Maternal Determinants of Human Milk Contamination in Heavy Metals: A Narrative Review

Human milk is the optimal nutrition for infants, and thus mothers are highly encouraged to breastfeed exclusively for 6 mo postdelivery. However, toxic heavy metals, to which mothers may be exposed, can be transferred into human milk, potentially increasing health risks for breastfed infants. It is crucial to investigate human milk contamination in toxic metals, its determinants in the mother's environment, and the associated health impacts from its consumption. This study aimed to summarize the available literature on the presence of heavy metals in human milk and the associated maternal sociodemographic and nutritional factors. We conducted a comprehensive search of PubMed, Scopus, ProQuest, Google Scholar, Cochrane, and Embase databases. The findings from 21 cross-sectional studies on human milk contamination with lead, cadmium, mercury, copper, and arsenic are included, including contamination levels and maternal dietary and lifestyle factors contributing to exposure. Studies revealed geographical variations in heavy metal contamination levels. Among dietary determinants, fish and seafood consumption was significantly associated with increased levels of heavy metals, especially in crabs and large fish. Moreover, both first and second-hand smoking emerged as major risk factors linked to maternal exposure. Despite these concerns, breastfeeding remains the preferred and optimal method for infant nutrition as its benefits outweigh its potential risks, especially since formula milk might contain higher levels of contaminants. Future research is required to examine levels of human milk contamination in other areas of the world and their link with different maternal environmental factors. These findings serve to guide health and food policies and awareness campaigns that can minimize the mother's exposure to these toxic metals.