Long-Term Strenuous Physical Activity Lowers Risk of Breast Cancer

NEW YORK (Reuters Health) Mar 02 - Strenuous recreational exercise over a long period of time appears to protect women against breast cancer, according to data from the prospective California Teachers Study.

There is some evidence in the published literature that physical activity can reduce breast cancer risk, Dr. Leslie Bernstein and her associates note in their paper, published in the Archives of Internal Medicine for February 26. Purported biological mechanisms include physical activity's effect on endogenous hormones, metabolism and immune function.

Dr. Bernstein, from the University of Southern California, Los Angeles, and her associates examined the relationship between recreational physical activity and breast cancer in a large cohort of women.

"This is the first cohort study to collect information on physical activity over a long period of time -- up to 40 years -- from the time these women started high school through age 54 years," Dr. Bernstein told Reuters Health.

The subjects reported their participation since high school in moderate activities - brisk walking, golf, and volley ball - and more strenuous exercise - swimming laps, calisthenics, running and jogging - as well as the amount of time participating in these activities. They also provided information regarding other known risk factors.

Included in the evaluation by Dr. Bernstein's group were 110,599 women ages 20 to 79 with no history of breast cancer at baseline in 1995. By the end of 2002, invasive breast cancer had been diagnosed in 2649, and in situ breast cancer in 593.

Analysis fully adjusted for other risk factors revealed that the risk of invasive breast cancer was reduced among subjects who participated in strenuous activity for more than 5 hours/week, versus those with no more than 30 minutes (relative risk, 0.80, p for trend = 0.02). Results were similar for in situ breast cancer risk (RR, 0.69, p for trend = 0.04).

"The study substantiates the findings that physically active women have lower breast cancer risk and it demonstrates that this applies not only to invasive breast cancer but also to in situ breast cancer," Dr. Bernstein continued. "This suggests that physical activity actually works early in the developmental process by which a cancer occurs, because it also is protective for in situ cancers.

Both strenuous (RR, 0.45) and moderate (RR, 0.53) long-term activities were associated with reduced risk of estrogen receptor-negative tumors (p for trend = 0.003 for both). However, no amount of exercise affected the risk for estrogen receptor-positive tumors.

"Exercise has many health benefits; however, from my series of studies it seems that it works best in reducing breast cancer risk if started in adolescence and maintained throughout life," Dr. Bernstein said.

"Nevertheless," she added, "I would still say it is never too late to start being physically active. With regard to breast cancer patients, the Nurses Health Study evaluation of the impact of exercise activity after diagnosis shows that active women have lower risk of recurrence and death than inactive women. Thus, it appears that exercise has benefits after a diagnosis as well."

Arch Intern Med 2007;167:408-415.

Source: http://www.medscape.com/viewarticle/553082?src=mp