Sports and the immune system

What's the connection between intensive exercise and getting sick? Find out how athletic training can affect the immune system.

If it seems as if someone on the team always seems to get a cold or runny nose after a competition, then you're not the only one making that observation. Over the years, doctors and researchers have noted that common cold symptoms — stuffy or runny nose, sore throat, fever, and feeling tired — occur more frequently during and after periods of intense training or competition. This seems to be especially true when it comes to endurance sports, such as cycling or long-distance running.

What's the connection between intensive exercise and getting sick? It starts with the way athletic training can affect the immune system.

Physical stress and other training challenges

Studies suggest that a bout of intensive exercise, especially long-duration endurance activity, can temporarily depress the immune system, increasing the risk of upper respiratory tract infections — such as the common cold — in the following week. This can be due to several different ways that intense physical challenge or stress affects the body, including:

  • An alteration in the number and function of circulating immune cells
  • An increase in the levels of stress hormones, such as cortisol
  • An upset in the balance of pro- and anti-inflammatory immune proteins (cytokines)

In addition to physical stress, other factors likely contribute to making the immune system more vulnerable.

  • Psychological stress. In general, exercise tends to relieve mental and emotional tension. But someone who is already under chronic stress — for example, because of competition, a busy schedule or too little time to relax — can be more vulnerable to the effects of exhaustive training.
  • Sleep disruption. Elite athletes often travel for competition, which can lead to jet lag and time zone dislocation. This can wreak havoc on the regular sleep-wake schedule. Not getting proper rest, both in terms of quantity and quality, can diminish the immune system's ability to fight off infection and adapt to changing conditions.
  • Energy deficiency. To operate at its best, the immune system needs fuel just like the rest of the body. Not consuming enough calories in a balanced diet — with appropriate amounts of carbohydrates, protein, fats, vitamins and minerals — can impair immune function.

Immune system impairment tends to be more pronounced when:

  • Exercise is continuous, prolonged (longer than 90 minutes) and moderate to high in intensity
  • There is no alternating between hard and easy days
  • There isn't enough time for rest and recovery
  • There are too many competitions

Rest and recovery are key

Training too hard without allowing for sufficient recovery time can contribute to illness and decreased performance. To ensure a successful training program and to perform at one's best, it's critical to build in appropriate time for rest and recovery — including relaxing and getting enough sleep (strive for eight hours every night).

It's also important to follow basic hygiene rules, such as frequently washing hands and not sharing personal items with other teammates. Even when athletes take precautions, however, they can still get sick. Scientists debate whether upper respiratory symptoms are always due to either viral or bacterial infections. Symptoms can also be explained by local inflammation in the nose or throat or as a result of reactivation of a previous infection.

Nov. 12, 2016