Breast Cancer Survival May Be Improved by Exercise
Women who are physically active in the year before they receive a diagnosis of breast cancer are more likely to survive the disease, according to a study reported in the journal Cancer.
"We found a beneficial effect on survival for exercise undertaken in the year before diagnosis, particularly among women who were overweight or obese near the time they were diagnosed with breast cancer," says study author Page Abrahamson, Ph.D., at the Fred Hutchinson Cancer Research Center in Seattle.
In the study, Dr. Abrahamson's team analyzed data on nearly 1,300 women ages 20 to 54 who were diagnosed with invasive breast cancer between 1990 and 1992.
The researchers asked the study participants about their average frequency of moderate and vigorous physical activity when they were ages 13, 20, and during the year before their diagnosis.
An abundance of regular exercise before diagnosis was associated with improved disease outcomes.
The association was particularly strong for women with a body mass index (BMI) of more than 25 - the statistical threshold for overweight - who also reported the highest levels of physical activity in the one year before their diagnosis. (For reference, a woman 5 feet 5 inches tall who weighs 150 pounds has a BMI of 25.)
Overall, women rated in the highest 25 percent, in terms of their level of activity, were 21 percent more likely to survive than those rated in the bottom quarter.
The benefits for women with BMIs above 25 who had high levels of activity rose; they were 30 percent less likely to die than those with BMIs above 25 who engaged in low levels of activity.
Activity in the teen years or early adulthood did not have an impact on survival, according to the researchers.
"We were not able to evaluate detailed, long-term exercise," notes Dr. Abrahamson. "However, exercise levels in the year before diagnosis is likely an indicator of a person's average adult exercise patterns."
While many other researchers have suggested that exercising regularly reduces the risk of getting breast and other cancers, less is known about what effect activity has on a woman's prognosis if and when she gets breast cancer.
One previous study found a beneficial effect of exercise for both ideal-weight women and overweight women diagnosed with breast cancer, explains Dr. Abrahamson.
Exactly why this study did not show much benefit for normal-weight women is not known, she says.
"This is difficult to explain,” she says. “It is possible that our finding is a fluke and that improved survival would apply to all women with breast cancer."
Another theory revolves around weight-linked differences in circulating estrogen.
Exercise is known to lower estrogen levels, Dr. Abrahamson says.
"Once women receive radiation or chemotherapy after diagnosis, they no longer produce hormones from their ovaries,” she explains. “Therefore, lower-weight women wouldn't necessarily gain extra benefit from exercise.”
"However, for overweight women, they are still getting hormones from their excess fat tissue and are at a higher risk of dying,” she says.
“It is possible that overweight women who are exercising are lowering their hormone levels through exercise and increasing their odds of surviving, explains Dr. Abrahamson. "Previous studies have shown exercise to significantly decrease estrogen levels in overweight women."
An expert at the American Cancer Society, Alpa Patel, Ph.D., says this study adds another piece to the puzzle.
Dr. Patel, director of the Cancer Prevention Study-3, remarks that, "We know that lifelong physical activity reduces the risk of breast cancer, and some studies show even initiating the exercise in adulthood [reduces risk]."
Now, she adds, this study shows that physical activity before a diagnosis of breast cancer may help women survive.
Another expert said the study does have its flaws.
Leslie Bernstein, Ph.D., at the University of Southern California's Keck School of Medicine, says "the study suffers from the problem that the activity refers to only activity prior to diagnosis of breast cancer," rather than lifetime activity.
"When we looked at this same issue in a similar design, but with measures of activity across the lifespan up to the date of diagnosis, we saw no impact of exercise activity on the risk of dying or overall mortality."
Still, Dr. Bernstein says exercise certainly cannot hurt, and may help.
"I would recommend that women with breast cancer begin to participate in an exercise program, one that is carefully considered by their physicians, considering any [other diseases] they might have," she says.
Always consult your physician for more information.
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According to the National Cancer Institute (NCI), in 2001, experts concluded that obesity and physical inactivity may account for 25 to 30 percent of several major cancers - colon, breast (postmenopausal), endometrial, kidney, and cancer of the esophagus.
Preventing weight gain can reduce the risk of many cancers, states the NCI. Information provided by this leading federal agency shows that experts recommend that people establish habits of healthy eating and physical activity early in life to prevent overweight and obesity.
Those who are already overweight or obese are advised to avoid additional weight gain, and to lose weight through a low-calorie diet and exercise. Even a weight loss of only 5 percent to 10 percent of total weight can provide health benefits.
In 2002, about 41,000 new cases of cancer in the US were estimated to be due to obesity, according to the NCI. This means that about 3.2 percent of all new cancers are linked to obesity.
A recent report estimated that, in the US, 14 percent of deaths from cancer in men and 20 percent of deaths in women were due to overweight and obesity.
The effect of obesity on breast cancer risk depends on a woman’s menopausal status.
Before menopause, obese women have a lower risk of developing breast cancer than do women of a healthy weight. However, after menopause, obese women have 1.5 times the risk of women of a healthy weight.
The NCI states that obese women are also at increased risk of dying from breast cancer after menopause compared with lean women.
Scientists estimate that about 11,000 to 18,000 deaths per year from breast cancer in US women over age 50 might be avoided if women could maintain a BMI under 25 throughout their adult lives.
Obesity seems to increase the risk of breast cancer only among postmenopausal women who do not use menopausal hormones.
Among women who use menopausal hormones, there is no significant difference in breast cancer risk between obese women and women of a healthy weight.
Both the increased risk of developing breast cancer and dying from it after menopause are believed to be due to increased levels of estrogen in obese women.
Before menopause, the ovaries are the primary source of estrogen. However, estrogen is also produced in fat tissue and, after menopause, when the ovaries stop producing hormones, fat tissue becomes the most important estrogen source.
Estrogen levels in postmenopausal women are 50 to 100 percent higher among heavy versus lean women.
Estrogen-sensitive tissues are therefore exposed to more estrogen stimulation in heavy women, leading to a more rapid growth of estrogen-responsive breast tumors.
Another factor related to the higher breast cancer death rates in obese women is that breast cancer is more likely to be detected at a later stage in obese women than in lean women, according to NCI experts. This is because the detection of a breast tumor is more difficult in obese versus lean women.
Weight gain during adulthood has been found to be the most consistent and strongest predictor of breast cancer risk in studies in which it has been examined.
The distribution of body fat may also affect breast cancer risk. Women with a large amount of abdominal fat have a greater breast cancer risk than those whose fat is distributed over the hips, buttocks, and lower extremities.
Results from studies on the effect of abdominal fat are much less consistent than studies on weight gain or BMI.
Always consult your physician for more information.
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