There have been many other studies which have taken a look at the effect of exercise on zinc status. There are several rationales proposed for the cause of the hypozincemia seen resulting from training in athletes. These include 1.) the expanasion of plasma volume 2.) increase zinc excretion (urinary and sweat) 3.) redistribution of zinc. Plasma zinc levels have been seen to decrease at a rate of from 12-33% during physical training, and only up to a 12% loss can be attributed to increase in plasma volume. Studies have found that urinary zinc loss increases by 10-45% after moderate exercise, and is higher in trained athletes than sedentary. Sweat zinc losses have been seen in males (0.65mg/hour) and females (0.4mg/hr) after one hour of moderate intensity exercise. Normal dermal losses of zinc have been rated as 0.76mg/day. It has also been shown that exercise will cause zinc to be redistributed to counteract some of the physiological impact of exercise.
Some goes to the liver, forming enzymes and some to the erythrocytes. In particular, exercise has been shown to increase zinc erythrocyte levels in the endurance athlete.Plasma zinc increases and erythrocyte zinc decrease following high intensity exercise. Overall, exercise results in the loss of zinc, and exercise done on a regular basis can lead to a negative compromise in zinc status. It is of note that a study in 2006 (Kilic M, et al., Neuro Endocrinol Lett 2006;27(1-2): 247-252) examined the effect of exhaustive exercise in elite athletes, and its effect on thyroid and testosterone levels. The study determined that exhaustive exercise led to a significant inhibition of both thyroid and testosterone concentrations. Further, the researchers found that a 4 week course of oral zinc supplementation prevented this inhibition, and they concluded that physiological doses of zinc may benefit athletic performance. The relationship here could be a real key.
Research findings on zinc and its interplay with exercise and athletic performance will continue to bring in new and exciting findings. The physiological and biochemical changes related to zinc metabolism and exercise are complex, and the effect of exercise on any one compartmental level or enzyme level of zinc has been seen to vary by the type of exercise (aerobic or anaerobic), duration of exercise, intensity of exercise, as well as the repetition of certain exercise over long periods of time. Given the function of zinc in exercise, the zinc status of an individual prior to the start of exercise is an important element. As you will see in Table 1, the starting zinc status for the US population is low. Knowing that over the long haul, exercise programs demand zinc, and that marginal deficiencies in zinc will have a negative impact on the immune system and health, a dietary program to insure proper zinc intake is important to athletic success.