)/(C12:0+C14:0))*1,000 (Excl:25±0.50, Non-excl:20±0.60, p<0.001). Mothers in the highest and lowest MCFA index tertiles had an exclusive breastfeeding prevalence at 3 months of 95% and 60%, respectively (p<0.001) and remained different until 6 months. In secondary analysis, vitamin D supplementation during lactation was moderately associated with exclusive breastfeeding (relative prevalence: 1.17 [95% CI:1.04,1.32]). Milk MCFA were markers of exclusive breastfeeding in this cohort, and the milk MCFA index at 3 months predicted exclusive breastfeeding from 3 to 6 months postpartum.