View all posts

Zinc Supplementation on Trial: What does the Research Say?

By Neel Duggal, April 2, 2015

Manufacturers of zinc supplements such as ZMA claim that consuming their products will boost your testosterone, strengthen your immunity, and improve your athletic performance. But are these lofty claims backed up by credible research? And is there really a need for athletes and the general population to consume these supplements? Read below to find out why you need to regularly monitor your zinc status and if regularly taking zinc supplements can enhance your health and athletic performance.

Zinc_Bottle

Why Do You Need Zinc?

Zinc is required for many biological processes such as cellular growth, maintenance of the nervous system, and immunity [1]. At a molecular level, zinc is involved in processes supporting life such as cellular respiration, DNA reproduction, preservation of cell membranes, and elimination of substances called radicals which contribute to aging [1]. Because of its incredible variety of functions in your body, zinc is required for the activity of over 300 enzymes [2]. Zinc is found in all tissues and fluids and the total zinc content in the human body is estimated to be 2 g [3]. Zinc is also an essential micronutrient.  This means that it cannot be produced by the body itself and can only be acquired through foods or dietary supplements [4]. It is naturally found in protein-rich foods such as meat, shellfish, wholegrains, and legumes (Fun Fact: Oysters are known to have the highest zinc content!).

Un-optimized levels of zinc can wreak havoc in your body. Zinc deficiency can lead to conditions associated with fatigue such as lethargy and anorexia [5]. It can also impair immune function and increase susceptibility to infection, harm kidney function, and hamper tissue growth [6]. Similarly, excess levels of zinc resulting from consuming high dose supplements and too many zinc-heavy foods can result in kidney problems, impair cardiac function, and inhibit digestive enzymes such as lipase (fat-digesting) and amylase (starch-digesting) [5]. Overall, zinc-deficiency is much more common than zinc excess [6].

Getting your zinc levels tested using services such as InsideTracker can determine if your levels of zinc are optimized based on your internal biochemistry and lifestyle factors. But are you at risk for zinc deficiency?

Key Takeaways: Regularly monitoring for adequate levels of zinc is crucial for maintaining proper bodily function

Zinc Deficiency: How Common is it and who is at Risk?

Some researchers claim that 2 billion people- or about 30% of the world’s population- is zinc-deficient [1]. In the US, approximately 12 percent of people do not consume enough zinc in their diets [1]. This isn’t as common compared to other nutrient deficiencies we see at InsideTracker, such as vitamin D, that we observe in over 70% of our clinical population. That being said, certain populations are more likely to suffer than others from zinc deficiency. Older adults tend to eat fewer zinc-rich foods and their bodies no longer use or absorb zinc optimally, making them highly susceptible to zinc deficiency. In fact, of those 65 and older, the literature states that approximately 40 percent consume insufficient zinc [1].

We most commonly observe zinc deficiencies in two other populations: athletes and vegetarians. The nutritional habits of elite athletes, which comprise a little over 10% of our clinical population, are quite different from the recommended diet for the average American. Endurance athletes in particular, such as swimmers and runners, often increase carbohydrates and lower intake of proteins and fat. According to literature, this change may lead to suboptimal zinc intake in up to 90% of athletes [7]. Mild zinc deficiency using your standard physician’s blood test is difficult to detect because of the lack of personalization in these assessments. However, in athletes, zinc deficiency can lead to significant loss of bodyweight, fatigue with decreased endurance, and an increased risk of osteoporosis [7]. All of this, of course, leads to deterioration of athletic performance and general health.

Because many zinc-rich foods are animal-based, zinc deficiency is more commonly observed in vegetarians and vegans. A recent meta-analysis of 26 studies comparing males and females consuming vegetarian diets with non-vegetarian groups revealed that vegetarian populations, on average, have 8-12% lower serum zinc concentrations [8]. This deficiency is even more pronounced in female vegetarians, vegetarians from developing countries, and vegans [8].

As one would expect, vegetarian athletes (especially those over the age of 65!) are most at risk for zinc deficiency. However, can zinc supplementation actually improve quality of health and boost athletic performance?

Key Takeaways: Zinc deficiency is a common problem among Americans. Vegetarians, elderly, and athletes are more likely than average to suffer from zinc deficiency due to specialized diets. 

Zinc Supplementation to Treat Deficiency: Does it make a Difference?

