The effects of zinc depletion on peak force and total work of knee and shoulder extensor and flexor muscles

Benefits of a plant-based diet and considerations for the athlete

Individuals may opt to follow a plant-based diet for a variety of reasons, such as religious practices, health benefits or concerns for animal or environmental welfare. Such diets offer a broad spectrum of health benefits including aiding in the prevention and management of chronic diseases. In addition to health benefits, a plant-based diet may provide performance-enhancing effects for various types of exercise due to high carbohydrate levels and the high concentration of antioxidants and phytochemicals found in a plant-based diet. However, some plant-based foods also contain anti-nutrional factors, such as phytate and tannins, which decrease the bioavailability of key nutrients, such as iron, zinc, and protein. Thus, plant-based diets must be carefully planned to ensure adequate intake and absorption of energy and all essential nutrients. The current narrative review summarizes the current state of the research concerning the implications of a plant-based diet for health and exercise performance. It also outlines strategies to enhance the bioavailability of nutrients, sources of hard-to-get nutrients, and sport supplements that could interest plant-based athletes.

Malnutrition in Orthopaedic Sports Medicine: A Review of the Current Literature

CONTEXT

Malnutrition is well-studied in various aspects of the orthopaedic literature, most commonly in relation to arthroplasty, spine surgery, and trauma. However, the management of nutritional deficiencies is commonly overlooked among orthopaedic sports medicine providers. The purpose of this article is to analyze the available sports medicine literature to review the associations between malnutrition and the management of orthopaedic sports medicine patients from a treatment and performance standpoint.

EVIDENCE ACQUISITION

PubMed was searched for relevant articles published from 1979 to 2019.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 4.

RESULTS

Few studies exist on the implications of macronutrient deficiencies specific to orthopaedic sports medicine procedures. Interestingly, micronutrient disorders-namely, hypovitaminosis D and iron deficiency-have been well studied and may lead to worse postoperative outcomes, injury rates, and athletic performance. Nutritional supplementation to correct such deficiencies has been shown to mitigate these effects, though further study is required.

CONCLUSION

Nutritional deficiencies are highly prevalent in orthopaedic sports medicine patients, and practitioners should be aware of their potential effects on treatment and performance outcomes. Management of such deficiencies and their effect on surgical patients remain an area of potential future research. Future studies are warranted in order to explore the potential therapeutic role of nutritional supplementation to prevent complications after common orthopaedic sports medicine procedures, improve athletic performance, and reduce injury rates.

Zinc at the crossroads of exercise and proteostasis

Zinc is an essential element for all forms of life, and one in every ten human proteins is a zinc protein. Zinc has catalytic, structural and signalling functions and its correct homeostasis affects many cellular processes. Zinc deficiency leads to detrimental consequences, especially in tissues with high demand such as skeletal muscle. Zinc cellular homeostasis is tightly regulated by different transport and buffer protein systems. Specifically, in skeletal muscle, zinc has been found to affect myogenesis and muscle regeneration due to its effects on muscle cell activation, proliferation and differentiation. In relation to skeletal muscle, exercise has been shown to modulate zinc serum and urinary levels and could directly affect cellular zinc transport. The oxidative stress induced by exercise may provide the basis for the mild zinc deficiency observed in athletes and could have severe consequences on health and sport performance. Proteostasis is induced during exercise and zinc plays an essential role in several of the associated pathways.

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Zinc deficiency could be a crucial issue in sport performance for athletes.

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Exercise could modulate zinc serum and cellular homeostasis.

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Zinc is part of proteostatic systems critical during exercise.

Iron, Zinc, and Physical Performance

Iron and zinc are nutritionally essential trace elements that function through incorporation into proteins and enzymes; many of these proteins and enzymes affect physical performance. Poor iron status (iron deficiency and iron deficiency anemia) is prevalent in both developed and developing nations. Zinc deficiency has been reported in clinical and population studies, although the incidence is difficult to quantify due to the lack of a reliable zinc status indicator. The objective of this manuscript is to review the relationship between iron and zinc status and physical performance. In sum, numerous reports indicate diminished physical performance in individuals with poor iron and/or zinc status, whereas, in individuals with adequate status, evidence supporting a beneficial role of iron or zinc at levels beyond the recommended dietary allowance for optimizing physical performance is lacking.

