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Low dietary zinc decreases erythrocyte carbonic anhydrase activities and impairs cardiorespiratory function in men during exercise^1,2,3,4

¹ From the US Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND

Background: The role of zinc in promoting physiologic function during exercise is not well understood. Although some zinc-containing enzymes are postulated to regulate energy expenditure, data are limited on the effect of restricted dietary zinc on metabolic responses during exercise.

Objective: This study determined the effects of low zinc intake on carbonic anhydrase activity in red blood cells (RBCs) and cardiorespiratory function during exercise.

Design: In this double-blind, randomized crossover study, 14 men aged 20–31 y were fed low-zinc and supplemented (3.8 and 18.7 mg/d) diets made up of Western foods for 9-wk periods with a 6-wk washout. Peak work capacity, determined by using a cycle ergometer and a graded, progressive protocol, and a prolonged submaximal test (70% peak intensity for 45 min) were administered during the second and ninth weeks of each diet period.

Results: Dietary zinc did not affect hemoglobin or hematocrit. Low dietary zinc resulted in lower (P < 0.05) serum and erythrocyte zinc concentrations, zinc retention, and total carbonic anhydrase and isoform activities in RBCs. Peak oxygen uptake, carbon dioxide output, and respiratory exchange ratio were lower (P < 0.05), and ventilatory equivalents for metabolic responses during exercise were greater (P < 0.05), with low than with supplemental zinc intake. Similar functional responses were observed during prolonged, submaximal exercise.

Conclusion: These findings indicate that low dietary zinc is associated with significant reductions in zinc status, including RBC carbonic anhydrase activities, and impaired metabolic responses during exercise.

Key Words: Zinc depletion • erythrocyte carbonic anhydrase • cardiorespiratory function • humans