Does exercise blunt your immune system?
This depends on the intensity of your exercise. Workouts can actually enhance your ability to fight infection by increasing your antibody and natural killer cell response. Typically, this applies to short-term (20 to 30 minutes) of exercise at a moderate intensity.
In addition, after a moderate bout of exercise, your immune system's surveillance is enhanced for approximately 2 to 3 hours. This is due to the production of interleukin and interferon, antiviral molecules that stimulate the activity of lymphocytes.
One scientific study explored the effects of moderate exercise on immunity and demonstrated that fitness can reduce the severity of symptoms associated with the common cold. Individuals who were physically active, had a healthy body weight, and consumed a diet rich in fruits and vegetables had 33 percent fewer sick days and less cold symptoms than inactive, overweight, counterparts.
Your immune system might be at risk if you take on a higher-intensity routine when sick. Your body relies on carbohydrates for energy during intense workouts. Your body fatigues and reduces intramuscular carbohydrate stores. Your body secretes stress hormones that have a negative effect on immune cell production. After a bout of intense exercise, your immune system may be depressed due to a reduction in lymphocyte production.
As a result, your body may be less efficient to clear pathogens and viruses. This may last between 3 to 72 hours post-exercise.
What about working out in the cold?
There are two prevalent misconceptions about exercising in cold. The first is that working out in the cold increases your risk of getting sick. First, cold weather doesn't make people sick. As mentioned above, when the body is under stress it releases hormones that reduce the efficiency of the immune system.
Prolonged shivering due to poor clothing choices (or wet clothing) and inadequate nutrition (low-carbohydrate content) will result in an increased stress on the body and possibly a higher chance of getting sick.
The second misconception is that exercise in the cold burns more calories. When not dressed appropriately for cold-weather workouts your body will start to shiver, which burns approximately 10 percent more calories per hour than if you dressed properly. The danger associated with this practice outweighs the minimal benefit, burning an extra 50 calories per hour.