Human breast milk (HM) contains extracellular vesicles (EVs) enriched with microRNAs (miRNAs) that regulate immune, metabolic, and developmental processes in infants. Although maternal physical activity benefits infant outcomes, its influence on HM EV miRNA composition is unclear. This study examined associations between moderate-to-vigorous physical activity (MVPA; ≥3.0 metabolic equivalents) and prolonged sedentary behavior (total sitting/lying minutes of bouts ≥60 minutes) with EV miRNA expression in HM collected early postpartum. Maternal activity was measured using a thigh-worn activPAL monitor across pregnancy trimesters and days 10–18 postpartum. EVs were isolated and small RNA sequencing identified 691 unique miRNAs. Principal component analysis showed EV miRNA profiles were most strongly associated with sedentary behavior during the first two trimesters. In trimester one, prolonged sedentary behavior correlated with global EV miRNA patterns, independent of MVPA. Differential expression analysis revealed nine miRNAs linked to sedentary behavior in trimester two and two in trimesters one and three. Pathway enrichment highlighted neural development, synaptic function, RNA processing, cardiovascular and muscle development, and growth signaling. These findings suggest maternal behavior during pregnancy modulates HM EV miRNA composition, with potential implications for early-life programming. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Elliott et al. (Fri,) studied this question.
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