Supplements with purported effects on muscle mass and strength

PURPOSE

Several supplements are purported to promote muscle hypertrophy and strength gains in healthy subjects, or to prevent muscle wasting in atrophying situations (e.g., ageing or disuse periods). However, their effectiveness remains unclear.

METHODS

This review summarizes the available evidence on the beneficial impacts of several popular supplements on muscle mass or strength.

RESULTS

Among the supplements tested, nitrate and caffeine returned sufficient evidence supporting their acute beneficial effects on muscle strength, whereas the long-term consumption of creatine, protein and polyunsaturated fatty acids seems to consistently increase or preserve muscle mass and strength (evidence level A). On the other hand, mixed or unclear evidence was found for several popular supplements including branched-chain amino acids, adenosine triphosphate, citrulline, β-Hydroxy-β-methylbutyrate, minerals, most vitamins, phosphatidic acid or arginine (evidence level B), weak or scarce evidence was found for conjugated linoleic acid, glutamine, resveratrol, tribulus terrestris or ursolic acid (evidence level C), and no evidence was found for other supplements such as ornithine or α-ketoglutarate (evidence D). Of note, although most supplements appear to be safe when consumed at typical doses, some adverse events have been reported for some of them (e.g., caffeine, vitamins, α-ketoglutarate, tribulus terrestris, arginine) after large intakes, and there is insufficient evidence to determine the safety of many frequently used supplements (e.g., ornithine, conjugated linoleic acid, ursolic acid).

CONCLUSION

 In summary, despite their popularity, there is little evidence supporting the use of most supplements, and some of them have been even proven ineffective or potentially associated with adverse effects.

Influence of an Acute Exercise Until Exhaustion on Serum and Urinary Concentrations of Molybdenum, Selenium, and Zinc in Athletes

The aim of the present study was to determine changes occurring in serum and urine concentrations of essential trace elements with proven essentiality (molybdenum, selenium, and zinc) as a result of performing an acute physical activity until exhaustion in middle- and long-distance runners who live in the same area of Extremadura (Spain). Twenty-one Spanish national middle- and long-distance runners and 26 sedentary students of a similar age were recruited for the study. Both groups ran on a treadmill until exhaustion, starting at a speed of 10 and 8 km/h, respectively, and increasing the speed at 1 km/h every 400 m, without modifying the slope, always within the recommended parameters. Serum and urine samples were obtained from all subjects before and after the tests. Analysis of trace metals was performed by inductively coupled plasma mass spectrometry (ICP-MS). Resting serum and urinary concentrations between groups were compared using the Student t test, and the Wilcoxon test was used to analyze the trends of changes before and after the effort. The results showed that molybdenum concentrations were significantly higher in athletes than in controls (p < 0.01). Selenium (p < 0.05) and zinc (p < 0.01) concentrations were significantly lower in athletes than in controls. When we compared the serum concentrations before and after the test in the controls, only in the case of selenium (p = 0.006), a significant increase was observed after the test. However, this signification disappears with the corrections for hematocrit. Athletes' serum concentrations of Se (p = 0.004) and Zn (p = 0.005) lowered at the end of the test. Also, the results showed that there were no statistical urinary concentration (expressed in μg/g creatinine) changes in Mo and Se. Zn urinary concentration increased at the end of exercise (p = 0.018), since an incremental exercise to exhaustion in middle- and long-distance elite athletes produces a decrease in Se and Zn serum concentrations but Zn urinary concentration increased. In conclusion, athletes show higher serum concentrations of molybdenum and lower serum concentrations of selenium and zinc than sedentary subjects. Additionally, a treadmill test until exhaustion provokes a decrease in serum concentration of selenium and zinc and a higher excretion of urinary zinc. Serum concentrations of Se and Zn should be carried out in order to avoid any possible deficit cases and to establish the optimal supplementation.

Use of Serum Zinc Concentration as an Indicator of Population Zinc Status

Assessing the prevalence and severity of zinc deficiency in populations is critical to determine the need for and appropriate targeting of zinc intervention programs and to assess their effectiveness for improving the health and well-being of high-risk populations. However, there is very little information on the zinc status of populations worldwide due to the lack of consensus on appropriate biochemical indicators of zinc status. The objective of this review was to evaluate the use of serum zinc concentration as an indicator of population zinc status.

