Although the evidence that regular exercise lowers colon cancer risk is firm, data indicating physical activities reduce breast cancer risk was regarded as unclear, in the Harvard Report on Cancer Prevention, published in November 1996. Now we have an impressively large study that strongly supports the value of physical activities in leisure and work time, to provide significant reduction in breast cancer risk.
The study involved more than 25,000 women, followed for nearly 14 years by Inge Thune, M.D., and colleagues at the University of Tromso in Norway. There were 351 cases of breast cancer during this period, and when the characteristics of these women and the cancer-free women were compared at the end of the follow-up, researchers came to these conclusions:
There was a 37% reduction in breast cancer risk among women who exercised regularly.
Biggest risk reduction occurred in lean women, women under 45 years old, and women who exercised regularly for three to five years.
Risk was also reduced by higher levels of physical activity at work, and younger women benefited the most.
While there is not a definite mechanism to explain these data, researchers believe an explanation is connected with the effect of physical activities on sex hormone concentrations and energy balance (calories in versus calories out).
Although there is a strong family history link in breast cancer (at least for susceptibility), breast cancer is one of numerous cancers that shows a strong link to lifestyle factors. The women who exercised in the study tended to have more education, higher income, smoked less, drank less alcohol, ate fewer calories, and ate less fat. All these factors may influence the incidence of breast cancer.
We cannot stress too strongly the importance of the Race for the Cure campaign. This new study underlines the value of this effort.
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