Regular exercise—light, moderate, or vigorous—makes the immune system more effective in fighting breast cancer.
How exercise helps the immune system
Aerobic exercise influences the way our bodies break down estrogens to produce more of the ‘good’ metabolites that lower breast cancer risk. Exercise, especially when combined with a needed 5% weight loss in obese women, substantially lowers inflammatory markers and some hormones involved in breast cancer.1Killer-T lymphocytes are special white cells that destroy cancer cells and viruses. Exercise can actually remodel the immune system, making it more effective at fighting disease. After chemotherapy, most T cells become senescent, with reduced ability to fight infections and cancer cells. In one study, cancer patients were given 12 weeks of cardiovascular exercise, strength and endurance training, and flexibility, posture, and balance exercises. The results post-exercise? There were fewer senescent T- lymphocytes and more T- cells that could turn into effective fighters. In other words, regular exercise seems to assist the body in getting rid of T cells that aren’t helpful, making room for T cells that might be helpful. Please note: natural killer cells also destroy cancer cells and viruses. Regular, consistent exercise also improves their efficacy in cancer patients.2
How much exercise?
Postmenopausal women who in the past four years had undertaken regular physical activity equivalent to at least four hours of walking per week had a 10% lower risk for invasive breast cancer compared with women who exercised less during those four years.3 A daily walk for 30 minutes is associated with a lower risk of breast cancer. These results were independent of body mass index, weight gain, waist circumference, and the level of activity from five to nine years earlier.
Walking at a moderate pace for at least 7 hours per week is associated with a 14% lower risk of developing breast cancer after menopause compared to those who walked for 3 hours or less a week. The most active women — those who walked and did more vigorous exercise — had a 25% lower risk of breast cancer compared to the least active. This study included both normal-weight women and obese women. Here, exercise reduced the risk of both estrogen receptor-positive and estrogen receptor-negative cancers. (In estrogen receptor-positive breast cancer, the female hormone estrogen promotes the growth of the cancer.) Some of the women in this study were taking medicine that might have blocked estrogen.
Exercisers tolerate breast chemo better.
Both low and moderate exercise help women tolerate chemotherapy for breast cancer better. Women with breast cancer who follow a physical exercise program during their chemotherapy treatment experience fewer side effects, such as fatigue, reduced physical fitness, nausea, and pain.
More than exercise
World Cancer Research Fund (WCRF) and American Cancer Society (ACS) cancer prevention guidelines recommend maintaining a healthy weight, undertaking at least 150 minutes of moderate-intensity exercise per week, limiting alcohol consumption, and eating a plant-based diet. Weight control throughout life appears to prevent cases after menopause. Observational data link adherence to physical activity and alcohol guidelines throughout life to a reduced risk of developing pre- and postmenopausal breast cancer.
Recent expert reports estimate that successful lifestyle changes could prevent 25% to 30% of cases of breast cancer. Interventional studies involving breast cancer survivors found that lifestyle changes in the form of healthy eating and regular exercise can decrease biomarkers related to breast cancer recurrence and mortality.
Disclaimer: The information in this article is general and educational in nature. Wildwood Sanitarium, its entities, or authors do not intend this information as a substitute for proper diagnosis, treatment, or counseling from a qualified medical provider who knows the person’s medical history and laboratory work.
Copyright © by Wildwood Sanitarium, Inc. 2026. All rights reserved.
References:
- Neilson HK, Conroy SM, Friedenreich CM. The Influence of Energetic Factors on Biomarkers of Postmenopausal Breast Cancer Risk. Curr Nutr Rep. 2013 Dec 15;3(1):22-34.https://pmc.ncbi.nlm.nih.gov/articles/PMC3921460/ [↩]
- Kim JJ, Shin YA, Suk MH. Effect of a 12-week walking exercise program on body composition and immune cell count in patients with breast cancer who are undergoing chemotherapy. J Exerc Nutrition Biochem. 2015 Sep;19(3):255-62. doi: 10.5717/jenb.2015. https://pmc.ncbi.nlm.nih.gov/articles/PMC4624127/ [↩]
- Eliassen AH, Hankinson SE, Rosner B, Holmes MD, Willett WC. Physical Activity and Risk of Breast Cancer Among Postmenopausal Women. Arch Intern Med. 2010;170(19):1758–1764. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/226133[↩]