Exercise and Immunity

Can Too Much Exercise Make You Sick?

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.

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.

Should I Exercise With a Cold?

The average adult has two to three upper respiratory infections each year. Many athletes wonder if they should continue their training routine when sick. While research is limited, most experts recommend that if your symptoms are above the neck and you have no fever, exercise is probably safe. Intensive exercise should be postponed until a few days after the symptoms have gone away. However, if there are symptoms or signs of the flu, such as fever, extreme tiredness, muscle aches, swollen lymph glands, then at least two weeks should probably be allowed before you resume intensive training.

Other Tips to Prevent Illness:

• Eat a well-balanced diet. The immune system depends on many vitamins and minerals for optimal function. However, at this time, there is no good data to support supplementation beyond 100 percent of the Recommended Dietary Allowances. A good rule is to eat 10-15 calories per pound of "desired body weight." If your ideal weight is 170 lbs, then consume 1700-2550 calories a day (1700 for sedentary individuals and 2550 for extremely active types.)
• Avoid rapid weight loss. Low-calorie diets, long-term fasting and rapid weight loss have been shown to impair immune function. Losing weight while training heavily is not good for the immune system.
• Obtain adequate sleep. Major sleep disruption (e.g., three hours less than normal) has been linked to immune suppression.
• Avoid over-training and chronic fatigue. Space vigorous workouts and race events as far apart as possible. Keep "within yourself" and don’t push beyond your ability to recover.
• Wash your hands frequently. This is often your best prevention. Don't forget your fingernails.
• Avoid putting your hands near your eyes, nose or mouth. Most bacteria and germs are spread from a surface to your hands to your face not by air.
• Get a flu shot. Especially if you have a weakened immune system.Get enough sleep. Lack of sleep can reduce immune functioning making you susceptible to sickness.
• Drink more water. In the fall and winter, it is easy to overlook your thirst and get dehydrated. Make sure you consume 8 glasses a day.
• Continue a moderate exercise program. Try to maintain a consistent exercise routine
• Limit alcohol intake. Alcohol can be dehydrating which, in turn, may decrease your resistance to bacteria.
• Finally, listen to your body. If you are less than 100% you will feel better and recover faster if you let yourself rest.

Resource from: http://sportsmedicine.about.com