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Exercise can cut risk of breast cancer

BMJ 2003; 327 doi: (Published 18 September 2003) Cite this as: BMJ 2003;327:640
  1. Scott Gottlieb
  1. New York

    Even fairly modest levels of physical activity can decrease a woman's risk of breast cancer, a new study shows.

    Dr Anne McTiernan, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues prospectively studied data from more than 74 000 women between the ages of 50 and 79 years old who participated in the women's health initiative study from 1993 to 1998. That study was halted last summer after it found that the risks of hormone pills containing oestrogen and progestogen outweighed the benefits for post-menopausal women (JAMA 2003;290:1331-6).

    In the current study, women were asked if they usually did strenuous or very hard exercises (long enough to work up a sweat and make their heart beat fast) at least three times a week at ages 18, 35, and 50 years.

    They were then were asked how often they walked outside the home for more than 10 minutes without stopping, the usual duration and speed of such walks, and how often they exercised at strenuous levels (that increased heart rate and produced sweating).

    Examples of strenuous activities that the researchers gave the women included aerobics, aerobic dancing, jogging, tennis, and swimming laps. Women were asked similar questions about moderate and low intensity physical activities. Examples of moderate intensity activities included cycling outdoors, using an exercise machine, calisthenics, easy swimming, and popular or folk dancing. Examples of low intensity activities included slow dancing, bowling, and golf.

    The researchers found 1780 cases of newly diagnosed breast cancer over a mean follow up period of 4.7 years. Compared with the less active women, women who engaged in regular strenuous physical activity at age 35 years had a 14% lower risk of breast cancer (relative risk 0.86 (95% confidence interval 0.78 to 0.95)).

    Similar findings were seen for strenuous physical activity at ages 18 years and 50 years. Increasing physical activity was associated with a lower risk of breast cancer.

    Women who engaged in the equivalent of 1.25 to 2.5 hours a week of brisk walking had an 18% lower risk of breast cancer (relative risk 0.82 (0.68 to 0.97)) than inactive women. Women who engaged in the equivalent of 10 hours or more a week of brisk walking had a slightly greater risk reduction.

    The effect of exercise was most pronounced in women with the lowest body mass index (<24.1), but an effect was also seen in women with a higher body mass index (24.1 to 28.4).

    A separate study found that moderate exercise combined with dieting is about as effective as intense exercise in helping young women lose weight and improve their cardiovascular fitness (JAMA 2003;290:1323-30).