It is known that strenuous exercise can result in marked changes in zinc metabolism. The variations in plasma zinc levels can be related to the intensity of the exercise [Cordova A; Alvarez-Mon M; Neurosci Biobehav Rev. 1995; 19(3)]. Cordova and Alvarez state that it is clear that there are short term effects of exercise on zinc metabolism, and that a constant high level of exercise will give rise to other long term effects on zinc metabolism. Long term endurance training gives rise to lowered resting serum zinc levels in both males and females as compared to sedentary controls. Severe zinc deficiency can affect muscle function, since zinc is required for the activity of several enzymes in energy metabolism in muscle. A low muscle zinc will result in a reduction of endurance capacity. Several studies have shown that athletes involved in anaerobic exercise (short powerful movements, as in weight training, judo) exhibit higher plasma zinc levels than those who are involved in aerobic exercises like cycling or jogging. The following two abstracts are included here, due to their classic findings on zinc and exercise.
Serum zinc was measured four times (October, January, March and May) in six young male athletes during a nine-month sporting season in relation to eleven other parameters. A significant decrease in serum zinc was observed after five months of intensive training (all values remaining in the normal range). This cannot be explained by changes in dietary habits, plasma protein concen trations, hormonal changes nor by the existence of minor infectious or inflammatory pathologies. The dietary intakes seemed adequate. These results support the hypothesis that zinc status may be slightly altered in the high-level athlete.
The purpose of this research was to determine the effects of daily physical training on serum and sweat zinc concentrations in professional sportsmen between October and December, during the competing season. Twelve volleyball players and another 12 control subjects have participated in this study. Tests were made in October and December which consisted of a progressive bicycle ergometer test (increasing 30 W every 3 min to reach maximum tolerated power). Blood samples were obtained at rest and immediately after exercise. Total serum zinc increased significantly after maximal exercise in both sportsmen and control subjects. In athletes, the change after exercise was significantly higher in December than in October. The percentage of ultrafiltrable zinc (ZnUf) in October was similar in sportsmen and in controls. In December, however, after exercise, the percentage of ZnUf was higher in athletes. With respect to sweat zinc, it was in the same range both in controls and in sportsmen in October. In December, however, sweat zinc was significantly higher in athletes as compared with the situation in October and with respect to the control group. In October, the zinc concentration of urine was similar for sportsmen and controls. In December, the sportsmen showed an increase in urinary zinc excretion with respect to control subjects. Cortisol in athletes increased significantly after exercise in December. In conclusion, a daily and maintained practice of exercise is probably responsible for an alteration of zinc metabolism. The results suggest that ZnUf control, zinc supplementation and/or stress control appear to be indicated in athletes to prevent the diminution of active ZnUf. In our practical opinion we think that alterations in zinc metabolism with increases in zinc excretion and stress levels lead to a situation of latent fatigue with a decreased endurance.