Maintaining a healthy body weight can help women drop breast cancer risk

Excess pounds may be more dangerous to post-menopausal women than previously thought.

Too much body fat increases the chances of developing 13 types of cancer in men and women, including breast cancer in post-menopausal women, according to the Centers for Disease Control and Prevention.

A recent Spanish study concludes earlier research may have underestimated by a factor of two the number of cases of hormone-positive breast cancer in post-menopausal women attributable to obesity. According to an Oct. 17, 2024, article published in the Journal of Epidemiology and Community Health, obesity may be responsible for 42 percent of hormone-positive cases, and 38 percent of all breast cancer cases in post-menopausal women.

Earlier research estimated 20 percent of hormone-positive breast cancer and 10 percent of all breast cancer in post-menopausal women were associated with obesity, according to the Spanish paper. That earlier work used BMI (body mass index) to measure body fat. The BMI formula calculates whether a person is overweight or obese using only weight and height. The Spanish study utilized another method of measuring body weight, CUN-BAE (Clínica Universidad de Navarra-Body Adiposity index), which incorporates age and sex.

“It’s a good study,” said breast surgeon Naomi J. Kalliath, DO, at Cape Cod Healthcare Breast Surgery - Hyannis and Cape Cod Healthcare Breast Surgery - Falmouth. Hormone-positive breast cancer, in which estrogen, the female sex hormone, stimulates tumor growth, is the most common form of breast cancer, she said.

“By definition, post-menopausal women have less estrogen,” Dr. Kalliath said.

That might seem to put them at lower risk, but not for those who are obese, she said. Fat cells also produce estrogen, and large amounts of fat increase the amount of estrogen, growth hormones and inflammation in the body, raising the chances of developing breast cancer.

More About BMI and the Spanish Study

The researchers looked at data from post-menopausal women in Spain: 1,033 breast cancer cases and 1,143 control cases. They concluded BMI underestimates obesity in post-menopausal women because it doesn’t consider such factors as race, age and sex.

“It’s well known that BMI is not a good way” to measure body fat, Dr. Kalliath said.

At its annual meeting in June 2023, the American Medical Association said BMI is imperfect and should not be the sole method used to determine a person’s body fat. The AMA said disease, lifestyle and ethnicity can all affect interpretation of BMI, and combining BMI with waist circumference may be a more accurate method for adult patients.

The study’s findings were drawn from white women in Spain, so may not be directly attributable to all other populations, Dr. Kalliath said, but the findings align with research on excess weight and hormone-positive breast cancer.

She cited a January 11, 2022, article in the American Journal of Epidemiology that drew data from 31,028 women in the Black Women’s Health Study. The article said obesity was estimated to be responsible for 12-15.4 percent of all breast cancer cases in non-Black women and 28.3 percent in Black women, noting that obesity affects more Black women (56.9 percent) than non-Hispanic white women (39.8 percent). The researchers found an elevated risk of hormone-positive breast cancer, but not hormone-negative breast cancer, in post-menopausal women with high BMI. The study also looked at women’s BMI over time.

“The meta-analysis shows an increase in post-menopausal breast cancer risk by 7 percent for every 11 pounds gained after age 18,” Dr. Kalliath said.

“Black American and white cases are now about equal in breast cancer,” said Peter Hopewood, MD, FACS, a Falmouth surgeon who operates on breast and other cancers. “Black American women usually have a more aggressive breast cancer that doesn’t respond” as well to treatment.

What Can Women Do to Lower Risk?

Dr. Hopewood said several factors increase a woman’s risk of breast cancer, including:

• Having a parent or sibling with breast cancer.
• Never having been pregnant or given birth.
• A long span of time between first period and menopause.

While you can’t do anything about those factors, you can eat a healthy diet, exercise and limit or avoid alcohol, he said.

Obesity is not only fueling breast cancer cases, but “an explosion in uterine, endometrial and colorectal cancer,” Dr. Hopewood said. The Great Depression and World War II restricted the amount and variety of food available to most Americans, he continued. In the post-war years, Americans began consuming more food, a trend that continued even while more people exercise less and lead sedentary lives, leading to a rise in obesity and obesity-related diseases, including breast and other cancers.

Exercise is an extremely important way to prevent breast cancer, both Dr. Hopewood and Dr. Kalliath said.

If you exercise for 20-30 minutes five times a week, you can decrease your risk of breast cancer by 30-35 percent, Dr. Kalliath said. “Calorie counting can help,” as can skipping highly-processed foods high in sugar and fat, she added.

Women should try to avoid obesity before menopause, as it gets harder to lose weight as you age, both doctors agreed.

“You can’t work off as much,” Dr. Hopewood said.

Some breast cancer drugs, including tamoxifen, can increase this difficulty, making weight loss even harder for post-surgical cancer patients who wish to avoiding recurrence, Dr. Kalliath added.

“There are a lot of things you can’t control. It’s nice to know you can limit your breast cancer risk by a healthy lifestyle,” she said.