Talk Transcript: Mary Carmichael on Exercise and the Brain

Four times a week, Anne Rinn, 28, a psychology professor in Bowling Green, Ky., whose mother died of breast cancer, goes to kickboxing, aerobics or Pilates classes. Liz Usborne, a 64-year-old breast-cancer survivor, lobs tennis balls over the net and circuit-trains at a women's gym near her home in Bonita, Calif. The thread binding them? Concern about getting—or surviving and thriving after—breast cancer.

The American Cancer Society estimates that this year, 241,000 women will learn they have breast cancer and 40,000 women will die of it. Fortunately, a growing list of effective therapies developed during the past decade has helped extend lives, one reason that deaths from breast cancer have been dropping slowly since 1990. Living among us are more than 2 million women who have undergone breast-cancer treatments.

Modern miracle drugs like tamoxifen and raloxifene routinely cut risk for breast cancer in women whose medical histories or genes make them especially vulnerable to it. But reams of research also suggest that exercise—an activity as old as the human race—substantially reduces the odds of ever getting the disease, lengthens survival and considerably enhances quality of life for women with breast cancer.

Scientists don't completely understand why exercise is so important, but they're actively looking for answers. Roughly two thirds of all breast cancers are considered estrogen-positive; that means that the hormone estrogen fuels their growth. The rest are estrogen-negative. Many experts believe regular exercise lowers the amount of estrogen circulating through the body in the bloodstream. So for certain types of breast cancer, less estrogen equals less fuel. Exercise also pares off hormonally active fat tissue. Fat manufactures a substance called aromatase that converts hormones known as androgens to estrogen. After menopause, when the ovaries stop cranking out high levels of estrogen, this hormonal cascade becomes the major source of estrogen in a woman's body.

Recently two large, carefully designed studies suggested exercise may work through more than just hormonal mechanisms linked to estrogen. In a study published last month in the Archives of Internal Medicine, researchers speculated that exercise might affect tumor aggressiveness. The researchers found that long-term moderate or strenuous activity over a lifetime cut risk for developing estrogen-negative invasive breast cancers (though not estrogen-positive cancers). Since fewer therapies are effective against estrogen-negative cancers, that's heartening news. Some earlier research on exercise suggests it lowers risk for estrogen-positive cancers, too. Scientists are also looking beyond estrogen at the effects exercise has on insulin, leptin and certain growth factors.

Regular exercise early in life, particularly around puberty, and exercise vigorous enough to suppress other reproductive hormones may make a difference, too. A 2005 multicenter study on lifetime activity matched more than 4,000 white and black breast-cancer survivors with controls. Researchers found a 20 percent decrease in breast-cancer risk for the most versus least active women.

After a woman is diagnosed, exercise can dramatically lengthen survival and lower the odds of another tumor. For up to 14 years, the Nurses' Health Study tracked nearly 3,000 participants diagnosed with breast cancer. Researchers found that recurrence rates and deaths from breast cancer (and from all causes) dipped 26 to 40 percent among those who exercised most, compared with their sedentary peers. Brisk walking or equivalent energy-burning activity for three to five hours a week—about 30 minutes a day—netted the biggest benefits. But even being active for one to three hours a week reduced risk to some degree.

Excess pounds lower the likelihood of survival after breast cancer. But for many women, maintaining a healthy weight is often a struggle, especially during treatment. Chemotherapy or radiation can make women feel too tired to exercise. Steroids given to help ease certain side effects of chemotherapy prompt a ravenous appetite. Nausea can lead to almost continuous nibbling of comfort foods to settle queasy stomachs. Some anticancer medications that work by tampering with hormones may have a hand in weight gain, too. One such hormonal drug is tamoxifen, which keeps estrogen from entering breast cells by blocking receptors inside the cells that allow access. Studies have yet to confirm a connection, but many women on tamoxifen complain of watching the scale inch upward. No matter what the root cause is for weight gain, exercise of all sorts helps burn calories. And paradoxically, for those who feel too wiped out to fit exercise in, some evidence shows light to moderate activities may actually alleviate treatment-induced fatigue.

Doctors once believed upper-body resistance training was apt to trigger the chronic swelling and discomfort of lymphedema in women treated for breast cancer. Lymph is a thin, milky fluid that collects in spaces between cells. Carrying germ-battling immune cells, it seeps through a lacy network of channels in the body before draining into the circulatory system. Lymphedema occurs when lymph backs up, often in an arm or sometimes in the torso, after surgery or radiation alters lymph channels. Several recent studies suggest that a gradual approach and proper precautions make resistance training unlikely to raise the risk of developing Lymphedema or worsening it if it already exists.

That's important news. Resistance training helps reverse the muscle loss and fat gain called sarcopenia that often follows chemotherapy and hormonal therapy. It's helpful in other ways, too. Osteoporosis, which sets the stage for life-altering bone fractures, may be hastened by certain anticancer treatments. Chemotherapy, for example, sometimes pushes women into early menopause by prematurely shutting down their ovaries. Since estrogen helps protects bones, losing it speeds bone-thinning, particularly in the spine and hips, which are especially vulnerable to fractures. Also known to contribute to osteoporosis is a class of breast-cancer drugs called aromatase inhibitors that cut off the most plentiful supply of estrogen after menopause by interrupting the process that converts androgens into estrogen. Resistance training slows bone loss and may even strengthen bones.

Quality of life counts, too. In clinical trials, moderate to vigorous exercise programs notched up progressively to 45-minute sessions at least three times a week eased anxiety and depression, enhanced mood and self-esteem, and helped counter fatigue.

Thus far, there are few studies of exercise in women with advanced breast cancer, although early evidence suggests that physical activity offers benefits here, too, such as less fatigue. More rigorous studies investigating links between breast cancer and exercise are underway. Don't settle back to await developments, though. Rise from your reading and head out for a walk.

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