Monday, November 17, 2008

Training, Colds, Flu and Respiratory Infections

As the soccer season moves into the cold and flu season, it becomes more and more important for players to take precaution against illness. The months of November through February can be a time when practices become more intense as players ready themselves for end of the year tournaments. In addition, the stress of school work, college recruiting and the holiday season increases during this period. The combined effects of physiological, psychological and emotional stress can compromise the immune system and leave players more susceptible to colds, flu and upper respiratory infections. There are a few things that can be done to reduce the risk of developing these illnesses. By paying attention to diet and managing both physical and psychological stressors, players may be able to avoid developing sickness.

Most of the research on exercise and immune function show that moderate training boosts the immune system and provides some degree of prevention from colds and flu. However, periods of heavy or intense training can actually make athletes more susceptible to these ailments. Researchers describe the relationship between training intensity and risk of illness as a “J” curve (see Figure, click to enlarge). That is, as individuals increase their training level from sedentary (untrained) to moderate, the risk of illness declines. As athletes increase their training intensity and engage in unusually heavy workloads, their risk of illness increases, often above that of a sedentary individual. Most researchers also agree that the risk of developing colds and flu parallel changes in the athletes’ immune system. That is, intense periods of training seems to suppress the immune system which leaves the athlete vulnerable to illness. This is particularly problematic during the winter months and cold and flu season.

Researchers also talk of an “open window” period following heavy exercise (see Figure, click to enlarge). In the hours following an intense training session, the immune system may be suppressed. During this time, viruses and bacteria may be able to gain a foothold in the athlete. This open window period makes him or her particularly susceptible to developing illnesses. Interestingly, this is also a period where athletes may be in close quarters with other athletes (warm, damp locker rooms, long car rides home from training, etc) or sharing items such as water bottles, towels or training gear.

There are several other factors that might depress an athlete’s immune system and make him or her susceptible to illness. Periods of intense training are usually times of great psychological stress and lack of sleep. As the competitive season wears on, the pressure of performing well often increases and the academic demands of school is typically greater that at other times of the season. This leads to increased mental and emotional stress as well as physical fatigue, all of which are detrimental to immune system function.

Can nutritional supplements help boost the immune system? The answer to this question is yes and no. Very few supplements will actually “boost” the immune system. Antioxidants are routinely advertised as boosting the immune system. Supplement companies boast the benefits of vitamins C and E as well as minerals such as zinc and magnesium in fighting off colds and flu. Unfortunately, there is little scientific evidence that either of these helps counter immune suppression of oxidative stress during periods of heavy training. As such, most researcher do not recommend vitamin supplement for the prevention of illness. The amounts of vitamins and minerals included in a well balanced diet are sufficient. Only if an athlete’s diet is deficient in vitamins and minerals, might a daily multivitamin be beneficial.

Likewise, glutamine supplements are also advertised as being beneficial to the athlete. Heavy exercise has been shown to lower plasma glutamine levels. However, these changes are not great enough to compromise the immune system. In addition, several well designed studies show that glutamine supplements taken during training had no effect on the immune system. Thus, it is unlikely that glutamine supplements will lower ones risk of illness.

The good news is that there are some proper dietary habits can help prevent immunosuppression during times of compromise (heavy training, stress). Carbohydrate supplements taken during training can blunt the “open window” period that occurs in the hours after an intense training session. Studies have shown that drinking a carbohydrate beverage during training can lower the levels of stress hormones and lead to smaller adverse changes in the immune system. It’s not entirely clear if this will actually help athlete avoid sickness, but most of the research suggests that their risk may be lowered.

There are also a few nutritional ingredients that may prove beneficial in countering immunosuppression in athletes. These include curcumin and quercetin. Curcumin is found in the spice tumeric and curry powder. It seems to modulate the immune system. Studies in laboratory animals show promising results with exercise. Quercetin is a polyphenol found in foods such as onions, apples, blueberries and broccoli. Preliminary research on both animals and humans show positive effects on immune function and oxidative stress associate with exercise. At this time, no firm conclusions can be drawn from preliminary animal and human studies. However, these compounds may yet prove beneficial. Interstingly, a diet high in a variety of fruits and vegetables is likely to also be high in quercetin.

So, what conclusions can be draw from this research? There are a few dietary strategies that can be made regarding exercise, stress and immune function. A varied, healthy diet is critical to maintaining proper immune function. Diets and are rich in protein, carbohydrates and vitamins are very important in supporting immune system defense against infection and illness. A multivitamin may provide some protection if the athlete’s diet is less than optimal. It is unlikely however, that vitamin / mineral supplements will boost the immune system above normal levels.

Players should also develop hygiene strategies that can help him or her avoid colds and flu. Avoid sharing equipment that can easily transmit viruses and bacteria. This includes water bottles, equipment, clothing and towels. Also avoid close contact with anyone who shows signs of sickness. Athletes who find themselves developing a cold or flu should be aware that they are highly contagious for passing their illness on to others.

A third strategy is to plan the weekly academic schedule ahead of time. Planning academic studies in advance will help you avoid much of the stress associated with school. In addition, following a study plan will almost certainly help players avoid late night study session and help them get plenty of sleep.

As for coaches, they should closely monitor their athletes. Realize that this time of the year when players are susceptible to illnesses and that a sick athlete is of little help to the team. If the team or individual players show signs of physical of psychological stress (easily fatigued, lethargic, etc), adjust the intensity of practice accordingly. Also emphasize the importance of proper diet, sleep and academic planning. Also, watch that players are not sharing water bottles or training gear. Above all, remember that a sick athlete is of little use to the team.

Practicing these recommendations is no guarantee that players will avoid colds, flu and upper respiratory infections. However, they will go a long way towards lowering their risk.

References:

Nieman DC (2008) Immunonutrition support for athletes, Nutrition Reviews, 66:310-320.

Gleeson M (2007) Immune function in sport and exercise. Journal of Aplied Physiology, 103:693-699.

Nieman DC, Bishop NC (2006) Nutritional strategies to counter stress to the immune system in athletes, with special reference to football. Journal of Sports Sciences, 24:763-772.