Researcher Anne McTiernan, MD, PhD, is director of cancer prevention at the Fred Hutchinson Cancer Research Center and professor of medicine and public health at the University of Washington, Seattle. She's also the author of Breast Fitness: An Optimal Exercise and Health Plan for Reducing Your Risk of Breast Cancer.
"Postmenopausal women who have higher levels of estrogen and testosterone have a higher risk of breast cancer," McTiernan tells WebMD. "In our study, women who were the heaviest for their height and the least active had the highest levels of various kinds of estrogens and testosterone. Such women can have a four to six times increased risk of breast cancer compared to women at the lowest sex-hormone levels."
The findings appear in the September issue of the Obesity, the journal of the North American Association for the Study of Obesity.
Overweight + Sedentary = More Hormones = Breast Cancer
McTiernan and colleagues studied 267 postmenopausal, cancer-free women who ate high-fat diets. None of the women received hormone therapy. All of the women filled out extensive dietary and lifestyle questionnaires and had their hormone levels measured.
Women with the highest BMI (body mass index, a measure of weight in relation to height) had higher estrogen and testosterone levels than did women with a low BMI. Inactive women had higher levels of these hormones than women who exercised every day.
But the women with the highest BMI and lowest activity levels had higher hormone levels than women with just one of these factors. These women, McTiernan says, have a very high risk of breast cancer. Fortunately, there's a lot they can do about it.
"We recommend at least a half hour a day of exercise, at least five days a week," McTiernan says. "But in those who need weight control, it's much better to exercise for an hour a day, six days a week. It can be split up over the course of the day. And a woman doesn't have to become athletic -- she can just get up and walk two or three times a day."
Preventing Breast Cancer With Exercise and Diet
What about diet? Of course it's important, says dietitian Kathryn A. Allen, RD, LD, manager of the nutrition department at Moffitt Cancer Center in Tampa, Fla.
"We recommend the same thing for postmenopausal women as we do for others: a high-fiber diet with lots of fruits and vegetables, low-fat dairy products for calcium, no fried foods if at all possible, and more protein from plants and less from animals -- no more than 4 ounces per day of meat," Allen tells WebMD.
But Allen says McTiernan is right on track when she stresses exercise.
"The bottom line is that weight lossweight loss isn't enough. You may lose weight, but you'll maintain the same percentage of body fat," Allen says. "Exercise reduces fat and increases lean body mass, and thus works with weight loss to reduce breast cancer risk."
McTiernan, who is 53, takes her own advice.
"I do quite a bit: an hour and a half to two hours a day of different types of exercise," she says. "I take walks on the weekend, but also during the week I use a treadmill or elliptical trainer and also do weight training."