Posted by: Maria/MDHealthForum.com Team

Breast cancer is the second most common type of cancer among women. The American Cancer Society estimates that about 1.3 million women will be diagnosed with breast cancer annually worldwide. Since 1990, breast cancer mortality rates in the US have been declining steadily. Experts speculate that earlier detection and better treatments contribute to the decline in mortality rate. Risk factors for developing this disease have been identified through studies. Some systematic reviews suggest that there is an inverse association between physical activity and breast cancer risk. Recently, the findings of an 11- year U.S. prospective study on postmenopausal women was published. According to this National Cancer institute study, vigorous exercise can reduce a woman’s risk of breast cancer.

A team of researchers led by Michael F. Leitzmann, examined the data of over 32,000 postmenopausal women who were enrolled in the Breast Cancer Detection Demonstration Project Follow-up Study. Included in the data were responses to a questionnaire about their physical activity throughout the previous year. The subjects were asked to estimate the number of hours they spent per day engaging in moderate and vigorous physical activity. The following were considered as moderate or non-vigorous activity: light housework, lawn mowing, gardening, light sports or exercise, bicycling on level ground, golf, light jogging and recreational tennis. Examples of vigorous activity in the questionnaire included: heavy housework such as scrubbing floors or washing windows, heavy yard-work, chopping wood, strenuous sports or exercise, fast jogging, competitive tennis, bicycling on hills and fast dancing. Postmenopausal breast cancer cases were identified through self-reports, death certificate and state cancer registries. During the 11-year period, 1506 new cases of postmenopausal breast cancer were reported.

Based on the result of the study, non-vigorous activity did not seem to protect against breast cancer. However, normal-weight women who engaged in the highest amount of vigorous activity, displayed a significant decrease in breast cancer risk. Investigators found out that the risk of this group was reduced by a third. Additionally, their findings show that overweight women who engaged in strenuous exercise did not show reduction in breast cancer risk. The researchers did not look at why exercise may benefit postmenopausal women but they noted that previous studies have proven that exercise decreases estrogen levels which known to contribute to the risk of primary breast cancer.

Sources:
Journal of Clinical Oncology, May 1, 2007

Michael F Leitzmann, Steven C Moore, Tricia M Peters, James V Lacey, Arthur Schatzkin, Catherine Schairer, Loiuse A Brinton and Demetrius Albanes
Prospective study of physical activity and risk of postmenopausal breast cancer

Breast Cancer Research 2008, 10:R92doi:10.1186/bcr2190 published 31 October 2008
Ries LAG, Melbert D, Krapcho M, et al., eds, SEER Cancer Statistics Review 1975-2004, National Cancer Institute. Bethesda, MD, based on November 2006 SEER data submission.