Can Too Much Exercise Decrease Your Immunity?

Black athlete running in race
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Research has found a link between moderate exercise and a strong immune system. However, studies have also found an increased risk of illness in those who participate in intensive exercise. These seemingly contradictory findings leave many athletes wondering whether their fitness training helps or hurts their body's immune function.

The truth is that scientists don't fully understand the exercise-immune relationship. Much of the research investigating the connection is relatively new and is still quite controversial. While some researchers provide evidence for a link between hard exercise and reduced immunity, others say that the data is misunderstood. But almost all scientists agree that more research is needed to finalize an answer.

Exercise and Immunity

The average adult has two to three upper respiratory tract infections (URTIs) each year. We are exposed to viruses all day long, but some people seem more susceptible to catching colds or the flu. Could exercise play a role? It may, but there are a number of interconnected factors to take into consideration. Two important factors are exercise intensity and workout duration.

Moderate Exercise

Even though exercise immunology is a relatively new field (most papers on the topic have been published after 1990), most of the data support a positive relationship between exercise and changes to the immune system. But the exercise "dose" matters. When moderate exercise lasts less than 45–60 minutes, there are both short and long-term benefits.

"There is a general consensus that regular bouts of short-lasting (i.e., up to 45 minutes) moderate-intensity exercise is beneficial for host immune defense, particularly in older adults and people with chronic diseases."

—Exercise Immunology Review (2020)

In the short term, a single dose of exercise reduces stress hormones. And researchers have observed other benefits including improved immunosurveillance and lower inflammation. Scientists have found that these benefits may be of particular value for those who are obese or are managing disease.

According to professor David Nieman of Appalachian State University, when moderate exercise is repeated on a near-daily basis there is a cumulative effect that leads to long-term immune response. His research shows people who walk 40 minutes per day at 70% to 75% of their VO2 max experience half as many sick days due to sore throats or colds as people who don't exercise.

In the longer term, moderate exercise also promotes small anti-inflammatory effects and can improve glucose and lipid metabolism. Scientists have reported lower chronic low-grade inflammation, and improved immune markers in several diseases including cancer, HIV, cardiovascular disease, diabetes, cognitive impairment, and obesity.

Lastly, researchers have observed that there may be an enhanced antibody-specific response when vaccinations are preceded by a single bout of moderate exercise, although more research is needed to fully understand that benefit.

Vigorous Exercise

Research regarding vigorous, sustained exercise has been less consistent. While there are clear associations between heavy training loads and decreased immunity, it is not clear if exercise causes immune suppression.

Some early evidence in the field of exercise immunology suggested that too much intense exercise can reduce immunity. Research showed that more than 90 minutes of high-intensity endurance exercise can make athletes susceptible to illness for up to 72 hours after the exercise session. During intense physical exertion, the body produces certain hormones that may temporarily lower immunity.

And more recent research suggests that repeated bouts of strenuous exercise have been associated with suppressed immune function, increased symptoms of upper respiratory tract infections (URTI), latent viral reactivation, and impaired immune responses to vaccines. This type of immune suppression is most commonly seen in athletes and other high-performance personnel, such as military members.

Many researchers in the field of exercise immunology believe that repeated bouts of arduous high-intensity exercise lasting over two hours can compromise the immune system.

As an example, there have been repeated reports of marathon runners experiencing higher than normal rates of illness in the weeks shortly before and shortly after their race. But some scientists argue that the data has been incorrectly interpreted.

Authors of a 2018 report said that several of the marathon studies had shortcomings and need reevaluation. More specifically, they argue that some cellular changes that were originally reported to be detrimental to immune function were actually signs of improved immune function. Their report attempts to debunk several long-held beliefs that exercise can impair immune health.

Because there have been significant research findings on both sides of the aisle, authors of the 2020 report on exercise and immune function sought out arguments from those who feel exercise promotes immune health and those who feel it may not. Both sides agreed on two things: that there are many other factors impacting immune health in athletes and that more research is needed.

Other Factors

Authors of the 2018 research report wrote that the reports linking marathon participation to increased illness risk did not take into account the impact of large group gatherings. They provide evidence that attendance at any mass participation event is likely to increase the risk of acquiring an infectious illness.

Other researchers in the field point to other issues such as stress, lack of sleep, nutrition, and hygiene factors that play a role in whether or not an athlete gets sick. The following factors have all been associated with impaired immune function and increased risk of catching colds:

  • Cigarette smoking
  • Fatigue and lack of sleep
  • Poor nutrition
  • Older age
  • Overtraining syndrome
  • Stress

In short, while researchers seem to agree that there is a link between certain types of infections (most notably upper respiratory tract infections) and intensive training, they can't say for sure that exercise is the cause of the increased risk because there are too many other factors involved.

Tips to Boost Immune Health While Training

There are some things that seem to protect us from catching colds and the flu. One of those things appears to be moderate, consistent exercise. Research continues to support a link between moderate, regular exercise and a healthy immune system.

If you ramp up your training for a competitive event or other reasons, keep a few common-sense tips in mind to reduce your odds of getting sick. Several athletic organizations, including the International Olympic Committee, have provided recommendations that you can use to guide your training plan. 

Increase Training Incrementally

Follow a detailed, individualized training and competition plan. Consider working with a qualified coach to develop a plan that suits your individual health and lifestyle to achieve balance. Increase training intensity in small increments (typically less than 10% per week) and create a competition calendar based on your ability and overall health.

Rest Properly

Remember to include enough rest days to allow your body's immune system to recover. If you are feeling run-down or have other symptoms of overtraining syndrome—such as increased resting heart rate, slow heart rate recovery after training, mood changes, and fatigue—you may need to tone down your workouts as well.

In addition, be sure to get enough sleep. Avoid alcohol (which can impair sleep) and practice good sleep hygiene: Try to follow a regular sleep schedule, minimize electronic use at bedtime, and create a cool, dark, sleep environment.

Manage Illness

If you are already ill, you should be careful about exercising too intensely. In general, if you have mild cold symptoms and no fever, light or moderate exercise may help you feel a bit better and actually boost your immune system. Intense exercise, however, will only add more stress to your already taxed immune system, undermining your recovery.

Minimize Germ Exposure

Reduce your exposure to germs and viruses by choosing workout spaces that are well ventilated and cleaned often. When training hard, minimize exposure by avoiding close contact with those who might be sick, steering clear of crowded, enclosed spaces, and not sharing drinking or eating utensils.

Practice Good Hygiene

Other hygiene practices can also help. Wash your hands often and sneeze or cough into the crook of your elbow. Also, reduce your own hand-to-face contact.

Experts advise using safe sex practices (including the use of condoms) and avoid wearing open footwear when using public facilities to limit skin infections. To minimize the risk of insect bites, use insect repellents, and cover your arms and legs with clothing at dawn or dusk.

Eat Well

Researchers in almost all published studies report a relationship between diet and the health of athletes. Guidelines suggest that you should consume a nutritious diet with enough calories to maintain a healthy weight. Focus on grains, fruits, and vegetables to benefit from adequate carbohydrates and polyphenols that reduce exercise-induced inflammation and improve viral protection.

Reduce Stress

Stress is a normal part of competition. But managing day-to-day stress can help you to maintain a healthy immune system. Use stress management techniques, such as meditation or deep breathing to maintain calm as needed. And work with a behavioral health specialist to develop coping strategies to minimize the impact of negative life events and emotions.

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Article Sources
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