We have reviewed the response of serum zinc concentration to dietary zinc restriction and zinc supplementation. In addition, we completed pooled analyses of nine zinc intervention trials in young children to assess the relations between serum zinc concentration of individuals before treatment and their responses to zinc supplementation. Also, in updated combined analyses of previously published data, we investigated the relation between the mean initial serum zinc concentration of a study population and their mean growth responses to zinc supplementation in randomized intervention trials among children.

The results from depletion/repletion studies indicate that serum zinc concentrations respond appreciably to severe dietary zinc restriction, although there is considerable interindividual variation in these responses. There is also clear evidence that both individual and population mean serum zinc concentrations increase consistently during zinc supplementation, regardless of the initial level of serum zinc concentration. By contrast, an individual's serum zinc concentration does not reliably predict that person's response to zinc supplementation.

Serum zinc concentration can be considered a useful biomarker of a population's risk of zinc deficiency and response to zinc interventions, although it may not be a reliable indicator of individual zinc status.

Zinc: physiology, deficiency, and parenteral nutrition

The essential trace element zinc (Zn) has a large number of physiologic roles, in particular being required for growth and functioning of the immune system. Adaptive mechanisms enable the body to maintain normal total body Zn status over a wide range of intakes, but deficiency can occur because of reduced absorption or increased gastrointestinal losses. Deficiency impairs physiologic processes, leading to clinical consequences that include failure to thrive, skin rash, and impaired wound healing. Mild deficiency that is not clinically overt may still cause nonspecific consequences, such as susceptibility to infection and poor growth. The plasma Zn concentration has poor sensitivity and specificity as a test of deficiency. Consequently, diagnosis of deficiency requires a combination of clinical assessment and biochemical tests. Patients receiving parenteral nutrition (PN) are susceptible to Zn deficiency and its consequences. Nutrition support teams should have a strategy for assessing Zn status and optimizing this by appropriate supplementation. Nutrition guidelines recommend generous Zn provision from the start of PN. This review covers the physiology of Zn, the consequences of its deficiency, and the assessment of its status, before discussing its role in PN.

Marginal zinc deficiency negatively affects recovery from muscle injury in mice

The aim of the present study was to elucidate whether the recovery from muscle injury is impaired in marginal zinc deficiency. C57BL/6 male mice were fed a marginally zinc-deficient diet (MZD: 8 mg Zn/kg diet), a zinc-adequate diet (ZA: zinc 35 mg Zn/kg diet), and a zinc-high diet (ZH: 190 mg Zn/kg diet) for 4 weeks. Muscle injury was induced in the gastrocnemius muscles using cardiotoxin. The gastrocnemius muscles of these mice were harvested at 3, 5, 7, 10, 14, and 20 days after injury. We evaluated the regeneration of the skeletal muscle with hematoxylin and eosin staining and developmental myosin heavy-chain (dMHC: implicated in regeneration) immunostaining. The rate of dMHC-positive cells was significantly low in MZD mice compared with ZA mice at 3 days after cardiotoxin injection. The peak dMHC expression was found at 3 days after injection in ZA mice, 5 days in ZH mice, and 7 days in MZD mice. These results suggest that recovery from muscle injury might be partly impaired and delayed in MZD mice. Therefore, we strongly suggest the appropriate zinc intake to prevent the impairment of skeletal muscle regeneration.

Effect of zinc and selenium supplementation on serum testosterone and plasma lactate in cyclist after an exhaustive exercise bout

Zinc and selenium are essential minerals and have roles for more than 300 metabolic reactions in the body. The purpose of this study was to investigate how exhaustive exercise affects testosterone levels and plasma lactate in cyclists who were supplemented with oral zinc and selenium for 4 weeks. For this reason, 32 male road cyclists were selected equally to four groups: PL group, placebo; Zn group, zinc supplement (30 mg/day); Se group, selenium supplement (200 μg/day); and Zn-Se group, zinc-selenium supplement. After treatment, free, total testosterone, and lactate levels of subjects were determined before and after exhaustive exercise. Resting total, free testosterone, and lactate levels did not differ significantly between groups, and were increased by exercise (P > 0.05). Serum total testosterone levels in Zn group were higher than in Se group after exercise (P < 0.05). Serum-free testosterone levels in the Zn group were higher than the other groups (P < 0.05).There was an insignificant difference between levels of lactate in the four groups after exercise (P > 0.05). The results showed that 4-week simultaneous and separately zinc and selenium supplementation had no significant effect on resting testosterone and lactate levels of subjects who consume a zinc and selenium sufficient diet. It might be possible that the effect of zinc supplementation on free testosterone depends on exercise.

