Exercise and Immunity

Study proves exercise boosts immune system

“Research has shown that during

moderate exercise, several positive

changes occur in the immune system.

Although the immune system returns to

pre-exercise levels very quickly after the

exercise session is over, each session

represents a boost that appears to reduce

the risk of infection over the long term.”

Based on current knowledge, good immune function

can be maintained by regular physical activity, eating a

well-balanced diet, keeping life stresses to a minimum,

avoiding chronic fatigue, and obtaining adequate sleep.

"We know that people who exercise regularly have lower levels of stress hormones in the blood, and there's a definite link between low levels of stress hormones and improved immunity"

The average adult has two to three upper respiratory infections each year. We are exposed to viruses all day long, but some people seem more susceptible to catching colds or the flu. The following factors have all been associated with impaired immune function and increased risk of catching colds:
  • old age
  • cigarette smoking
  • stress
  • poor nutrition
  • fatigue and lack of sleep
  • over-training

Regular Moderate Exercise Boosts Immunity
However, there are some things that seem to protect us from picking up colds. One of those things appears to be moderate, consistent exercise. More and more research is finding a link between moderate, regular exercise and a strong immune system.

Early studies reported that recreational exercisers reported fewer colds once they began running. Moderate exercise has been linked to a positive immune system response and a temporary boost in the production of macrophages, the cells that attack bacteria. It is believed that regular, consistent exercise can lead to substantial benefits in immune system health over the long-term.

More recent studies have shown that there are physiological changes in the immune system as a response to exercise. During moderate exercise immune cells circulate through the body more quickly and are better able to kill bacteria and viruses. After exercise ends, the immune system generally returns to normal within a few hours, but consistent, regular exercise seems to make these changes a bit more long-lasting.

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

Too Much Exercise May Decrease Immunity
However, there is also evidence that too much intense exercise can reduce immunity. This research is showing 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. This is important information for those who compete in longer events such as marathons or triathlons.

Intense exercise seems to cause a temporary decrease in immune system function. Research has found that during intense physical exertion, the body produces certain hormones that temporarily lower immunity.

Cortisol and adrenaline, known as the stress hormones, raise blood pressure and cholesterol levels and suppress the immune system. This effect has been linked to the increased susceptibility to infection in endurance athletes after extreme exercise (such as marathon running or Ironman-distance triathlon training).

If you are training for ultra-endurance events, a key component of your training should be including enough rest and recovery days to allow your body (immune system) to recover. If you are feeling run-down or have other symptoms of overtraining syndrome --such as increased resting heart rate, slower recovery heart rate, irritability or general heaviness and fatigue -- you may need to tone down your workouts as well.

If you are already ill, you should be careful about exercising too intensely. Your immune system is already taxed by fighting your infection, and additional stress could undermine your recovery. 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 will only make things worse and likely extend your illness.

See: Should I Exercise with a Cold or the Flu?

Psychological Stress Also Reduces Immunity
It's not only physical stress that increases the release of cortisol and adrenaline. Psychological stress can also impair immunity and lead to an increase of cold and flu infections.

Researchers at Ohio State followed people who had the stress of caring for a loved one with Alzheimer's disease and found that they experienced twice as many colds as non-caregivers. For such individuals, there is clearly a physical benefit to moderate, regular exercise.

The immune system and its role in chronic fatigue syndrome (CFS)

In many diseases, ranging from autoimmune diseases to AIDS and CFS, there is evidence of mild to severe dysfunction of the immune system. An impaired immune system weakens the body's ability to fend off infection and malignancy, but the immune system can also produce symptoms such as fever, weight loss, musculoskeletal pain and fatigue. In fact, many of the symptoms of the flu (such as achy muscles and joints, fever, and headache) are caused by the immune system's response to the infection.

Exercise and immunity

Even more so than nutrition, exercise has the capacity to protect and even enhance the immune response. Experimental studies have shown that a regular exercise program of brisk walking can bolster many defenses of the immune system, including the antibody response and the natural killer (T cell) response.

Fortunately, the intensity and duration of exercise needed to support the immune system is less than that needed to provide the best cardiovascular training. Thus, even relatively low levels of aerobic exercise can protect your immune system. Twenty to 30 minutes of brisk walking five days per week is an ideal training program for maintaining a healthy immune response.

Exercise can also improve your mental wellness. Regular aerobic exercise can help relieve mild to moderate degrees of depression and anxiety. People who exercise also have less loneliness and anger, and are better able to control their own destiny. It is not clear whether exercise boosts the immune system directly or works through a link with the brain and nervous system.


Benefits of Exercise - How does exercising at a moderate level improve our immune system?

Light or moderate exercise boosts our body’s natural immune system by circulating protective cells through the body faster, to attack and eliminate bacteria, viruses and fungi. Infection fighters, such as Natural Killer Cells, macrophages, immunoglobins, white blood cells, and other antibodies, are produced in the bone marrow, lungs, and spleen, and have a clean up effect on foreign invaders.

Another theory holds that the increase in body temperature when we exercise may inhibit the growth of bacteria, thus reducing its foothold in the body. Some exercise scientists believe that regular exercise helps rid the lungs of airborne bacteria and viruses that cause URTI, while others believe exercise causes the loss of carcinogens through increased sweat and urine loss.

In the mice at the University of Illinois, moderate exercise subtly hastened the shift from a T1 response to a T2-style immune response — not by much, but by just enough, apparently, to have a positive impact against the flu. “Moderate exercise appears to suppress TH1 a little, increase TH2 a little,” Woods says.


• Individuals using garlic were almost two-thirds

less likely to catch cold than those receiving


• Furthermore, participants who did catch cold

recovered about one day faster in the garlic

group as compared to the placebo group.

Several theories help to explain the relationship between moderate exercise and the immune system.

First, it appears that regular physical activity might contribute to ridding the lungs of the types of airborne bacteria and viruses that are linked to common upper respiratory tract infections, while also cleansing the body of certain carcinogens (cancer-causing cells) and waste products through increased output of urine and sweat.

Second, the increase in blood flow associated with moderate exercise helps to more quickly circulate antibodies and white blood cells needed to fight infection, thus providing the body with an early warning system to fight off potentially damaging germs.

In addition, the increase in body temperature that results from physical activity might aid in inhibiting the growth of bacteria, allowing the body to fight infection more effectively.

Finally, moderate exercise has been shown to reduce the secretion of stress-related hormones thought to contribute to the onset of illnesses such as the flu and the common cold, and give a temporary boost in the production of macrophages, the cells that attack bacteria.

Dr. Nieman, of Appalachian State University, says that during exercise, two types of immune cells circulate more freely in the blood, neutralizing pathogens. Although the immune system returns to normal within three hours, the effect of the exercise is cumulative, adding up over time to reduce illness rates, he says. He compares the process to "a cleaner who comes in for an hour a day, so by the end of a month, your house looks much better."