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How Much Does Lifestyle Affect Breast Cancer Risk?

Study Suggests Weight, Drinking Habits, and Physical Activity Account for Small Portion of Overall Risk

Analyzing Cancer Risk continued...

Here's an example. The study predicts that a woman who is 65 years old with no other risk factors will have an average risk of developing breast cancer within the next 20 years of about 6.5%. If that woman stopped drinking alcohol, started exercising for at least two hours each week, and maintained a normal body weight, her absolute risk of getting breast cancer would drop about 1.6%, to 4.9%.

Here's the part that often ends up in news headlines. Exercising, staying slim, and not drinking alcohol accounted for about 24% of her overall risk of getting breast cancer. So by doing all those things, she's reducing her risk for breast cancer by 24%, which sounds like a sizeable chunk. But it's only a part of an already small number.

"The really key factors for developing breast cancer are family history and increasing age. All of the other factors are relatively weak," says Ruth O' Regan, MD, an associate professor at Emory University's Winship Cancer Institute in Atlanta.

"These modifiable factors kind of fit into those slightly weaker factors," she says. "If you're at average risk, this is sort of an encouraging paper."

Experts are quick to add that beyond breast cancer risk, there are plenty of other reasons -- heart disease and diabetes among them -- to stay slim, get regular exercise, and have a moderate alcohol intake.

And they point out that lifestyle factors do make more of an impact, however, when a woman has more things in her breast cancer risk profile that she can't change.

According to the study, a 65-year-old woman with a family history of breast cancer has a 13.8% chance of developing breast cancer within the next 20 years. If she maintains a normal body weight (BMI under 25), exercises for at least two hours each week, and stops drinking alcohol, her absolute risk drops by 3.2%, to 10.6%, or a 23% drop in relative risk.

A 65-year-old woman who has the highest numbers of non-modifiable risk factors has a 20-year absolute risk of getting breast cancer of 18.6%. By exercising, watching her weight, and not drinking alcohol, she cuts that risk by 4.1%, for a 22% decrease in her relative risk, the study found.

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