It’s Never Too Late to Start Exercising: Physical Activity Prevents Breast Cancer in Postmenopausal Women

According to the World Health Organization, breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death in females. There are different risk factors that have been associated with the development of breast cancer, which can be grouped into genetic and environmental factors:
❖ Genetic factors include: family history, race, early menstruation and/or late menopause, density of breast tissue.
❖ Environmental factors include: parity and age of first pregnancy, use of oral contraceptives (1), hormone replacement therapy, breastfeeding, alcohol and tobacco consumption, obesity, diet and lack of physical activity.

Physical activity provides many benefits affecting the environmental or lifestyle risks mentioned above:
● It promotes weight loss and maintenance of a healthy weight
● Improves lipid profile and insulin metabolism.

In relation to breast cancer, physical activity has been found to decrease circulating estrogen levels which has been associated with a reduced risk of breast cancer. However, it is still not clear the timing, type, intensity, and frequency of exercise which would be required to improve the odds. In this blog I will comment on two studies that have looked at the relationship between exercise and breast cancer.

The first study (2) follows up a large cohort of 95,396 post-menopausal women to observe the relationship between physical activity and breast cancer risk over a span of 20 years. Physical activity data was collected at different points in time and a sum total of energy usage units (MET- metabolic equivalent task) per week was documented. The authors found that higher levels of moderate to vigorous activity both long-term and more close to the menopausal transition age, were associated with lower breast cancer risk. It’s important to note that this study has established the importance of recent exercise in the menopausal age, and ascertained that
higher recent activity seems to exert a protective effect during postmenopausal years, this effect being positive across women of all BMI and hormonal therapy statuses.

The second paper (3) is by Paul T. Williams, Ph.D., whose work has focused on the benefits of running and walking in different types of cancers as well as other conditions such as hypertension. In this study he examined the dose-response relationship between breast cancer mortality and walking and running in a large cohort of 79,124 women during a follow up period
of 11 years. The energy expenditure per week was calculated based on baseline questionnaires collecting data on distance and pace walked or run weekly during the 5 preceding years. During the 11 years of study, 111 women died of breast cancer. The study found that overall risk mortality was 41.5% lower for women whose energy expenditure was at least 7.5 MET, which would be equivalent to about 7 miles of brisk walking or 4.75 miles of running per week. This relationship persisted when adjusted for other collected variables such as education, baseline smoking, alcohol consumption or food group intake, BMI, age of first menstruation, parity,
breastfeeding or family history of cancer.

The take home message from current research is that it is never too late for women in post-menopausal years to improve their physical activity and reduce their risk of breast cancer. The effect seems to be associated with more vigorous forms of exercise, such as brisk walking and/or running. The preventive mechanism of action of exercise seems to be the reduction in the circulating levels of estrogens. However, since it has been found (3) that the same preventive effect holds true in cases where women developed hormone receptor positive and negative tumors, there may be also other protective physiological pathways implicated, such as the improvement of insulin sensitivity and reducing circulating insulin levels, enhancing immune function, or reducing chronic inflammation.

References:

(1) Malone, E. (2019). Oral Contraceptives and Breast Cancer: A Review of the Epidemiological Evidence with an Emphasis on Younger Women. [Accessed 25 Oct. 2019].
(2) Eliassen, A., Hankinson, S., Rosner, B., Holmes, M. and Willett, W. (2010). Physical Activity and Risk of Breast Cancer Among Postmenopausal Women. [Accessed 25 Oct. 2019].
(3) Williams, P. (2013). Breast Cancer Mortality vs. Exercise and Breast Size in Runners and Walkers. [Accessed 25 Oct. 2019].