Where should you spend your time and money?

Athletes undertaking regular strenuous exercise walk a knife-edge between extreme physical well-being and impaired immune function. Research indicates that athletes are at increased risk of upper respiratory tract infection during periods of heavy exercise and for 1-2 weeks following race events (Nieman 1990). The cause of this increased risk is most likely due to the immunosuppressive actions of stress hormones such as adrenaline and cortisol (Gleeson et al. 2004).

Given this, what strategies can athletes undertake to minimise their risk of ill health while training and competing?

Firstly, it is important to realise that immune function suppression in athletes is multi-factorial – a fact that many athletes overlook.  David Nieman, a world leading researcher of immune function in athletes states that “It makes sense that Upper Respiratory Tract Infection risk may be increased when the endurance athlete goes through repeated cycles of unusually heavy exertion, has been exposed to novel pathogens, and experienced other stressors to the immune system including lack of sleep, severe mental stress, malnutrition, or weight loss” (Nieman 2003). Athletes often neglect many of these factors following exercise and focus their attention on the well-publicised virtues of nutritional supplements that claim to boost immune function.

In a study investigating the use of sports foods and dietary supplements in 77 elite Australian swimmers, researchers found that 99% of athletes reported using these products, with the most popular dietary supplements used being vitamin and mineral supplements (94% of the group) and herbal preparations (64% of the group) (Baylis et al. 2001).  Despite the heavy reliance by athletes on nutritional supplements, currently there is a lack of evidence to support high doses of anti-oxidant vitamins, glutamine supplementation or echinacea extracts in preventing exercise-induced immune suppression and protection from infection (Gleeson et al. 2004).

An adequate dietary intake of protein and specific micronutrients including vitamins A, C, E, B6 and B12 along with iron, zinc, copper and selenium are all critical factors for the maintenance of optimum immune function.  The “million dollar” question for athletes is whether or not supplemental forms or megadoses of these nutrients are beneficial.

There is a growing list of research papers that report indifferent results on the effects of nutritional supplements on the acute immune response to exercise.  Antioxidants (i.e. vitamins C and E) and glutamine have received considerable attention, but the data thus far does not support their role in negating immune function changes after heavy exercise (Gleeson et al. 2004).

Current opinion is that athletes should invest in nutrient-rich foods and fluids that provide sufficient energy and a wide range of vitamins, minerals and other important chemicals, such as phytochemicals, found naturally in foods. Furthermore, forward planning and an organised daily food intake are necessary to ensure appropriate foods are consumed in order to meet the nutrition goals for training and competition.  In real life, many athletes fail to spend the necessary time and effort to eat cleverly over the day to promote an optimal workout and recovery.

Recent research suggests that a sufficient carbohydrate intake in the days preceding strenuous exercise acts as an effective countermeasure to the suppression in immune function that occurs following exercise.  In a recent review, Michael Gleeson and colleagues (2004) state that “an athlete exercising in a carbohydrate-depleted state experiences larger increases in circulating stress hormones” than the athlete who is well-fuelled for exercise.  They go on to say that “consuming carbohydrate during exercise attenuates rises in stress hormones” and “appears to limit the degree of exercise-induced immunosuppression”. Recently a team of researchers from Birmingham and Loughborough Universities demonstrated that consuming 30-60 g of carbohydrate per hour during 2½ hours of strenuous cycling prevented a decrease in markers critical to anti-viral defence (Lancaster et al. 2003).

Although further research is warranted in this area, matching carbohydrate intake with daily fuel needs may protect immune function following prolonged strenuous exercise.

References:

• Baylis, A., Cameron-Smith, D., and L.M., Burke. Inadvertent doping through supplement use by athletes: Assessment and management of the risk in Australia. International Journal of Sports Nutrition and Exercise Metabolism. V11(3):365-383, 2001.
• Gleeson, M., Nieman, D., Pedersen, B.K. Exercise, nutrition and immune function. Journal of Sports Sciences. 22:115-125, 2004.
• Lancaster, G.I., Khan, Q., Drysdale, P., Jeukendrup, A.E., Drayson, M.T., and M. Gleeson. Effect of feeding different amounts of carbohydrate during prolonged exercise on human T-lymphocyte intracellular cytokine production. Journal of Physiology, 548P: O98, 2003.
• Nieman, D.C., Johansen, L.M., Lee, J.W., and Arabatzis, K. Infectious episodes in runners before and after the Los Angeles Marathon. Journal of Sports Medicine and Physical Fitness. 30:316-328, 1990.
• Nieman, D. Potential nutritional countermeasures to exercise–induced immunosuppression.  European College Sports Science, Salzburg, Austria, 2003.
• Pyne, D.B., Gleeson, M., McDonald, W.A., Clancy, R.L., Perry, C. Jr., Fricker, P.A. Training strategies to maintain immunocompetence in athletes. International Journal of Sports Medicine. 21 Suppl 1:S51-60, 2000.