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Physical Activity Alters Diabetes Link to Breast Cancer 

Jul 29, 2008

In a case-control study among Hispanic women, physically active breast cancer survivors were 60% less likely to have diabetes compared with a physically inactive control group, Maureen Sanderson, Ph.D., of the University of Texas-Houston School of Public Health at Brownsville, reported at the Department of Defense Era of Hope meeting.

In contrast to previous studies, however, diabetes was not associated with breast cancer among physically inactive women. In fact, the breast cancer patients had a slightly lower prevalence of diabetes compared with the control group.
"The negative association between diabetes and breast cancer was unexpected, since a recent meta-analysis reported a significant positive association," said Dr. Sanderson. "Potential mechanisms that warrant exploration are related to hormone levels and the severity and treatment of diabetes."

Several studies have shown that diabetes increases the risk of breast cancer, whereas the data suggested that physical activity reduces breast cancer risk. Hispanic women, in contrast to white women, have lower rates of breast cancer and physical activity but a higher prevalence of diabetes.

Dr. Sanderson and colleagues undertook a study to evaluate potential interactions among diabetes, physical activity, and breast cancer. They also wanted to determine whether physical activity modified the effect of diabetes on breast cancer risk in Hispanic women.

Investigators interviewed 176 Hispanic women diagnosed with breast cancer from 2004 to 2008. The patients were compared with 464 Hispanic women who had a mammography at the center where the patients’ breast cancer was diagnosed.

Diabetes status (including overt and borderline diabetes) and leisure-time physical activity were self-reported. Patients and controls were grouped according to level of physical activity.

Consistent with previous studies, physical activity was associated with a decreased risk of breast cancer. Dr. Sanderson said 61.4% of the breast cancer patients reported no leisure-time activity, whereas patients reporting the most physical activity accounted for 13.1% of the group (OR 0.6, 95% CI 0.3 to 0.9). In the control group, 48% of the women reported no physical activity, and 17% fell into the highest category of physical activity.

Unexpectedly, the researchers said, there was a lower prevalence of diabetes among the breast cancer survivors than in the control group, although the difference was not statistically significant (27.4% versus 33%, OR 0.7, 95% CI 0.5 to 1.1).
Moreover, physical activity had a mixed influence on diabetes’ association with breast cancer. Physically inactive breast cancer patients had a 33.6% prevalence of diabetes compared with a 37.1% prevalence among physically inactive controls (OR 0.9, 95% CI 0.6 to 1.6).

However, physically active breast cancer patients had a diabetes prevalence of 17.7%, which was significantly lower than in the control group (29.3%, OR 0.4, 95% CI 0.2 to 0.9).

The researchers noted the need for larger studies to confirm their results. With such confirmation, they said, "the reduction in risk among diabetic women, especially those that exercise, may help explain the lower rate of breast cancer among Hispanic women relative to whites."

Practice Pearls:

Explain to patients that Hispanic women with breast cancer were less likely to have diabetes when they exercised regularly.

Department of Defense Era of Hope Meeting: Sanderson M, et al "Diabetes, physical activity, and breast cancer among Hispanic women" Department of Defense Breast Cancer Research Program Era of Hope Meeting 2008.


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