Researchers from the University of Warsaw have discovered that breastfeeding women with smaller breasts produce milk with a higher concentration of lactose.
Lactose is a major component of breast milk, providing about 40% of the energy needed by infants, and supports the development of the central nervous system. It also helps babies absorb calcium and iron.
The study recruited 137 women, with detailed data collected on each mother and infant. The research team also measured breast size, while breast milk samples were collected and analyzed in the laboratory.
Researchers found that smaller breast size indicates higher levels of lactose in milk, compared to larger breast size.
No association was found between breast size and milk energy density, protein or fat content.
The researchers said hormonal factors may explain their findings, as larger breast size has been linked to higher levels of the hormones oestradiol and progesterone, which can reduce overall milk production and prevent lactose formation.
The team explained that this is the first study that indicates a negative relationship between the concentration of lactose in breast milk and its volume.
The study was published in the American Journal of Human Biology.