Author
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Lukaski, Henry |
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Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/10/2004 Publication Date: 5/1/2005 Citation: Lukaski, H.C. 2005. Low dietary zinc decreases erythrocyte carbonic anhydrase activities and impairs cardiorespiratory function in men during exercise. American Journal of Clinical Nutrition. 81:1045-1051. Interpretive Summary: With the growing emphasis by public health groups to increase physical activity and select healthful diets to reduce risk of chronic diseases, the public seeks information about the roles that specific nutrients play in health promotion. Zinc is a nutrient that has attracted public attention because half of the US population consumes less than the average recommended daily zinc intake. Also, zinc intakes of some groups of physically active people also are less than recommendations. To address the role of zinc in supporting energy use during exercise, 14 men were studied. They were randomly assigned and fed diets consisting of Western foods for a 9 week period followed by a 6 week period when they selected any foods then another 9 week period. Diets were low and high zinc (3.8 and 18.8 mg per day). The men used less oxygen, produced less carbon dioxide, and breathed more strenuously during exercise when they consumed the low compared to the high dietary zinc. Blood biochemical indicators of zinc status, serum and red blood cell zinc concentrations, decreased when dietary zinc was low. Importantly, the activity of carbonic anhydrase, a zinc-containing enzyme, in red blood cells decreased with restricted dietary zinc. This enzyme plays a key role in facilitating removal of carbon dioxide from cells. The finding of reduced carbonic anhydrase activity is consistent with the reduced carbon dioxide elimination and increased ventilation during exercise. This finding provides the first observation of altered biological function during exercise when dietary zinc is low, and gives the first explanation of previous results of decreased muscle strength and endurance in adolescents and adults with low zinc status. These findings will be useful to researchers who seek to determine the role of zinc in promoting human health and optimal function. Technical Abstract: The role of micronutrients such as zinc in promoting physiological function during exercise is not well defined. Although some zinc-containing enzymes are postulated to participate in regulation of energy expenditure, data are limited on the effect of dietary zinc on metabolic responses during exercise. Dietary zinc may impact physiological function during periods of increased energy use by influencing the activity of carbonic anhydrase, a zinc-containing enzyme, in red blood cells. Fourteen men, aged 20-31 y, were randomly assigned and fed diets made of conventional Western foods for 9-wk periods with a 6-wk washout in a double-blind, cross-over study with low and supplemental zinc (3.8 and 18.7 mg/d) diets. Peak work capacity was determined by using a graded, progressive ergocycle protocol at the start and end of each diet period; a prolonged submaximal test (70% peak intensity for 45 min) also was administered. Dietary zinc did not affect hemoglobin or hematocrit. Low dietary zinc resulted in decreases (p<0.05) in serum and erythrocyte zinc concentrations, zinc retention, and total carbonic anhydrase and isoform activities in red blood cells. Peak oxygen uptake, carbon dioxide output and respiratory exchange ratio decreased (p<0.05) whereas ventilatory equivalents for metabolic responses during exercise increased (p<0.05) with low Zn intake. Similar functional responses were observed during submaximal exercise. These findings indicate that low dietary zinc resulted in significant decreases in erythrocyte carbonic anhydrase activities and is associated with impaired metabolic response during exercise. |
