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    Physical activity's positive effect on breast cancer stems from another cause, researchers suggest

    By Robert Preidt

    HealthDay Reporter

    FRIDAY, March 11, 2016 (HealthDay News) -- Researchers report that exercise does not appear to affect breast density -- a major risk factor for breast cancer.

    Women with dense breasts are at increased risk for breast cancer, and physical activity is known to help protect against breast cancer. Previous research looking at a possible connection between exercise and breast density have been inconclusive.

    This latest study found no link between the two. This suggests that physical activity's protective effect against breast cancer is due to other factors, according to lead researcher Shadi Azam, from the University of Southern Denmark, and colleagues.

    The findings were culled from a review of the physical activity levels of more than 5,700 women in Denmark. The women were screened for breast cancer between 1991 and 2001.

    The study was presented Thursday at the European Breast Cancer Conference in Amsterdam, Holland.

    "We know that breast density is one of the strongest risk factors for breast cancer risk. Women with high density breasts -- more than 75 percent mammographic density -- have a four to six times' higher risk of developing the disease than do those women with a breast density of lower than 25 percent," Azam said in a conference news release.

    "This is because increased breast density reduces the sensitivity of mammograms and makes it far more difficult to spot small tumors. It is also because breast density per se can lead to an increased risk of most of the cellular abnormalities that lead to breast cancer," she explained.

    About 56 percent of the women in the study had mixed or dense breasts. More than 47 percent played sports, and about 70 percent cycled. Just over 50 percent of the women gardened and nearly 93 percent walked, according to the study.

    Initially, the researchers noted a link between participation in sports and cycling with the odds of having denser breasts. But, when they adjusted for other potential risk factors, the association was no longer significant, Azam said.

    The researchers also didn't find any big differences in breast density from walking or gardening, Azam added.

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