Exercise Reduces Risk of Breast Cancer in Black Women and White Women
According to a study published in the Journal of the National Cancer Institute, women with the highest levels of physical activity had a roughly 20% decreased risk of breast cancer. The reduction in breast cancer risk was observed in both white women and black women.
Several studies have reported that women who engage in regular physical activity are less likely to develop breast cancer than women who are inactive. It remains uncertain, however, whether the extent of this benefit varies by factors such as age, race, and family history of breast cancer. Only one previous study of exercise and breast cancer focused specifically on black women.
To assess the relationship between physical activity and risk of breast cancer, as well as to determine whether this relationship varies by race or family history of breast cancer, researchers evaluated 4538 women with breast cancer (1605 black and 2933 white) and 4649 women without breast cancer (1646 black and 3033 white).
Study participants were between the ages of 35 and 64 years of age, and were enrolled in five locations: Atlanta, Detroit, Los Angeles, Philadelphia, and Seattle. Information about lifetime physical activity was collected by in-person interviews; the focus was on activities in which the woman had participated for at least 1-2 hours per week for at least four months.
Roughly a quarter of study participants (25% of women with breast cancer and 23% of the women without breast cancer) reported no exercise between the age of 10 and the present. Black women were more likely to report being inactive than white women-roughly 33% of black women reported being inactive, compared to 18-20% of white women. Among women who did report exercise, the most common activities were walking (54% of subjects), aerobics (27% of subjects), and bicycling (21-22% of subjects).
Women who had a lifetime average of at least 1.3 hours per week of exercise had a roughly 20% reduction in risk of breast cancer compared to women who were inactive. The benefit of exercise did not vary by race (the benefit was similar for both white women and black women), nor did it vary by age, parity, body mass index, menopausal status, use of postmenopausal hormones, use of oral contraceptives, estrogen receptor status, or cancer stage. Family history of breast cancer, however, did modify the relationship between exercise and breast cancer: Among women with a first-degree family history of breast cancer, increasing levels of exercise did not decrease the risk of breast cancer.
These results provide additional evidence that for many women, regular exercise throughout life reduces the risk of breast cancer. This is one of the few studies of exercise and breast cancer that specifically evaluated black women.
Reference: Bernstein L, Patel AV, Ursin G et al. Lifetime Recreational Exercise Activity and Breast Cancer Risk Among Black Women and White Women. Journal of the National Cancer Institute. 2005;97:1671-9.
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