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Exercise lowers risk of breast cancer



Breast cancer can be a devastating disease, but most women can take active steps to reduce their risk, say some of the nation's leading breast cancer experts.

Women shouldn't blame themselves for their illness, doctors say, noting that it's usually impossible to pinpoint what caused an individual woman's breast tumor.

But about 25% of all breast cancer cases in women of all ages could be avoided by maintaining a healthy body weight and doing regular physical activity, says internist Anne McTiernan, a researcher with the Fred Hutchinson Cancer Research Center in Seattle. "The greatest benefits for breast cancer reduction come from weight control and physical activity together."

Alpa Patel, an American Cancer Society epidemiologist, agrees that these are "modifiable risk factors," along with limiting alcohol intake.

It may seem obvious, but being female is the main risk factor for breast cancer, the cancer society says. Men also may develop it, but the disease is about 100 times more common among women than men. This is likely because men have less of the female hormones estrogen and progesterone, which can promote breast cancer cell growth, the group says.

A woman's risk of developing breast cancer increases as she gets older. About one in eight U.S. women will develop invasive breast cancer, the cancer group says.

A large part of breast cancer risk is determined by women's lifetime exposure to estrogen, Patel says. Your risk increases if you begin your period early, if you go through menopause late, if you have fewer children or if you have them later in life. Those are considered non-modifiable risk factors, she says.

About 5% to 10% of breast cancer cases are thought to be hereditary, resulting directly from gene defects, called mutations, inherited from a parent, the cancer society says.

A small percentage of women, including actress Angelina Jolie, "have genes that put them at a very high lifetime risk," Patel says. Jolie opted for a preventative double mastectomy after learning she carried a mutation called BRCA1, which gave her an 87% chance of breast cancer.

The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 and BRCA2 genes, the cancer society says. Women with those genes need to be thinking of more intensive ways of reducing their risk, McTiernan says.

But breast cancer that isn't linked to genes appears to be connected to lifestyle and environment, she says. Her studies show that weight loss and exercising regularly combined have the most impact on improving the biomarkers, including estrogen and insulin, for breast cancer risk.

Two-thirds to three-quarters of breast cancers occur after menopause, and obesity is most clearly linked to those cases. That's partly because body fat raises levels of estrogen, which fuels most breast cancers. "If a woman is overweight or obese, she most likely is making a lot of estrogen," McTiernan says. "If a woman doesn't have lot of fat tissue, chances are her estrogen is low."

With weight loss, you don't have to go from being a heavy person to being slim, she says. "We're talking about getting off 5% to 10% of your weight, preferably 10%. So if a woman weighs 200 pounds and loses 20 pounds, it will make a huge difference in her risk for breast cancer."

Another hormone that comes into play for breast cancer is insulin. Insulin helps glucose (sugar) get into cells, where it is used for energy.

"You need insulin for life, but too much is bad for you," McTiernan says. People who are obese tend to make too much insulin. It's not made by the fat tissue, but the fat tissue causes it to increase, she says.

Heavy people tend to develop "insulin resistance, a condition where the body can't use the insulin you have, so you keep making more and more, and the excess insulin is associated with increased breast cancer risk," she says. "Weight control helps keep insulin at the right level."

Patel adds that "while not as well-established as the estrogen pathways, there is increasing evidence that insulin pathways may also be involved in breast cancer risk."

She says the verdict is still out on whether weight loss alone reduces risk, partly because many women regain the lost pounds. Researchers are currently studying how much weight loss is needed and how long women have to keep the weight off to lower their breast cancer risk, Patel says.

Photos by Scott Eklund for USA TODAY

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