Lindsay Frazier, MD, Sc M, of Dana-Farber Cancer Institute

Many adolescent women shun red meat, driven by the lure of clothes-hanger figures and runway looks. But for those who don't, here's a reason to reconsider: Eating a lot of red meat during adolescence may increase the risk of breast cancer among premenopausal women, a new study reports.

 The findings are based on a study published in a recent issue of Cancer Epidemiology, Biomarkers and Prevention conducted by Dana-Farber oncologist Lindsay Frazier, MD, ScM, and colleagues at the Harvard School of Public Health and Harvard Medical School.

Red meat consumption during adulthood has been previously shown to spur hormone-fueled breast cancer in women ages 26 to 46. The new study is the first prospective study to show a connection between a diet high in red meat during adolescence and the development of pre-menopausal breast cancer. A prospective analysis is an investigation that follows a group of women over time instead of establishing a link through medical records of past diagnoses.

"The window of time between first menstruation and pregnancy is most likely when cells in the breast tissue are dividing in response to estrogen (the female sex hormone). Pregnancy causes breast cells to stop dividing and to differentiate terminally. This period may be when a woman is most vulnerable to environmental exposures to carcinogens, including those in the diet," Frazier says.

The researchers, including Eleni Linos, PhD, of Harvard School of Public Health, Walter Willett, MD, MPH, of Harvard Medical School, Eunyoung Cho, D Sc, of Harvard Medical School, and Graham Colditz, MD, Dr PH, of Washington University in St. Louis, Miss., examined the incidence of invasive breast cancer between 1998 and 2005 among 39,268 premenopausal nurses who had completed, in 1997, a 124-item food frequency questionnaire on their diet during high school as part of a larger epidemiological study, the Nurses' Health Study II, conducted by the National Institutes of Health. None of the women had been diagnosed with cancer before 1998.

Based on the amount of red meat consumed in adolescence and total calorie intake, the researchers divided the participants into five groups, each representing a "quintile" and corresponding to a certain average amount of red meat consumed per day.

Frazier and her colleagues found that 455 new cases of invasive breast cancer had been diagnosed between 1998 and 2005, almost 60 percent of which were stoked by estrogen. Women in the highest quintile, who had eaten two and a half red meat servings per day (or 262 grams) had a 34 percent greater likelihood of developing breast cancer than those in the lowest quintile, who had eaten less than one serving per day (or 68 grams). The risk rose by 20 percent for each additional 100 grams consumed per day. The average red meat consumption among women today hovers around 68 grams per day, Frazier says.

The kinds of red meat the women consumed included beef, pork, lamb, processed meats, bacon, hot dogs, and meatloaf. The link between breast cancer and eating any one of those kinds of meat, however, did not prove to be statistically significant.

Although the mechanism by which red meat sends cells in breast tissue cascading toward cancer is unknown, hypotheses abound. Cooking red meat at high temperatures, as is often the case for well-done or fried meats, creates cancer-causing chemicals, called heterocyclic amines, which mimic estrogen. Alternatively, red meat may be laden with hormones used to grow cattle. These hormones have been shown to cause cancer in breast tissue in laboratory experiments. Iron from red meat can produce chemical cannonballs, called free radicals, which damage DNA and lead to haywire cell division, thwarting the cell's gatekeepers to growth.

Frazier cautions that the findings were based on the participants' ability to recollect their red meat consumption, although the reported amounts were confirmed using independent tests. "Nonetheless, this study adds considerable evidence to the established adverse effects of red meat. That's clearly one of its most important messages," Frazier notes.