Breast cancer is the most common cancer affecting women, with 1 in 8 women developing invasive breast cancer in their lifetime. Every year, approximately 322,000 cases are diagnosed, with over 42,000 deaths due to breast cancer. If caught early, the survival rate is 99%! To promote early detection, doctors advise women to get screened for breast cancer genes, undergo routine mammograms, and perform self-exams to identify obvious abnormalities.

But along with these screening methods, a healthy lifestyle is also generally beneficial in preventing conditions like cancer. For a while, doctors and researchers did not know how lifestyle choices influenced whether cells remained healthy or developed into cancer, but recent advances have shed light on these mysteries. The most recent discovery was made by researchers from Jagiellonian University Medical College in Poland. Their work showed that moderate physical activity, like cycling, brisk walking, or water aerobics, improves the function of immune cells that protect against cancer.

Innate and adaptive immunity

It is well known that physical activity reduces the risk of numerous diseases, reduces the side effects of cancer treatments, and improves a patient’s survival. Researchers have long hypothesized that physical activity improves immune cell function, as studies have shown it reduces inflammation. When looking at the two branches of the immune system, innate and adaptive, researchers from Appalachian State University and the University of Copenhagen found that exercise triggers responses from both branches.

In the innate immune system, which is the body's general first line of defense, natural killer cells were stimulated. Natural killer cells, as their name implies, are specialized immune cells that recognize infected or cancerous cells and destroy them. Natural killer cells recognize obvious defects in cells and do not build a “memory” in case the same disease occurs again. This is the role of the adaptive immune system.

In the adaptive immune system, immune cells become “memory” cells that recognize a specific disease’s unique marker, allowing them to detect it more quickly the next time it’s present in the body. For cancers that evade natural killers, cytotoxic (cell-killing) T cells remember the cancer and actively search for it to destroy it. Along with activating natural killer cells, the Appalachian State University and University of Copenhagen researchers found that exercise also activated anti-cancer cytotoxic T cells.

However, there are some caveats with exercising and immune cell activation. When more intensive exercise, such as weightlifting or heavy cardio, is performed, immune cells are activated in the moment to control the inflammation generated by the stress. After the exercise is completed, there are high levels of cortisol and other stress hormones that suppress immune cells, preventing the immune system from benefiting in the long run. To counteract this double-edged sword, the research group from Jagiellonian University Medical College tested whether light to moderate physical activity confers benefits to the immune system for longer periods.

The moderate exercise “sweet spot”

In their study, 141 women aged 20 to 36 years old were monitored using Fitbit watches for two months. Thanks to passes provided by the research team, the women engaged in moderate physical activity at home or at local gyms for three hours each week. By the end of the two months, blood samples were collected, and the researchers looked at the activity levels of natural killer and cytotoxic T cells.

From the Fitbit data, the more steps a woman had in a day, the more natural killer cells that cooperate with the adaptive immune system were present in her bloodstream. If a woman had more active minutes (as indicated by an elevated heart rate during physical activity), there were more natural killer cells in her bloodstream, supporting the innate immune system. Finally, if a woman had more very active minutes per day (such as brisk walking or completing chores), her natural killer cells had greater activity and cytotoxicity, meaning they were more effective. The increase in very active minutes also prevented the overstimulation of natural killer cells by immune signals, thereby protecting against adverse effects and averting off-target killing of cells. Unfortunately, the research team was unable to find an association between moderate physical activity and cytotoxic T cells, but they propose that a longer study could shed light on how these cells are affected.

Preventing problems through simple solutions

Overall, the researchers from Jagiellonian University Medical College confirmed the beneficial effect of physical activity on immune cells and shed light on how moderate physical activity confers these benefits without potential drawbacks. With the focus of this study on women with no recorded health issues, the research team provides evidence that physical activity will stimulate anti-cancer cells to be more effective in policing the body to remove potential threats, including breast cancer. With more time and study, more information can be gathered on how physical activity improves immune cells, and recommendations can be made during doctor’s appointments to prevent the development of breast cancer through simple lifestyle changes.

References

American Cancer Society. (2026, January 13). Breast cancer statistics | How common is breast cancer?.
Feng Y, Feng X, Wan R, Luo Z, Qu L, Wang Q. Impact of exercise on cancer: mechanistic perspectives and new insights. Front Immunol. 2024;15:1474770. pmid:39346906.
Friedenreich CM, Neilson HK, Lynch BM. State of the epidemiological evidence on physical activity and cancer prevention. Eur J Cancer. 2010;46(14):2593–604. pmid:20843488.
Hojman P. Exercise protects from cancer through regulation of immune function and inflammation. Biochem Soc Trans. 2017;45(4):905–11. pmid:28673937.
Gleeson M, Bishop NC, Stensel DJ, Lindley MR, Mastana SS, Nimmo MA. The anti-inflammatory effects of exercise: mechanisms and implications for the prevention and treatment of disease. Nat Rev Immunol. 2011;11(9):607–15. pmid:21818123.
McTiernan A. Mechanisms linking physical activity with cancer. Nat Rev Cancer. 2008;8(3):205–11. pmid:18235448.
Nieman DC, Wentz LM. The compelling link between physical activity and the body’s defense system. J Sport Health Sci. 2019;8(3):201–17. pmid:31193280.
Pedersen BK, Hoffman-Goetz L. Exercise and the immune system: regulation, integration, and adaptation. Physiol Rev. 2000;80(3):1055–81. pmid:10893431.
Tubek-Krokosz A, Baran J, Galbarczyk A, Gałuszka-Bulaga A, Klimek M, Krzych-Miłkowska K, et al. (2026) The effect of moderate physical activity on NK cells populations and cytotoxic T lymphocytes in young, healthy women. PLoS One 21(5): e0349215.
Walsh NP, Gleeson M, Shephard RJ, Gleeson M, Woods JA, Bishop NC, et al. Position statement. Part one: Immune function and exercise. Exerc Immunol Rev. 2011;17:6–63. pmid:21446352.