Virginia Tech study suggests breast milk composition varies with time of day and influences infant development

Virginia Tech researchers are investigating how the timing of breastfeeding impacts milk’s composition and its potential effects on infant growth, with preliminary evidence indicating circadian rhythms in milk bioactive molecules that could shape future infant nutrition practices.

Virginia Tech researchers are exploring whether the timing of breast-feeding changes what a baby receives at the breast, with early work suggesting that milk from the same mother can vary meaningfully across the day. Blakely Lockhart, a doctoral candidate at Virginia Tech’s Fralin Biomedical Research Institute at VTC, is examining whether those shifts help match an infant’s changing nutritional and metabolic needs. The project is being backed by a Pediatric Novice Research Grant from the Gerber Foundation.

According to research cited by the team, human milk is not a fixed substance but a moving target, with studies over the years finding 24-hour changes in hormones, bioactive compounds and even the milk microbiome. Earlier work has reported higher melatonin at night and shifts in cortisol and other factors across the day, while separate research has identified daily variation in microRNAs, small regulatory molecules that help control how genes are expressed. A recent review in PubMed describes breast milk as a form of “chrononutrition”, meaning food whose composition is aligned with the body’s internal clock.

Lockhart said milk chemistry can change “in a day, in a month, in a year”, and she and Brittany Howell, her adviser and an associate professor at the institute, believe those rhythms may matter for infant development. Howell said the work could help determine whether the milk’s changing composition has measurable effects on growth and body composition. Preliminary evidence from her lab suggests that signalling molecules in milk may also follow a daily pattern, potentially helping prepare infants for periods of higher energy demand.

The study will compare microRNA levels in morning and evening samples and follow infant growth during the first 6 months of life. Lockhart hopes the findings will eventually inform how pumped milk is stored and timed, as well as guide future formula design. That point matters because formula-fed children have been found to carry a higher risk of obesity later in life than breastfed infants, even when calorie intake is similar. As Lockhart put it, formula lacks many of the bioactive molecules found in human milk, “But they could be.”