2018

How environmental exposures during puberty affect lifetime breast cancer risk


Most studies have focused on older women, but breast cancer can take decades to develop, and children may be most susceptible to the effects.

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DECADES OF RESEARCH ON DIETARY, BEHAVIORAL, and other environmental risk factors for breast cancer have yielded little in the way of concrete strategies for prevention, according to Karin Michels, PhD, professor and chair of the Fielding School’s Department of Epidemiology. Michels believes that’s because the vast majority of epidemiological research into breast cancer has focused on women at late stages of adulthood. 

For the last three decades, Michels has been among a minority of breast cancer researchers studying the time between conception and puberty — specifically, how environmental influences during this time period affect later breast cancer risk. “Even though breast cancer tends to be diagnosed later in life, it usually develops over many decades, so if you’re looking at risk factors in older women, that’s probably too late,” Michels explains. “We also know that breast cells are most vulnerable during that early phase of life, and that early-onset breast cancers, in particular, are affected by early-life events.” 

Michels is the principal investigator of two multi-year National Institutes of Health grants (Environmental Chemicals And Postpubertal Breast Composition In A Latino Cohort 1U01ES026130Predictors Of Mammary Gland Development & Breast Fibroglandular Volume At Puberty R01CA158313) that use a cohort of 515 prepubertal Chilean girls to investigate the impact of a variety of factors — including exposure to endocrine-disrupting chemicals, frequent consumption of high-fat dairy products and red meat, and blood levels of certain inflammatory markers — on two early markers of breast cancer risk: the density of breast tissue and onset of breast development. Michels and others have found that higher birth weight and early onset of menarche are associated with increased breast cancer risk later in life. 

While research has shown little association between the diets of adult women and their breast cancer risk, Michels’ work suggests that diet in early life can have an impact. Most recently, in a study published earlier this year in the American Journal of Clinical Nutrition using data from the cohort of Chilean girls, Michels and colleagues found that a higher consumption of sweetened, artificially flavored milk-based drinks is associated with greater breast density, while higher yogurt intake is associated with lower breast density and delayed age at menarche (Dairy intake in relation to breast and pubertal development in Chilean girls, April 2017). 

Michels notes that the last six decades have seen a sharp increase in hormonally active synthetic chemicals introduced into the environment. “The effects of these chemicals on adults have been studied, but children, relative to their size, are exposed to much higher doses,” Michels says. “If we learn that exposure to these chemicals affects girls’ future hormonal development and breast cancer risk, that would be a wake-up call to be much more proactive in reducing the chemicals that surround us in our daily lives.” 

To ensure the impact of her group’s findings related to chemicals, diet and other factors, Michels designed an outreach component in the grant, which includes working with community-based organizations throughout the U.S. and giving public talks to disseminate the results and offer practical advice on reducing risk. “There is often a long delay before anything comes of important research findings,” Michels says. “With this grant we are immediately translating our findings into action.” 

The study Dairy intake in relation to breast and pubertal development in Chilean girls was published in the American Journal of Clinical Nutrition in April, 2017. 

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