Aspectos sobre a relação entre exercício físico, estresse oxidativo e zinco

Este trabalho visa a contribuir com informações sobre a relação entre exercício físico, estresse oxidativo e zinco. A formação de espécies reativas de oxigênio durante o exercício pode contribuir para danos tissulares e celulares, prejudicando o desempenho do atleta. Podem amenizar esses efeitos alguns minerais, como o zinco, que atuam como cofator da enzima superóxido dismutase e na regulação da síntese da metalotioneína, proteínas importantes no sistema de defesa antioxidante. No exercício físico, ocorrem distúrbios na compartimentalização do zinco, com alterações da concentração desse mineral em compartimentos celulares. No entanto, os mecanismos envolvidos no comportamento metabólico do zinco bem como a participação do mineral na melhora do desempenho físico ainda não estão totalmente esclarecidos. Dessa forma, conclui-se que a distribuição do zinco em organismos submetidos ao estresse oxidativo e os efeitos da deficiência desse mineral na capacidade antioxidante durante o exercício ainda devem ser pesquisados mais profundamente.

The time of day and the interval since previous meal are associated with plasma zinc concentrations and affect estimated risk of zinc deficiency in young children in Peru and Ecuador

BACKGROUND/OBJECTIVES

Plasma zinc concentration is the preferred biomarker of zinc status, but the time of day and time since previous meals can modify the results. Measuring fasting plasma zinc concentration is not feasible among young children, so adjustments need to be developed for interpreting results. Our objective is to develop correction factors to adjust for the effects of time of day and interval since the previous meal when measuring plasma zinc concentrations of young children.

SUBJECTS/METHODS

We measured plasma zinc concentrations among young Peruvian (n =297) and Ecuadorian (n=466) children, and constructed regression models adjusting for time of day, interval since previous meal and infections.

RESULTS

Plasma zinc concentrations were positively related to the number of hours since the previous meal in the Peru trial (r =0.22, P<0.0001) and negatively related to the time of day of blood sampling in both Peru (r = -0.24, P<0.0001) and Ecuador (r = -0.18, P<0.001). In multivariate models, plasma zinc concentrations were ~2 μg per 100 ml less for each hour later in the morning when blood samples were collected, in both populations, and concentrations were ~1.0 μg per 100 ml greater for every hour since previous meal consumption in Peru. The percentage of children with low plasma zinc concentrations varied according to both these factors.

CONCLUSIONS

The time of day and the interval since the preceding meal should be recorded when measuring plasma zinc concentration and incorporated into the statistical analysis and interpretation when assessing population zinc status.

Knockdown of metallothionein 1 and 2 does not affect atrophy or oxidant activity in a novel in vitro model

Skeletal muscle atrophy is a significant health problem that results in decreased muscle size and function and has been associated with increases in oxidative stress. The molecular mechanisms that regulate muscle atrophy, however, are largely unknown. The metallothioneins (MT), a family of genes with antioxidant properties, have been found to be consistently upregulated during muscle atrophy, although their function during muscle atrophy is unknown. Therefore, we hypothesized that MT knockdown would result in greater oxidative stress and an enhanced atrophy response in C(2)C(12) myotubes subjected to serum reduction (SR), a novel atrophy-inducing stimulus. Forty-eight hours before SR, myotubes were transfected with small interfering RNA (siRNA) sequences designed to decrease MT expression. Muscle atrophy and oxidative stress were then measured at baseline and for 72 h following SR. Muscle atrophy was quantified by immunocytochemistry and myotube diameter measurements. Oxidative stress was measured using the fluorescent probe 5-(and-6)-carboxy-2',7'-dichlorodihydrofluorescein. SR resulted in a significant increase in oxidative stress and a decrease in myotube size and protein content. However, there were no differences observed in the extent of muscle atrophy or oxidant activity following MT knockdown. We therefore conclude that the novel SR model results in a strong atrophy response and an increase in oxidant activity in cultured myotubes and that knockdown of MT does not affect that response.

