Dropping a Few Pounds Could Lower Breast Cancer Risk

Overweight and obese women are at higher risk of developing breast cancer, but losing as little as 5% of body weight can help reduce those odds.

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Dropping just a few pounds could significantly lower women’s breast cancer risk, according to a new study. Researchers at the Fred Hutchinson Cancer Research Center in Seattle found that women who dieted and exercised to lose a moderate amount of weight also saw a drop in their levels of estrogen and other hormones associated with increased risk of breast cancer.

Previous research has shown that overweight and obese women are at greater risk for breast cancer; that’s because fat tissue boosts the production of estrogen, which in turn fuels many breast tumors. The current study is the first to show that losing weight helps reduce that risk.

The study involved 439 overweight or obese postmenopausal women ages 50-75 who were sedentary and not using hormone-replacement therapy. “We know that after menopause, women make estrogens in their fat tissue, and overweight or obese women have high blood levels of estrogens after menopause,” says lead researcher Dr. Anne McTiernan, director of the Hutchinson center’s Prevention Center. “We wanted to test whether losing a moderate amount of weight, an achievable goal for most women, could reduce their blood levels of estrogens.”

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The participants were divided into four groups: one group dieted, reducing both fat and calories, especially by cutting out sugary beverages and desserts and upping their intake of vegetables, fruits and fiber. Another group did intensive exercise: five 45-minute aerobics classes per week. A third group both dieted and exercised, by engaging in brisk walking. The fourth group did not change their diet or exercise habits.

By the end of the year-long study, women in the diet-only and diet-plus-exercise groups met the goal of the weight-loss intervention, having dropped an average of 10% of their starting weight. They also saw significant reductions in their levels of estrogen and other hormones. But even those participants who lost less weight — just 5% of their starting weight — lowered their hormone levels enough to affect their breast cancer risk. The study’s authors estimate that a 5% weight loss may lower women’s breast cancer risk by 22%.

Women in the exercise-only and control groups didn’t lose weight overall nor did they lower their hormone levels. “Exercise didn’t produce much weight loss — it never does reduce weight much without reducing calories — so we think the production of estrogens in their fat cells didn’t change,” says McTiernan.

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The study looked at three forms of estrogen — estrone, estradiol and free estradiol — along with two types of testosterone, including total testosterone and free testosterone. Researchers also measured androstenedione, a steroid necessary for sex hormone production. At high levels, all are associated with breast cancer risk, and all are higher in overweight or obese women.

The researchers also looked at sex-hormone binding globulin (SHBG), which binds to estrogen and testosterone and takes them out of circulation, in turn lowering breast cancer risk. Here’s how hormone levels were affected by the diet and exercise:

  • Estrone levels fell 9.6% with diet, and 11.1% with diet plus exercise
  • Estradiol levels dropped 16.2% with diet, and 20.3% with diet plus exercise
  • Free-estradiol levels decreased 21.4% with diet, and 26% with diet plus exercise
  • Free-testosterone levels declined 10% with diet, and 15.6% with diet plus exercise
  • SHBG levels increased 22.4% with diet, and 25.8% with diet plus exercise

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The main message of the study? It’s never too late to reap the benefits of weight loss. “Of course it’s best to make lifestyle changes earlier in life so you can avoid the weight gain that most American women are experiencing over time,” says Dr. McTiernan. “But if you’ve gained weight and find yourself overweight in your postmenopausal years, it’s not too late to make lifestyle changes to reduce calories and increase physical activity, and thereby reduce your risk factors for breast cancer.”

The authors note the findings could also apply to overweight women who are being treated with breast cancer drugs that block estrogen or stop its production, such as tamoxifen, raloxifene and exemestane. These drugs are not recommended for use longer than five years and can have side effects in some women. “Weight loss in overweight or obese women therefore represents an additional option for long-term breast cancer risk reduction,” the authors write.

The study was published in the American Society of Clinical Oncology’s Journal of Clinical Oncology.

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