This is an excerpt from Nutrition for Sport, Exercise, and Health 2nd Edition With HKPropel Access by Marie Spano,Laura Kruskall & D. Travis Thomas.
Zinc is essential for immune system functioning. This mineral promotes wound healing and helps maintain skin integrity, one of the first lines of defense against pathogens. Zinc is essential for the metabolism of carbohydrates, proteins, and fats, gene expression, red blood cell functioning, protein synthesis, glucose use, hormone metabolism, normal taste and smell, and growth and development. Zinc is not stored in the body and thus must be consumed daily (180).
Some, though not all, studies show that zinc gluconate lozenges taken within 24 hours of the onset of cold symptoms may be helpful for decreasing the duration and severity of the symptoms (181-185). Other studies have used different forms of zinc, so it remains unclear what dose, formulation, and duration of zinc consumption is best (185, 186). When using a zinc lozenge or other zinc supplement, consume the zinc according to package directions for a few days at the early onset of symptoms. Do not take a zinc supplement long term, because this can lead to adverse side effects, including suppressed immune system functioning (140, 187). Excess zinc may decrease magnesium balance and copper absorption, so monitor the number of zinc lozenges you take, especially when combined with a multivitamin mineral supplement with over 100%DV for zinc (188, 189).
Sources of Zinc
Many foods are good or excellent sources of zinc. Oysters are among the highest sources, containing nearly 500 percent of the DV for zinc in just 3 ounces. Red meat is another excellent source, and poultry, fish, baked beans, and cashews are good sources. Diets high in protein provide substantial amounts of zinc (11).
Inadequate and Excess Zinc Intake
National survey data suggest that few people consume below the EAR for zinc (36), but several studies in athletes show low dietary intake or low zinc status. This research shows that various athletes are not consuming enough zinc through their diet, including a small group of competitive male swimmers in Brazil, male and female adventure race athletes, male and female U.S. national figure skaters, trained female cyclists, and female high school gymnasts (91, 116, 190-192). Vegetarians, athletes consuming very high-carbohydrate, low-fat diets, and those who don’t meet their daily calorie needs are more likely to fall short of recommended intake levels for zinc (186, 191, 193). Because of lower overall energy intake, female athletes are less likely than male athletes to meet their zinc needs (194, 195). See figure 7.12 for sample dietary patterns (vegetarian and nonvegetarian) that meet most micronutrient needs including those for zinc.
Although zinc deficiency is considered rare (4), inadequate zinc intake can impair energy production and measures of athletic performance (196, 197). The primary symptom of zinc deficiency is growth retardation. Additional symptoms include hair loss, diarrhea, eye and skin lesions, poor appetite, and delayed sexual maturation (4). Zinc deficiency can also delay wound healing, suppress immune system functioning, and cause weight loss (187, 195). Excess supplemental zinc intake over a long period can suppress immune system functioning, lower HDL, and inhibit copper absorption, potentially leading to copper deficiency (140).
Do You Know?
Chelated means attached to another compound. Chelated minerals are often attached to an amino acid. In some, though not necessarily all, instances, chelation improves absorption.
Zinc and Exercise
Zinc is part of the red blood cell enzyme carbonic anhydrase, which picks up carbon dioxide for the lungs to exhale, an important step for chemical balance in muscle cells. Zinc deficiency leads to a decline in carbonic anhydrase activity, a reduction in peak oxygen uptake and peak carbon dioxide output, and a decrease in respiratory exchange ratio, suggesting that the body had insufficient oxygen to use carbohydrates efficiently (197).
Low zinc levels lead to a decline in muscle strength and power output. Marginal zinc deficiency is associated with low levels of testosterone, thyroid hormones, and IGF-1, a hormone that promotes muscle growth and metabolism (196, 198). Correction of zinc deficiency with zinc or iron and zinc improves red blood cell functioning in those with anemia (199, 200). Although zinc has an important role in athletic performance, at this time there is little quality evidence that zinc can improve athletic performance (201).