Oysters

 

Provided the issues vegetarians encounter with zinc, the researchers of the meta-analysis study concluded that:

“Dietary practices that increase zinc bioavailability, the consumption of foods fortified with zinc or low-dose supplementation are strategies that should be considered for improving the zinc status of vegetarians with low zinc intakes or serum zinc concentrations at the lower end of the reference range” [8].

For vegans specifically, another group of researchers stated that “unless vegans regularly consume foods that are fortified with these nutrients, appropriate supplements should be consumed” [9]. It is important to note that there have been no intervention studies assessing the impact of supplementation on zinc-deficient vegetarians. Additionally, not all vegetarians are zinc-deficient; you can only prove that by getting a proper blood test.

Zinc supplements may be particularly helpful in counteracting aging for elderly individuals who are already deficient in zinc. In 2014, researchers recruited 84 elderly volunteers for a 12 week placebo-controlled intervention trial with 42 subjects in the placebo group and 42 subjects in the zinc-supplement intervention group. At the study’s conclusion, plasma Zn was increased by 5.69% in the Zn supplemented group [10]. Researchers also observed significant improvements in key aging indicators in this group including a decrease in micronucleus frequency and reduced telomere damage. Because of these findings, the authors concluded that “Zn supplementation may have a beneficial effect in an elderly population with low Zn levels by improving Zn status, antioxidant profile and lowering DNA damage” [10].

Because zinc is involved in cellular processes related to diabetes- a condition which commonly affects older adults - researchers have recently begun to assess if zinc supplements can help treat symptoms of diabetes. In one study, providing type 2 diabetics with a low dose supplement of 30 mg/day of zinc for six months reduced a common measure of aging without affecting blood glucose [11]. In contrast, a placebo-controlled study in 40 men with type 2 diabetes and normal levels of zinc found that high-dose zinc supplementation (240 mg/day) for three months did not improve measures of aging or vascular function [12]. Given these findings, a low dose supplementation of zinc might be useful in reducing aging-related effects of diseases such as diabetes in zinc-deficient populations. However, more research needs to be done to confirm this. 

Key Takeaways: Low dose zinc supplements are useful for populations that suffer from zinc deficiency such as vegetarians and the elderly. However, the benefits of supplementation are not fully understood in treating symptoms of aging-related diseases such as Type II diabetes.

The Other Side of the Zinc Coin: Zinc Excess 

Zinc_Normal

The last time I got my InsideTracker test, I was surprised to see that my zinc levels were no longer in the optimal zone. Instead, they had elevated to the middle of the clinically acceptable range- putting me well above my optimal zone. While clinical zinc deficiency is more common than clinical zinc excess, we observe zinc levels at the high end of the clinically accepted zone in almost 50 % of our clinical population. So, what does the research say about zinc excess?

Research supports the notion that excessive zinc supplementation is known to have adverse effects on the digestive and urinary systems. In a long-term, randomized trial of 3,640 patients over 6 years, researchers experimented with four different treatments: two that included 80 mg zinc supplements and two that didn’t. After analyzing the data, researchers found a significant increase in hospital admissions due to genitourinary causes in the patients who consumed the zinc supplement vs. the ones who did not (11.1% vs 7.6%) [13]. This was even more pronounced in males. When comparing the subjects who took zinc compared to the ones who didn’t, researchers noticed significant increases in urinary tract infections especially in females (2.3% vs 0.4%) [13]. Thus, researchers concluded “these data support the hypothesis that high dose zinc supplementation has a negative effect on select aspects of urinary physiology” [13]. 

An older but credible study from the Journal of American Medical Association showed that excess zinc supplementation resulted in lower levels of HDL cholesterol- the form of cholesterol that lowers arterial clogging. In their study, twelve healthy adult men ingested an equivalent of 160 mg of zinc per day for five weeks. At the end of the intervention, high-density lipoprotein-cholesterol concentration decreased 25% below baseline values (40.5 to 30.1 mg/dL) [14]. The authors concluded that “zinc [supplementation] may be atherogenic in men”, meaning that it increases your chance of developing cardiovascular disease [14]. This study was supported by a similar but more precise study in women. In it, researchers provided 32 women for 8 weeks with either a placebo, 15 mg supplement of zinc, 50 mg supplement of zinc, or 100 mg supplement each day. At the end of the study, researchers observed no significant differences in HDL cholesterol levels except in the 100 mg supplement group which experienced an 8.7% decrease in HDL levels [15]. 

