Fruits & vegetables. “Several studies have reported that women who consume more fruits and vegetables, especially ones that are rich in carotenoids like beta-carotene, have a reduced risk of postmenopausal breast cancer, especially for estrogen-receptor negative disease,” says Regina Ziegler, senior investigator at the National Cancer Institute.
“And any lifestyle change that reduces the risk of estrogen-negative breast cancer would be really, really good.” That’s because researchers know less about tumors that aren’t fueled by estrogen.
“Estrogen-negative breast cancer is more lethal that estrogen-positive cancer, and less is known about preventing it, so that makes this finding especially interesting,” says Walter Willett, chair of the nutrition department at the Harvard School of Public Health. “Fruits and vegetables have a pretty small impact overall on cancer, but this is one case where there may be some benefit.”
Vitamin D. Earlier evidence had suggested that women with higher blood levels of vitamin D have a lower risk of breast cancer, but the picture is muddy.
“We’re now analyzing vitamin D levels for 24,000 women from 17 cohorts around the world,” says Ziegler. “That should tell us whether the blood levels that people currently attain from sunlight, food, and supplements protect against breast cancer.”
Meanwhile, the VITAL trial is testing whether women who take 2,000 IU a day of vitamin D for several years are less likely to get breast cancer than placebo takers. “That should tell us whether high doses reduce risk,” notes Ziegler.
Soy. Over the years, the pendulum has swung between seeing soy as a food that prevents breast cancer to seeing it as one that promotes breast cancer.
“We can’t look at soy very well in our studies of U.S. women, because they don’t consume enough,” says Willett. “Data from a study in Shanghai suggest that soy consumption during adolescence and early life may reduce breast cancer risk, but there’s not much benefit later in life.”
Meat or saturated fat. Some studies have reported a higher risk of breast cancer in women who consume more saturated fat. “But the effect of saturated fat during midlife or later is weak, if it’s there at all,” says Willett.
However, a meat-heavy diet may boost risk, he argues, especially if it’s eaten in early adulthood.
“Looking at diet early in life, when we know that the breast is more susceptible, we’ve seen some increase in the risk of premenopausal breast cancer with red meat,” says Willett.
It’s not clear why. “It’s probably something in red meat other than the fat,” he says. But so far, heme iron or carcinogens that are created when meat is cooked doesn’t seem to explain the risk.
Sources: J. Natl. Cancer Inst. 105: 219, 2013; Am. J. Clin. Nutr. 89: 1920, 2009; J. Natl. Cancer Inst. 106: dju068, 2014; BMJ 2014. Doi:10.1136/bmj.g3437.