Breast milk and lipid intake distributions for assessing cumulative exposure and risk.

Breast milk consumption is the primary route of infant exposure to certain lipophilic toxicants that have accumulated over decades in maternal adipose tissue, as well as to less persistent toxicants from maternal exposure during lactation. Such infant exposures occur at a time of rapid growth and development when susceptibility to certain toxicants can be greatest. Breast milk and lipid intake rates are presented for the 0-6 and 0-12 month age periods for infants fed according to the American Academy of Pediatrics' current recommendations (exclusive breast-feeding for 0-6 months and continued breast-feeding to 12 months). Intake rates are normalized to infant bodyweight to account for the covariance of consumption and bodyweight. Frequency distributions describe the population variability in intake. For age 0-12 months, daily average milk intake is 100.7 +/- 22.7 g/kg day (mean +/- SD), with a 95th percentile of 153.5 g/kg day. Breast milk intake distributions are also developed for infants exclusively breast-fed (no significant calories from non-breast milk sources) over their first year, and for the entire (nursing and non-nursing) infant population. For short-term exposures, intake can be derived from the regression equation presented here. Lipid intake estimated assuming a 4% lipid content (current risk assessment practice) is compared and found comparable to that derived from measured lipid content. The national trend of increased breast-feeding found in surveys further supports including the breast milk pathway in risk assessment.