Consumption of a moderately Zn-deficient and Zn-supplemented diet affects soluble protein expression in rat soleus muscle

Zinc deficiency negatively affects muscle function, but there are limited biochemical data identifying the cause of this reduction in function. The objective of the present study was to identify soluble proteins in rat soleus muscle that were responsive to different levels of dietary zinc. Rats (n=21) were fed diets containing three concentrations of zinc: 5, 30 and 200 ppm for 42 days. There was no difference in body weights of the rats consuming the 5-ppm zinc diet compared to the rats consuming the 30- or 200-ppm zinc diets; however, bone zinc levels were significantly decreased in the 5-ppm dietary zinc group. Individual soluble protein fractions were isolated from these muscles and the samples were prepared for two-dimensional polyacrylamide gel electrophoresis. The expression levels of four proteins were significantly depressed by dietary Zn depletion and supplementation, S-glutathiolated carbonic anhydrase, myosin light polypeptide 3, heat shock protein 20 and heart fatty acid binding protein. This is the first report that indicates that both Zn depletion and supplementation result in protein expression profiles that may negatively affect skeletal muscle function. These results indicate that there are specific signaling pathways that require proper Zn nutriture for maintaining optimal muscle function and suggest that the consumption of pharmacologic doses of Zn may be detrimental to muscle function.

Effect of zinc supplementation on thyroid hormone function. A case study of two college females

BACKGROUND/AIMS

Zinc is crucial for proper thyroid hormone metabolism; zinc deficiency may result in decreased thyroid hormone levels and resting metabolic rate (RMR). The purpose of this investigation was to assess the effects of zinc supplementation on plasma zinc, serum ferritin, plasma total triiodothyronine (T(3)) and thyroxine (T(4)), serum free T(3) and T(4), and thyroid-stimulating hormone concentrations, and RMR in zinc-deficient, physically active women.

METHODS

Two zinc-deficient female college students (ZD1 and ZD2) were supplemented with 26.4 mg/day of zinc (as zinc gluconate), and the above parameters were analyzed at 0, 2 and 4 months.

RESULTS

Zinc deficiency was clinically corrected in both subjects, while serum ferritin concentration declined to classify both subjects as borderline iron deficient (ZD1 = 15.3 and ZD2 = 15.3 ng/ml at 4 months). At 4 months, total T(3) concentrations increased in ZD1, while all thyroid hormone concentrations increased in ZD2. RMR increased in both subjects by 4 months.

CONCLUSION

Zinc supplementation appeared to be directly responsible for the increase in plasma zinc and decline in serum ferritin concentrations in both subjects. Zinc supplementation appeared to have a favorable effect on thyroid hormone levels, particularly total T(3), and RMR.

Effect of maximal exercise on the short-term kinetics of zinc metabolism in sedentary men

OBJECTIVE

To examine the effect of acute exhaustive exercise versus rest on short-term zinc kinetics in men.

DESIGN

Crossover design, wherein all subjects were their own control.

SETTING

University setting, where subjects were free living.

PARTICIPANTS

12 healthy, sedentary men, 25-35 years of age.

INTERVENTIONS

(70)Zn was infused 10 min after exercise or at rest. Plasma zinc concentrations were measured at baseline and 2, 5, 10, 15, 30, 45, 60, 75, 90 and 120 min after exercise or rest. Haematocrit was measured before and after exercise to assess changes in plasma volume.

MAIN OUTCOME MEASUREMENTS

Plasma zinc (primary), serum creatine kinase and serum cortisol concentrations (secondary).

RESULTS

Plasma zinc concentrations decreased (p<0.05) after exercise, with a mean (SD) nadir of 13.9% (4.1%) observed at 70 min after exercise. There were increases in the size of the rapidly exchangeable plasma zinc pool (Qa; from 3.1 (0.2) to 3.6 (0.2) mg; p<0.05) and the liver zinc pool (Qb; from 10.2 (0.6) to 11.4 (0.8) mg; p = 0.12).

CONCLUSION

Exercise seems to cause a shift of plasma zinc into the interstitial fluid and liver after exercise, which may reflect the acute stress response of strenuous exercise.