Zinc and ZMA Technical Document Developed by INDI/SNIG for the Irish Sports Council 2009
Table of Contents Introduction 3 The health benefit claims for consuming zinc supplements 3 The athletic benefits of consuming zinc supplements 3 Recommended zinc dosage 3 Concerns with zinc supplementation 4 Zinc monomethionine aspartate and Magnesium aspartate (ZMA) 4 The claimed benefits for consuming ZMA 4 The athletic benefits of consuming ZMA 5 ZMA dosage 5 Concerns with ZMA supplementation 5 Summary of ZMA Literature 5 Notes 6 References 7 2
Introduction Zinc is an essential trace element which plays an important role in all living human cells. Zinc can be found in all tissues and fluids within our bodies, with the majority found in skeletal muscle and bones (de Oliveira et al. 2009, Arikan et al. 2008, Volpe, 2008). Zinc plays an important role in exercise metabolism, with studies demonstrating that athletes or individuals who recreationally train are at a higher risk of zinc deficiency (Arikan et al. 2008, Nieman and Pedersen 1999, Nieman 1999). Arikan (2008) showed serum zinc levels were less in national team weightlifters than in a sedentary group, but all appeared to be within the normal range, so it is questionable as to whether this has any real significance. Although studies have shown that athletes may have lower plasma zinc levels during heavy training periods, those lower plasma zinc levels reported for the majority of athletes usually remain within normal clinical ranges (Volpe 2008, Volpe 2007, Kilic et al. 2006, Peake et al. 2003). Zinc can be found in many foods such as meat, liver, eggs, seafood (especially shellfish and oysters), and in smaller amounts in nuts, legumes, wholegrains, miso, tofu, brewers yeast, mushrooms, green beans and pumpkin seeds. Zinc can also be purchased as a nutritional supplement in isolation as a tablet, as part of multivitamins and in conjunction with other minerals such as magnesium in supplements such as ZMA (see below). Zinc is an essential mineral that is present in some foods and imperative to the normal physiological functioning of the human body. It plays a role in maintaining normal growth and development, immune function, wound healing, taste and smell to name a few. This technical document and factsheet will only focus on zinc supplementation in athletes and exercise. The health benefit claims for consuming zinc supplements The main purported benefit of zinc supplementation revolves around enhancing immune function. Reported benefits include reducing the risk of the common cold and other infectious diseases (Maughan et al 2004, Gleeson et al. 2004). A review by Maughan et al (2004) reported that the findings of studies assessing supplementation with zinc to combat the symptoms of the common cold were inconclusive and unclear. Whilst some studies suggested favourable outcomes for decreasing the symptoms of common colds when supplementation was commenced within 24 hours from the onset of symptoms (Mossad et al. 1996), others did not (Mackinnon et al. 1998). While zinc has been shown to be important for maintaining immune function, excessive consumption of certain micronutrients, including zinc, can also impair immune function and have other adverse effects on health such as an increased risk of infection (Gleeson et al. 2004). For more detailed reviews of zinc supplementation and immune function in athletes please refer to Maughan et al. (2004) and Gleeson (2004). The athletic benefits of consuming zinc supplements Low plasma zinc levels have been associated with reductions in RBC carbonic anhydrase activities, and impaired metabolic responses during exercise (Lukaski et al. 2005). Therefore if an athlete is zinc deficient, supplementation may prevent these outcomes that may impair exercise performance. However, analysis of the current body of literature, would suggest that there is no athletic benefit from consuming zinc supplements unless there is initially a clinical deficiency. Furthermore, there is no evidence to suggest that higher than normal levels of plasma zinc correlate to a performance benefit. Recommended zinc dosage Zinc requirements are higher in athletes than sedentary individuals because of increased losses in sweat and urine (Gleeson et al. 2004), but zinc lost through sweat has been shown to decrease after environmental acclimatisation (Chinevere et al. 2008, Montain et al. 2007). 3
