A healthy diet may trim breast cancer risk

Organic vegetables are shown at a Whole Foods Market in LaJolla, California in this May 13, 2008 file photo.

NEW YORK (Reuters Health) - A woman may not be able to change her family history of breast cancer, but she can typically control what she eats and drinks. And consuming more vegetables and whole grains -- and less alcohol -- just might trim her chances of getting the disease, according to an analysis of published studies.

"As the incidence of breast cancer continues to rise, with many of the risk factors for the disease non-modifiable, potentially modifiable risk factors such as diet are of interest," Dr. Sarah Brennan of Queen's University Belfast in Northern Ireland, who led the analysis, noted in an email to Reuters Health.

It's estimated that more than 120 out of every 100,000 American women are diagnosed with breast cancer each year, yielding a lifetime risk of about 1 in 8. The idea that diet might influence these numbers is not new; yet solid evidence for such a link has remained elusive.

"Even though we have hypothesized a relationship between diet and the risk of breast cancer, showing it has been very hard to do," Dr. Michelle Holmes, an epidemiologist at Harvard Medical School in Boston who was not involved in the study, told Reuters Health. Individual studies are often too small to uncover modest relationships; combining them, however, offers a better chance of detecting a diet's true effects.

After carefully reviewing the relevant research to date, Brennan and her colleagues pooled the results of 18 studies that enrolled a total of more than 400,000 people. Each study aimed to associate breast cancer risks with at least one common dietary pattern: the "unhealthy" Western diet (high in red meats and refined grains), a more prudent "healthy" diet (high in fruits, vegetables and whole grains), or varying levels of alcohol drinking.

Since foods and beverages are never consumed in isolation, this more holistic view of intake better reflects a person's diet than looking at particular nutrients, Brennan and her colleagues explain in the American Journal of Clinical Nutrition.

The team found an 11 percent lower risk of breast cancer among women in the highest versus lowest categories of the prudent diet, while those consuming larger amounts of wine, beer and spirits had a 21 percent increased risk -- a relationship that has been highlighted in many previous studies. Surprisingly, no overall risk difference was seen between high and low categories of the Western diet.

Just how a healthy diet might lower breast cancer risk is not well understood. Alcohol's link, on the other hand, is generally known: Estrogen levels are higher in postmenopausal women who drink alcohol, noted Holmes. And a higher lifetime exposure to estrogen has been tentatively linked to the disease.

Brennan stressed that these findings need to be interpreted cautiously, noting that there are inherent statistical problems in combining the results of multiple studies, in addition to the limitations of each included study, such as recall bias. She pointed to the need for more carefully designed studies in the future to further examine the diet-breast cancer link.

In the meantime, Holmes said: "Consuming a prudent, healthy diet that includes lots of fruits, vegetables and whole grains is a wise idea, because there is lots of scientific evidence that it prevents heart disease and diabetes. This study shows that an additional benefit might be a small decrease in breast cancer risk."

SOURCE: American Journal of Clinical Nutrition, March 10, 2010