How Your Weight Affects Your Risk of Breast Cancer

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Managing weight is a challenge for most people in the US. In fact, according to the Centers for Disease Control and Prevention (CDC), about 69% of American adults are overweight.

This puts them at higher risk for serious conditions including diabetes, heart disease, and some types of cancer. For women, being overweight or obese after menopause increases the risk of breast cancer.

The female hormone estrogen can help breast cancer grow. After menopause, most of your estrogen comes from fat tissue. Having more fat tissue can increase your chance of getting breast cancer by raising estrogen levels. Also, women who are overweight tend to have higher levels of insulin, another hormone. Higher insulin levels have also been linked to some cancers, including breast cancer.

But the connection between weight and breast cancer risk is complicated. Studies suggest the risk appears to be increased for women who gained weight as an adult but may not be increased among those who have been overweight since childhood. For example, the American Cancer Society Cancer Prevention Study-II found that women who gained 60 or more pounds after age 18 had double the risk of being diagnosed with post-menopausal breast cancer compared to women who maintained their weight over the same time period.

And even though it’s been established that gaining weight raises your risk, it’s not clear whether losing weight reduces your risk. This turns out to be a tough question for scientists to answer, mainly because very few people actually lose weight during adulthood, and those who do lose weight don't usually keep it off over a long period of time. So it is difficult to find a large enough group of people to study.

But there is some evidence to show that losing weight helps. Research from the Nurses' Health Study found women who lost weight and kept it off for 4 or more years after menopause had a 40% lower risk of breast cancer. Another study found that weight-loss surgery was associated with an 83% lower risk of breast cancer. However, it is not clear the results from surgery patients can be applied to people who lose weight more gradually, from exercise and eating healthier.

We do know that avoiding weight gain is helpful, whether you are overweight now or not. If you’re carrying extra pounds, losing as little as 5%-10% of your weight improves your overall health. A good goal for most overweight women is to drop half a pound per week for 6 months. What's more, exercise can also lower breast cancer risk above and beyond the impact it can have on losing weight. Many studies have found that exercise is a breast-healthy habit. As little as 75 to 150 minutes of brisk walking each week has been shown to lower risk. Ramping up your exercise routine even more may lower your breast cancer risk even further.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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