Physical activity shows evidence of beneficial effects on immune system
ARECENT feature in the prestigious Journal of American Medical Association (2008;299(2):160-161) has gained much attention within the medical and health sector. It discussed the evidence supporting moderate exercise training as a strategy to offset compromised immune function in older adults.
Its significance is highlighted by the fact that infections are the leading cause of death for people aged 65 and older. As the human body ages, the immune system becomes less efficient. Consequently, its ability to fight infections and other health issues is diminished in comparison to younger people.
Observational studies suggest the intensity of exercise influences immune system changes. Moderate exercise improves immune functioning by stimulating positive changes in the function and number of various immune system cells, such as the natural killer cell (NK) — one of the body’s first lines of defense against viruses. It also improves the killing capacity of neutrophils — responsible for combating foreign micro-organisms and initiating the immune response.
Intense exercise, on the other hand, appears to suppress immune function. Changes in immune markers during high intensity or prolonged exercise include lower measures of antibodies, depressed NK activity and decreased neutrophil activity.
The benefits of regular physical activity or exercise for both the prevention and management of chronic disease and ill-health are well established. Much of the evidence to date has observed changes in the body’s various systems — primarily metabolic, cardiovascular and musculoskeletal. It is only in recent years that attention has been focusing on the immune system. The impact of exercise on the immune function has important public health consequences and highlights the beneficial effects of exercise on disease prevention and management.
A recent study observing wound healing properties in aged mice, published in the American Journal of Physiology — Regulatory,IntegrativeandComparativePhysiology, revealed that exercise has the ability to reduce the inflammatory response in wounds (2008;294:R179-R184). The author theorised that exercise encourages healing by decreasing local inflammation.
The results may have significant implications for the immune function of people with chronic illnesses, since inflammation underlies the pathophysiology in many diseases including type 2 diabetes, heart disease, arthritis, and Alzheimer’s disease.
Indeed, this may provide further evidence that exercise is a primary therapy for people with diabetes, since its two most common secondary complications are also strongly linked to inflammatory markers. These include the inflammatory C-reactive protein present in heart disease and the inflammatory cytokines in foot ulcers.
Although this is a relatively new area, progress is being made to determine the mechanisms that affect immune functioning through exercise, and more importantly, whether these changes in immune functioning can reduce the risk of developing a disease, or at the very least, delay its progression.
A frequent question concerns exercise during illness. Most clinical authorities in the area of exercise immunology suggest the following:
For head colds (runny nose, sore throat without fever or general aches and pains):
Mild to moderate exercise (eg walking, short jogging period) does not appear to be harmful High-intensity exercise should be avoided Higher-intensity exercise may be resumed a few days after symptoms have ceased
For chest colds, symptoms of fever, extreme tiredness, muscle aches or swollen lymph glands: Avoid exercise during symptoms Commence with light-intensity activity a few days after symptoms have ceased, and allow two to four weeks before resuming higher-intensity exercise
During this period, monitor how you feel during exercise and during the recovery period, to avoid a relapse of symptoms.
The exercise dose range for enhanced immune function is consistent with current physical activity guidelines, including both aerobic and strength exercise. To determine the appropriate exercises and intensity for your circumstances, consult your local exercise physiologist. Chris Tzar is an exercise physiologist and director of the Lifestyle Clinic, Faculty of Medicine, University of NSW www.lifestyleclinic.net.au