The theory that athletes need to take zinc supplements to protect their immune systems during periods of heavy training has been cast into doubt by a new study from Australia and New Zealand.

Zinc is vital to healthy immune function, and previous studies have shown that people with severe zinc deficiency are prone to a range of disorders linked with compromised immunity, including an increased incidence of infection. It has been suggested that athletes may have inadequate dietary intakes of zinc (found more in protein than in carbohydrate foods) and that regular intense exercise may reduce blood zinc concentrations further, so posing a threat to health.

The researchers put this hypothesis to the test in a study of 10 male runners, who increased their normal training volume of long slow distance running by 16% over four weeks, then reduced it to recovery levels for a further two weeks. Blood samples taken from the athletes before and after the four weeks’ intensified training, and again after the two weeks’ recovery, were analysed for plasma zinc concentration and immune system markers and compared with samples taken from a group of seven sedentary male ‘controls’.

Key findings were as follows:

• The athletes generally had lower plasma zinc concentrations than the non-athletes both before and during the four weeks of intensified training, but these remained within the clinically normal range and were unchanged in response to the moderate increase in training volume;
• Although cell counts for some lymphocytes (white blood cells involved in immunity) were lower in the athletes than the controls, they were unaffected by training and lymphocyte responsiveness was similar or higher in the athletes than the controls. Thus plasma zinc concentrations generally correlated poorly with the immune parameters under investigation;
• Five out of 10 athletes experienced varying degrees of illness during the study, compared with two out of seven controls.

The researchers conclude that their results do not support the use of zinc supplements among well-trained athletes during a period of moderately increased training volume.

Int J Sports Med 2003;24:212-216