From mammary glands to nutrients: genetic insights into milk composition†

Lactation is a cornerstone of mammalian life, providing nutrient-rich milk that supports offspring growth and development. Breastfeeding offers immediate and long-term benefits for infant and maternal health, shaping life-course health outcomes and reducing disease risks. Milk is a complex and dynamic fluid containing nutrients and bioactive molecules, and its composition is affected by environmental and genetic factors. Research on human milk falls into two primary areas: its biochemistry, which explores milk composition, and epidemiology, which examines the impact of lactation and breastfeeding on health. Together, these fields provide insights into the function of milk components. However, the genetic mechanisms that determine and influence milk composition remain poorly understood. Most findings linking genetics and milk composition have emerged from agricultural studies, where the mechanistic understanding is limited. In-vivo studies focus on mammary gland development, lactation, and cancer mechanisms, yet these interconnected topics are often divided across different research fields. Emerging evidence also suggests a role for genomic imprinting in the regulation of postnatal resource allocation via lactation and milk composition. This review aims to provide a summary of current knowledge on genetic influences affecting milk composition, offering a holistic perspective that unifies mammary gland physiology, milk biochemistry, lactation epidemiology, and genetics.