Background: Maternal milk-borne transforming growth factor (TGF-β plays a potential role in the development of the mucosal immune system in infants. However, it remains unclear what factors determine TGF-β levels in breast milk. We hypothesized that microbial pressures during pregnancy might affect the expression levels of TGF-β in colostrum.
Objective: This study compared TGF-β2 levels in colostrum of lactating women living in Japan and Nepal with contrasting hygiene statuses. Additionally, we identified environmental and intrinsic factors influencing TGF-β levels in colostrum.
Methods: Breast milk samples and structured questionnaires were collected from 80 women living in Japan and 208 women living in Nepal. A robust regression model was used to identify factors associated with colostral TGF-β levels.
Results: Analysis using the Mann-Whitney U test showed that TGF-β levels were significantly higher in Japanese women than in Nepalese women. Japanese women who consumed animal milk daily during pregnancy and had atopic dermatitis expressed lower levels of TGF-β in colostrum, as compared to Japanese women who did not. Among Nepalese women, large family size and higher birth order were associated with lower TGF-β levels and women who gave birth to infants with low birth weight had higher expression of TGF-β levels in milk than women who gave birth to infants with normal birth weight.
Conclusion: The results suggest that induction of TGF-β levels in colostrum depends on differences in the ethnicity of lactating women. Consumption of animal protein and parturition characteristics may affect TGF-β levels in breast milk, and may explain differences in these levels in breast milk between countries.