Advancing Our Knowledge of Human Milk and Lactation

Each August, we recognize National Breastfeeding Month. While families weigh many factors when deciding whether to breastfeed, the health benefits of human milk consumption are clear. Breast milk provides essential nutrients that infants need for optimal growth, health, and development. It also offers protection against common childhood infections and promotes better survival during a baby’s first year. 

Human milk is an enormously complex and personalized food, containing hundreds of components that vary across lactating people and change over time according to the baby’s needs. Strengthening our understanding of human milk biology and lactation is essential to support breastfeeding and to ensure the health of infants who do not have access to a lactating parent’s milk. One of NICHD’s aspirational goals is to optimize infant survival by synthesizing human milk, capturing all its components and properties, and individualizing it to the characteristics of the infant’s mother.

The NICHD-led Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) project is exploring human milk as an active biological system and working to understand the inputs of the lactating parent, the infant, and the environment. A recent supplement in the American Journal of Clinical Nutrition lays out an agenda to inform future research by studying factors influencing the synthesis, composition, and best use of human milk.

The American Academy of Pediatrics recommends exclusive breastfeeding for the first 6 months of a baby’s life, yet parents face many barriers to breastfeeding. One such barrier is perceived risk to the baby from passage of prescription drugs taken by the lactating parent into breast milk. NIH’s LactMed database summarizes known information about drugs and other chemicals to which lactating people may be exposed, but the extent of transfer of most of these substances into breast milk is unknown or based on small studies. A 2019 analysis concluded that only 2% of products in the LactMed database had recommendations based on strong data. Too often, this lack of information leads to parents either stopping breastfeeding or discontinuing needed medications. 

To bolster the scientific evidence base, we must enhance efforts to include pregnant and lactating people in research. In 2016, the 21st Century Cures Act established the Task Force on Research Specific to Pregnant Women and Lactating Women (PRGLAC). PRGLAC subsequently made recommendations to promote inclusion of pregnant and lactating people in clinical trials and issued an implementation plan. But as the COVID-19 pandemic made clear, there remains much work to be done to put these recommendations into practice. Pregnant people were excluded from participating in early clinical trials of COVID-19 vaccines and had to make decisions about vaccination in the absence of robust scientific evidence.

Thoughtfully including pregnant and lactating people in research is essential to developing clinical care recommendations based on solid evidence. The Consolidated Appropriations Act of 2023 stipulates the creation of an advisory committee to monitor and report on the implementation of the PRGLAC recommendations. NICHD will be leading this committee, which is currently being formed. NICHD has also issued a Request for Information to solicit nominations for research needs to be considered in the development of a Priority List of Drug, Vaccine, and Dietary Supplement Research Needs for Pregnant, Postpartum, and Lactating Persons. Submissions are due next month. We also are engaging with the National Academies of Sciences, Engineering, and Medicine (NASEM), which is coordinating a consensus study to develop a framework to address legal, ethical, regulatory, and policy issues for research specific to pregnant and lactating persons . A recently published brief from one of the NASEM committee’s workshops discusses liability considerations surrounding research on pregnant and lactating people and potential mitigation strategies.

Finally, NICHD supports a broad range of clinical research focused on pregnant and lactating populations. One example is the Commonly Used Drugs During Lactation and infant Exposure (CUDDLE) study conducted by NICHD’s Pediatric Trials Network. The CUDDLE study, which began enrollment in 2018, tracks how different drugs are passed through breast milk to determine dosing levels that are safe for both parent and infant. Researchers are looking at a range of drugs taken short- or long-term as part of a lactating person’s routine medical care. Findings from this study and other research focused on lactating people promise to provide the scientific evidence needed for new parents and their healthcare providers to make informed choices.