How Exercise Impacts Your Immune System

Exercise at all intensities produces some pro-inflammatory cytokines, which may help to clear infections and reduce inflammation. A 2020 review in Frontiers in Physiology found that, although moderate-intensity and vigorous-intensity exercise release pro-inflammatory cytokines, anti-inflammatory ones are subsequently released to fight that response.

Although it's not completely clear how pro-inflammatory cytokines from exercise can be beneficial, Heffron said, it's probably due to the way they rise and fall after exercise.

Additionally, exercise decreases stress hormones, which may provide some protection against illnesses, said Tracy Zaslow, MD, a sports medicine physician at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles and team physician for Angel City Football Club. During a workout—as well as after it—body temperature is elevated, and this is thought to help the body fight infection better, she said.

Research shows that exercise can also help decrease pro-inflammatory cytokines in cancer survivors. A 2019 review in the journal Brain, Behavior, and Immunity suggests that doing combined aerobic and resistance training can help reduce pro-inflammatory markers in prostate and breast cancer survivors by increasing lymphocytes, including natural killer, or NK, cells.

During exercise, the body also releases hormones that stimulate the release of lymphocytes (a type of white blood cell) to different organs and tissues, where they can detect viruses and prompt the body to fight them off, Heffron said.

"White blood cells and antibodies are two players in the body's immune system that fight infections", Zaslow said. "Exercise causes changes in antibodies and white blood cells, causing them to circulate more rapidly, so theoretically they can detect illnesses earlier".

Aerobic exercise can stimulate bone marrow to produce white blood cells while increasing the turnover of older cells, Heffron said.

In addition, a 2011 study in the British Journal of Sports Medicine found that people who worked out five or more days a week reduced their chances of developing an upper-respiratory tract infection by 43 percent over 12 weeks compared with sedentary folks.

Oxidative stress is a phenomenon that occurs in the body when there's an imbalance of antioxidants and molecules known as free radicals. While oxidative stress is a natural by-product of the body's biological processes—like breathing, digesting food and even exercising—chronic exposure to high levels of oxidative stress can be harmful.

In fact, it's associated with health conditions such as diabetes, heart disease and cancer. That's because accumulating too many free radicals in the body without enough antioxidants to regulate them can cause cell and tissue damage, which can lead to disease, per a review article in Frontiers in Physiology.

While exercise can be a cause of oxidative stress, it can also fortify the body's antioxidant capacity to fight the negative effects of oxidative stress from all sources—not just from working out, Heffron said. Think of it as a checks-and-balances system.

"Physical activity, whether it's planned, structured training or body movement that occurs with everyday activity, can alleviate the harmful effects caused by free radicals", Zaslow said.

Moderate exercise can help prevent oxidative stress and protect against diseases with low-grade inflammation, such as atherosclerosis (plaque build-up in the heart's arteries), she said.

Exercise is also associated with a reduced incidence of some age-related chronic diseases, including heart disease, type 2 diabetes and some cancers, according to a 2013 review in Clinics. According to a 2019 review in Frontiers in Physiology, strength training is just as effective as aerobic exercise in reducing the risk of chronic disease in older adults—all the more reason to hit the weights.

FYI, moderate-intensity exercise looks different for everyone and is based on individual fitness level. For most people, this includes any type of workout or exercise that elevates the heart rate 50 to 60 percent higher than the resting rate, according to the Cleveland Clinic.

If you're not sure what type of exercise to do (or how much), it's best to chat with your doctor to determine a routine that works for your needs.