In the news recently was the actress Angelina Jolie, who underwent a bilateral mastectomy, not because she had breast cancer, but because her family and genetic history was such that her risk of eventually developing breast cancer was over 85%, and she wanted to essentially eliminate that risk.
Angelina had undergone a new and expensive blood test (more than USD 3000) that determined she had a mutation in one of her genes (called BRCA1) which gave her the high risk. But genes are only one of the risk factors in breast cancer, and until the price of these genetic tests falls significantly, few women will be able to have this testing done.
Fortunately however, there is something all women can do, which costs nothing, that lowers their risk of developing breast cancer; the most common cancer in women worldwide. That something is aerobic exercise, but it does not mean you have to go to the gym. Let’s look briefly at two studies that show how much exercise you need to do, and why it works.
Published last year in the journal Cancer, researchers at the University of North Carolina (USA) found that women who exercised even a small amount decreased their risk of developing breast cancer by 6%, but women who exercised more regularly—from 10 to 19 hours per week—enjoyed a 30% decreased risk.
The exercise could take the form of housework or walking as well as any time spent in the gym. The point is to be physically moving and expending energy for a couple hours every day.
The second study explains why exercise helps. It has long been known that some breast cancers are stimulated to grow by higher estrogen levels. Published in Cancer Epidemiology, Biomarkers and Prevention, investigators found that women who exercised lowered their estrogen levels, and also improved their estrogen metabolism.
After estrogen (like any hormone) performs its function, it is “broken down” or changed into what are called metabolic products before they are excreted in the urine. And, similar to what you might know about cholesterol…that there is an ideal ratio of “good” cholesterol to “bad” cholesterol… some of the metabolite products of estrogen that are considered “good”, and some not so favorable.
What the exercise did was improve this ratio. Women who exercised had a higher amount of the “good” estrogen metabolites, and less of the “bad” ones. The good ones don’t seem to cause breast cancer as much, but the bad metabolites may stimulate cancers to grow.
Medical researchers already know that excess body fat causes hormonal changes that increases the risk of other cancers too. Women who want to lower their risk of breast cancer would be smart to keep their body fat low, and to do some moderate physical activity, of any type, preferably at least 10 hours per week.
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