Friday, June 1, 2007

Keeping the Bugs at Bay during the Winter Season

Keeping the Bugs at Bay during the Winter Season
Dr David Nieman
From Coaching Australia. Vol. 9. No 1. August 2005
The relationship between exercise and the immune system is of great importance for coaches and their athletes during the winter season, when illness and infection can compromise an athlete in training and competition.

The ‘open window’ theory
It has been suggested that bouts of heavy, prolonged exercise can lead to a temporary but clinically significant reduction in an athlete’s immune function. During this so-called ‘open window’ of altered immunity, which may last between three and 72 hours depending on the immune measure, viruses and bacteria may be able to gain a foothold, increasing the risk of infection. Parts of the immune system that may change after prolonged, heavy exertion include:

decrease in natural killer-cell activity — the ability to kill infected cells or cancer cells decrease in nasal and salivary Immunoglobulin A concentration — an antibody that combines with protein in saliva and tears to defend the body from invading germs

high blood levels of the hormone cortisol cause high blood levels of neutrophils and low levels of lymphocytes — two different types of white blood cells

decrease in nasal mucociliary clearance — sweeping movement of small hair-like structures in the nose

increase in plasma concentrations of pro and anti-inflammatory immune cells known as cytokines.

Taken together, these changes suggest that the immune system is temporarily suppressed and stressed following prolonged endurance exercise. It has been suggested that the immune system reacts to the inflammation caused by heavy exertion, diverting resources that normally protect against infection, particularly upper respiratory tract infection.

Thus it makes sense, but still remains unproven, that upper respiratory tract infection risk is probably increased when an athlete goes through repeated cycles of heavy exertion, has been exposed to viruses and bacteria that cause infections, and has experienced other stressors to the immune system, including lack of sleep, severe mental stress, poor nutrition or weight loss.

Role of nutritional supplements in reducing exercise-induced changes in immunity
Although endurance athletes may be at increased risk of upper respiratory tract infections during heavy training cycles, they still need to exercise intensively to compete successfully. Therefore, one solution could be taking nutrient supplements that have the potential to boost immune function. The influence of carbohydrate, vitamin C and glutamine on the immune response to intense and prolonged exercise has been investigated with varying results.

The most impressive results have been reported in carbohydrate supplementation studies. Research has established that blood glucose concentrations are linked to the body’s hormonal system, including the stress hormones. This, in turn, is linked to the body’s immune system. By keeping the blood glucose levels up, stress hormones are reduced and immune system function is better maintained than when just water is ingested.

Research shows that athletes ingesting carbohydrate beverages before, during and after prolonged and intensive exercise should experience lowered physiologic stress.

This model suggests that carbohydrate supplementation during prolonged and intensive exercise maintains or elevates blood glucose concentrations, reduces the normal rise in stress hormones, and thereby counters negative immune changes.

Vitamin C
Several studies of South African ultra-marathon runners have shown a link between vitamin C supplementation (about 600 mg/day for three weeks) and fewer reports of upper respiratory tract infection. While findings suggest that vitamin C supplementation may be beneficial during and after strenuous physical activity, the data does not prove that supplementation with vitamin C is also beneficial during moderate training.

Glutamine, a non-essential amino acid (building block of protein), has attracted much attention from investigators.
Lower levels of glutamine result in reduced immune function, and reduced blood glutamine levels have been observed after prolonged exercise. It has been suggested that glutamine supplementation may overcome the problems of overtraining, or the impaired immune function suffered by athletes involved in heavy training. However, most studies have not favoured such a relationship.

There is growing evidence that prolonged intensive exercise is associated with reduced immune function and an increased susceptibility to opportunistic infections, particularly upper respiratory tract infections. Exercise-induced increases in stress hormones may be responsible. Attempts have been made to prevent these negative changes through nutritional means, with carbohydrate supplementation via a sports drink offering the most promising results so far.

Practical tips for coaches
Athletes are urged to eat a well balanced diet, minimise other life stresses, avoid overtraining, get adequate sleep and space vigorous workouts as far apart as possible. New research suggests that drinking carbohydrate beverages before, during, and after prolonged and intensive sessions can lessen the stress on the immune system. The immune system appears to be suppressed during periods of low energy intake and weight reduction, so athletes should lose weight slowly during non-competitive phases. Cold viruses are spread by personal contact and breathing the air near sick people. Athletes should avoid being around sick people before and after important events. If the athlete is competing during winter, a flu shot may be recommended, particularly for those at high risk of infection.

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