Studies of blood and breast milk from mothers have demonstrated that dioxins are eliminated from the body during breast feeding. The purpose of this paper is to explore the relationship between dioxin levels in blood and breast feeding for participants in a large population-based exposure study. The focus is on exploring 1) the effects of breast feeding a first child compared to additional children and 2) a time period interaction related to the changing levels of dioxins in the environment over time.
The data come from the University of Michigan Dioxin Exposure Study (UMDES) which was conducted to identify exposure pathways by which dioxin contamination in the environment contribute to dioxin concentrations in blood. Blood samples were collected from 946 study participants in Midland, Saginaw, Bay, Jackson, and Calhoun counties in Michigan in 2004–2005. Information on pregnancy and breast feeding were obtained during an hour-long interview of each study participant. Linear regression models were run for the log10 of the blood TEQ (calculated based on the WHO 2005 TEFs), adjusting for all other covariates in the UMDES model including age, body mass index, smoking status, food consumption, and recreational activities.
532 of the study participants were women, 442 of the women had at least one child, and 240 of the women with at least one child breast fed for at least one month. After adjusting for covariates, breast feeding a first child and additional children were both significantly associated with a lower TEQ in blood. The effect of breast feeding a first child was larger than the effect of breast feeding additional children. The parameter estimates indicate that each six month increase in breast feeding a first child was associated with a 7.6% decrease in blood TEQ and each six month increase in breast feeding additional children was associated with a 2.3% decrease in blood TEQ.
In general, breast feeding before 1959 was significantly associated with a higher TEQ in blood while breast feeding from 1960–1979 and after 1980 were significantly associated with a lower TEQ in blood. This suggests that breast feeding during the historic period when the dioxin content in the food supply was high was not associated with reductions in blood TEQ, whereas breast feeding more recently when the women were eating less contaminated foods was associated with reductions in blood TEQ.