Experts have recognized that active lifestyles favor lower breast cancer risk. However, despite this long-standing appreciation, the precise mechanistic link between breast cancer and exercise remains elusive. So, does physical activity actually protect from breast cancer? Data recently published in the British Journal of Sports Medicine suggests that when it comes to breast cancer, exercise is, in fact, protective, not just relative.
The study uses a statistical method called Mendelian randomization (MR). This tool measures variation in genes with known functions to evaluate the causal effect of a modifiable exposure on disease, such as time spent being sedentary. MR determines cause and effect by simulating randomized trials based on genotype. The researchers used this method to question if an active lifestyle, determined by the amount of time spent in physical activity, protects from the development of breast cancer. Specifically, the study investigated the effect of genetic variations associated with risk factors, including lifelong physical activity and spending a significant amount of time sedentary.
The researchers extracted data from 76 different studies associated with the Breast Cancer Association Consortium. The many studies consulted resulted in the inclusion of over 130,000 women of European ancestry. The participants in the study included nearly 70,000 women with invasive breast cancers and over 6,000 women with in situ breast cancers. The researchers also obtained data from about 54,000 women without breast cancer to serve as controls in the study.
The researchers used DNA to predict overall activity based on single nucleotide polymorphisms (SNPs) identified in a previous study. Additionally, participants wore devices on their wrists to measure physical activity and sedentary time. Vigorous physical activity was measured with either the wrist-worn accelerometer or with self-reporting by participants.
The study revealed that women with high overall activity have a lower risk of developing breast cancer. This finding was consistent when examining overall breast cancer risk as well as in many subgroups of breast cancer patients. Those with more sedentary time were at elevated risk of hormone-receptor-negative (HR-) breast cancers. Notably, women spending a lot of time sedentary exhibited a 104% greater risk of developing triple-negative breast cancer.
The authors conclude that greater overall physical activity, more vigorous activity, and less sedentary time are likely to reduce breast cancer risk. They suggest that implementing more active lifestyles may reduce breast cancer burden. Because breast cancer remains the most frequently diagnosed cancer in women in the United States, lifestyle modifications that decrease sedentary time could significantly benefit the cancer burden nationally.
While doctors already recommend an active lifestyle to prevent many cancers, including breast cancer, these findings suggest a reduction in future breast cancer diagnoses if an active lifestyle is adopted. So, stand up when you can, take a walk around the block if you’re able, and exercise when possible!
Sources: Br J Sport Med, Nat Commun, CA