The currently recommended dietary allowances for zinc from all sources (food and supplementation) are summarised in Table 1. Table 1: Recommended Dietary allowances for Ireland Age RDA (mg/day) Males 11-18 15 19-64 15 65+ 15 Females 11-14 15 15-18 15 19-64 15 65+ 15 Source: Food Safety Authority of Ireland, 1999 Concerns with zinc supplementation Studies have demonstrated that chronic zinc supplementation can reduce plasma copper and iron levels (de Oliveira 2009, Maxwell et al. 2007) which may have negative effects on athletic performance. Other reported adverse effects of zinc supplementation include nausea and bad taste reactions (Mossad et al. 1996, Maughan et al. 2004). Zinc monomethionine aspartate and Magnesium aspartate (ZMA) Zinc monomethionine aspartate and Magnesium aspartate, or ZMA as it is commercially known, is a combination of zinc, magnesium and vitamin B6. As zinc and magnesium individually are involved in many physiological processes that affect exercise, the combination of both known as ZMA has claimed to enhance athletic performance. Zinc has been purported to increase testosterone levels (Brilla et al. 2000) but this has predominantly been demonstrated in those with zinc deficiencies (Prasad et al. 1996, Favier 1992, Haboubi et al. 1988). The claimed benefits for consuming ZMA Nutritional supplement companies claim the consumption of ZMA will increase testosterone levels, thereby increasing muscular strength. An increase in testosterone levels in athletes has only been reported in one scientific study by Brilla et al. (2000) in which footballers were undertaking intense and exhaustive exercise. Other studies have only demonstrated increases in testosterone in those with zinc deficiencies (Favier 1992) and in elderly men (Haboubi et al. 1988). In healthy exercising populations, Koehler et al. (2009) demonstrated no increase in testosterone, and Wilborn et al. (2004) demonstrated that ZMA consumption did not enhance resistance training adaptations in well trained males. See Table 2 for a summary of the literature. 4
The athletic benefits of consuming ZMA Taking into account published literature to date, supplementation with ZMA does not appear to elevate testosterone levels or lead to additional strength adaptations from resistance training. ZMA dosage The current available scientific literature does not support the supplementation of ZMA therefore, it is inappropriate to provide dosage guidelines. Concerns with ZMA supplementation Due to the high levels of elemental zinc in ZMA, it is conceivable that athletes may consume excessive amounts of zinc which may in turn impair iron and copper absorption (de Oliveira 2009, Maxwell et al. 2007). Iron deficiency may compromise physical performance, through increased heart rate response, increased lactic acid build up and prolonged recovery time. Iron absorption and metabolism is dependent on a copper carrying protein, therefore copper deficiency can also negatively impact on performance (www.sportsci.org/encyc/drafts/iron_status.doc). Summary of ZMA Literature Table 2 Summary of ZMA Literature Reference Subjects Dose Sport / Exercise Protocol Performance Summary Brilla et al. 2000 27 male varsity football players 3 capsules of ZMA (30mg zinc monomethionine aspartate, 450 mg magnesium aspartate, and 10.5 mg vitamin B-6) or placebo for 7 weeks. Quadriceps and hamstrings isokinetic torque and power were assessed pre and post supplementation. Yes The study concluded ZMA was efficacious for strength trained athletes by increasing free testosterone. There was no exercise intervention assessed, only nutrition. Koehler et al. 2009 14 healthy men who exercised regularly on a recreational or semicompetitive basis 3 capsules of ZMA (30mg zinc monomethionine aspartate, 450 mg magnesium aspartate, and 10.5 mg vitamin B-6) or placebo for 8 weeks. No exercise intervention. Only blood zinc and testosterone levels assessed before and after supplementation. No increase in testosterone levels. The study demonstrated an increase in blood zinc however no increase in testosterone. Wilborn et al. 2004 42 resistance trained males 4 capsules of ZMA (11 mg of B-6, 450 mg of magnesium, 30 mg of zinc, 10 mg of potassium, and 706 mg of mucuna pruriens for 8 weeks. Resistance-training 4-day per week: two upper and two lower extremity workouts per week for a total of 8- weeks. No ZMA supplementation during training does not appear to enhance training adaptations in resistance trained populations. 5
Notes Pubmed (Medline) and SPORTDiscus were searched for all human studies published in peer reviewed journals in the last 5 years. The terms searched for zinc were: zinc, zinc AND exercise, and the search terms for ZMA were Zinc monomethionine aspartate and Magnesium aspartate, ZMA and ZMA AND exercise were used as key terms in all databases. The reference list from the zinc and ZMA articles retrieved were then searched for any additional land mark papers. Inclusion criteria Human studies published in English Healthy subjects Original investigations assessing the use of zinc or ZMA and exercise Incorporated the use of an indistinguishable placebo Exclusion Criteria Studies assessing Zinc or ZMA in a combination with another supplement Qualitative studies assessing supplement use in both the general and athletic population After title and abstract review, three original articles that assessed the use of ZMA in exercise settings were retrieved for review. There were no specific articles assessing the possible ergogenic effects of zinc and exercise. 6
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