For women, being overweight or obese after menopause increases the risk of breast cancer.
Before menopause, your ovaries make most of your estrogen, and fat tissue makes only a small part of the total amount. After menopause (when the ovaries stop making estrogen), most of a woman’s estrogen comes from fat tissue. Having more fat tissue after menopause can raise estrogen levels and increase your chance of getting breast cancer. Also, women who are overweight tend to have higher blood insulin levels. Higher insulin levels have been linked to some cancers, including breast cancer.
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. Also, having extra fat in the waist area may raise risk more than having extra fat in the hips and thighs.
And even though gaining weight can raise your cancer 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 or to be able to study them over an extended length of time.
Evidence is growing that regular physical activity reduces breast cancer risk, especially in women past menopause. The main question is how much activity is needed. Some studies have found that even as little as a couple of hours a week might be helpful, although more seems to be better.
Exactly how physical activity might reduce breast cancer risk isn’t clear, but it may be due to its effects on body weight, inflammation, hormones, and energy balance. The American Cancer Society recommends that adults get 150 to 300 minutes of moderate intensity or 75 to 150 minutes of vigorous intensity activity each week (or a combination of these). Getting to or going over the upper limit of 300 minutes is ideal.