Physical Activity and Immune Function

Exercise and health go hand in hand. People who exercise on a regular basis, or who are physically active throughout the day, tend to get sick less often and live longer. There is a long list of health benefits associated with physical activity, everything from lowering high blood pressure, to losing extra weight, to improving sleep and mood, to maintaining function and independence as we age. And there is evidence that regular exercise might also positively affect immune function.

Renewed interest in the relationship between physical activity and immune function has grown out of the HIV epidemic. Several studies have demonstrated that persons with impaired immune systems can exercise safely without risk to their health, and in fact, can enhance their emotional well-being as well. In these studies, exercise also seemed to increase numbers of certain immune cells that help to bolster immune activity.

It appears that regular exercisers don’t get sick as often as less active people. Evidence indicates that a J-curve relationship exists between the intensity of exercise and the risk of upper respiratory tract infection (URTI) (colds and flues). Moderate exercise (brisk walking) may decrease the risk of URTI below that of a sedentary person, but high-intensity exercise (running and/or training for marathons and ultra-marathons) may raise the risk above average.

Immune system changes that apparently are related to the intensity of exercise have been identified. Moderate endurance exercise, such as brisk walking, stimulates positive changes in the function and numbers of various immune system cells, such as natural killer cells (NK) one of the body’s first lines of defenses against viruses. It is also associated with prolonged improvement in the killing capacity of neutrophils, one of the most efficient phagocytes (cells that kill foreign microorganisms and initiate the immune response). These changes may be related to the release of hormones such as endorphins and enkephalins that help to regulate immune function.

On the other hand, high intensity exercise may have a negative impact on immune function. Immune marker changes that suggest the increased risk for high intensity exercise include, lower measures of immunoglobulins (antibodies) like those found and measured in saliva, depressed NK cell activity and decreased neutrophil phagocytic activity. These negative effects may also be related to the release of stress related hormones such as cortisol and ACTH which have immunosuppressive characteristics.

High intensity exercise is also associated with muscle cell damage and inflammation. The immune system is involved with tissue repair. It is theorized that while the immune cells are busy with the repair process, host protection may suffer. There appears to be a window of opportunity for infection during recovery from high-intensity exercise. Consequently, rest, good nutrition and hydration are recommended after bouts of vigorous exercise to allow the body to recover, and moderate exercise may be the better choice for enhancing health and well-being.

Growing interest in complementary medicine and the self-help movement has also spurred interest in the benefits of exercise in cancer treatment. Epidemiological studies have reported a reduced incidence of cancer in physically active groups. The research suggests that physical activity has a protective affect against the risk of developing some cancers, most notably cancers of the colon, breast, prostate and reproductive system. NK cells and microphages (another phagocyte) are involved in the first line defense against the development and spread of tumors. Exercise seems to enhance the efficiency of both these cell types, helping the body fight against tumor growth. Current hormone and exercise research is providing hopeful insight into other possible biological markers and how physical activity may affect tumor development and regression.

People often ask if it’s okay to exercise if you have a cold or are not feeling well. Here are some suggestions:

• If you have a cold, not feeling well from the neck up, it’s okay to continue exercising. Just decrease the intensity, keep it comfortable and monitor how you feel during and after exercise.
• If the symptoms extend over your whole body (fever, muscle aches, excess fatigue), stop exercise until feeling better, and resume exercise slowly, allowing about 2 weeks for resumption of usual exercise level to avoid relapse or complications.

How much exercise is necessary to appreciate healthy benefits? Generally, moderate exercise, including both aerobic and resistance training is recommended:

• Aerobic: 30-60 minutes, 3-5 times per week, brisk (comfortable but challenging)
• Resistance training: 1-2 sets of 8-12 repetitions, 8-10 different exercises, 2-3 times per week, moderate effort

However, if this seems like an impossible task, then simply consider increasing physical activity throughout the day. Although everything counts, and something is better than nothing, try to accumulate 30 minutes of brisk activity throughout the day, in at least 10 minute segments. That works out to 3-4 hours per week and can include activities such as housework, yard work, gardening, play with your children, climbing stairs, and walking for errands.

It seems reasonable to assume that exercise and physical activity are essential components of a health promoting lifestyle, both for generally healthy individuals as well as people with chronic illness. It has both protective as well as bolstering affects on the immune system. Exercise increases specific immune system markers and biologically provides a protective effect on the body. We all know that exercise is good for us and research continues to show us some possible reasons why.

Remember: before you embark on any exercise program you should discuss it with your medical professionals.

As printed in the VHL Family Forum  9:1, March 2001.  For permission to reprint, please contact VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org.