Posted: October 10, 2006

Science of Sport: Performance potion – The Zinc effect

This article originally appeared in the sports science newsletter, Peak Performance When athletes try to organize a balanced diet, they think about good carbs and the correct amounts of protein, but who really cares about zinc levels? Only in a recent study has it been proved this could be a mistake. Fourteen young healthy men were randomly divided into two groups, both fed a typical Western diet for a period of nine weeks. However, one group’s diet contained low-zinc foods, providing a daily intake of around 3.8mg per day, while the other included high-zinc foods, providing a daily intake of around 18.7mg per day. After a six-week washout period (during which both groups returned to their normal eating habits), the protocol was reversed for another nine weeks – ie the low-zinc group followed the high-zinc diet, and vice-versa. At the beginning and end of the two nine-week dietary regimes, peak work capacity was determined by means of a graded, progressive cycling test and a prolonged sub-maximal test (70% VO2max for 45 minutes). The researchers also checked on blood levels of zinc and iron because very high levels of zinc intake can interfere with iron absorption, which could in turn impair oxygen transport and aerobic capacity. Analysis of the results showed the men used less oxygen, produced less carbon dioxide and breathed more strenuously during exercise on the low-zinc diet by comparison with the high-zinc diet. These findings provide an explanation for previous findings of decreased muscle strength and endurance in adolescents and adults with low-zinc status. And the researchers conclude that low-zinc diets cause impaired peak aerobic power, aerobic efficiency and ventilatory efficiency. Given that many ‘Western’ diets are estimated to contain significantly less than the recommended daily intake of zinc (15mg per day), it seems prudent for anyone engaged in physical activity, training or sport to review their diet to make sure they are consuming sufficient quantities of this vital nutrient. American Journal Of Clinical Nutrition 2005; 81:1045-1051

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