The red blood cell enzyme carbonic anhydrase contains a zinc cofactor. A diet deficient in zinc does not reduce the number of red blood cells, but it impairs respiratory function by reducing output. Explain why.

Low dietary zinc decreases erythrocyte carbonic anhydrase activities and impairs cardiorespiratory function in men during exercise

Abstract

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.

Explanation:

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