Key Takeaways: Because many people commonly fall under the clinically acceptable range of zinc levels, regularly taking high dose zinc supplements (>50 mg) can harm the health of your urinary, digestive, and cardiovascular systems.

ZMA Supplementation for Athletes: Does it Work?

Pumpkins

 

Of all zinc-related supplements, manufacturers of ZMA have made the boldest claims about its product enhancing your health and athletic performance. ZMA is a natural mineral supplement that contains zinc along with magnesium aspartate (which increases your body’s magnesium) and vitamin B6. According to the company which produces ZMA, daily consumption of ZMA can increase your immunity and metabolism (because of Zinc), optimize your testosterone (because of magnesium), and boost energy for athletic performance (because of B6). Its manufacturers even claim that ZMA can benefit health and fitness even in people who already have adequate levels of zinc- meaning that one need not have zinc deficiency to obtain its proclaimed benefits. 

But are these bold claims supported by research? In a 2000 sport science study, researchers provided ZMA supplements to a group of 12 NCAA football players practicing twice a day for 7 weeks and compared them to a placebo group of 15 NCAA football players. At the conclusion of the intervention, they found a significant increase in the players’ levels of testosterone and growth hormone compared to the placebo group [16]. Despite these promising findings, the study was funded by the company that creates ZMA and one of the researchers who conducted the study helped patent the supplement’s formula. This means that its results, while promising, aren’t credible due to financial interest and personal bias. Another studies often cited by ZMA supporters were also funded by private interest groups and used poor methodologies [17].

The only third-party research study assessing ZMA does not support the notion that it benefits athletic performance or weight loss in populations that already have optimized levels of zinc. In 2006, scientists recruited fourteen healthy, regularly exercising men aged 22–33 years with clinically healthy levels of zinc. According to their group assignment, all subjects ingested either three capsules per day of ZMA or placebo for 56 days. At the conclusion of the study’s period, researchers only observed increased levels of zinc in the urine of the population that consumed ZMA- indicating that it may have induced toxicity in the body. As a result, they concluded that “the present data suggest that the use of ZMA has no significant effects regarding serum testosterone levels and the metabolism of testosterone in subjects who consume a zinc-sufficient diet” [18].

Key Takeaways: There are no proven benefits of ZMA on athletes with adequate zinc and magnesium. In fact, consuming it might be harmful. 

The Verdict on ZMA

Because of the inconclusive research on ZMA, InsideTracker does not recommend consuming ZMA if you already have optimized levels of zinc or magnesium or if you are unaware of your levels of these minerals. That being said, if your InsideTracker results show deficiencies in both zinc and magnesium, we recommend that you consume ZMA. Magnesium deficiency is even more common than zinc deficiency and affects an estimated 50% of Americans [19]. Additionally, there is compelling research to suggest that correcting deficiencies in both of these nutrients can help optimize other biomarkers including testosterone, c-Reactive Protein, and white blood cell count. Again, it is important to regularly monitor your zinc (and magnesium) levels in order to make sure that you avoid the negative effects of zinc toxicity we mentioned above and look at your other health and biomarker data.

Key Takeaways: ZMA may be beneficial to athletes and non-athletes alike who are proven through blood testing to be deficient in zinc and magnesium.

Metallic Connection: Zinc Supplementation and Your Body

The research shows that you need to know your zinc levels and make the appropriate changes to avoid health concerns associated with both deficiency and excess. InsideTracker provides personalized lifestyle and dietary recommendations on how you can modify your zinc status based on YOUR individual data and habits. If you would like to know if zinc supplementation is for you, click below to learn your zinc levels along with 29 other key biomarkers.

 

Check Your Deficiencies

 

List of References

[1] Prasad, Ananda S. "Discovery of human zinc deficiency: 50 years later." Journal of Trace Elements in Medicine and Biology 26.2 (2012): 66-69.

[2] McCall, Keith A., Chih-chin Huang, and Carol A. Fierke. "Function and mechanism of zinc metalloenzymes." The Journal of nutrition 130.5 (2000): 1437S-1446S.

[3] Human Vitamin and Mineral requirements, Chapter 16. Zinc; Agriculture and Consumer Protection Department, Food and Agriculture Organization of the United Nations, 2002

[4] Zinc - Fact Sheet for Health Professionals; Office of Dietary Supplements, National Institutes of Health, June 2013.

[5] Risk Assessment - Zinc; Expert Group on Vitamins and Minerals, 2003

[6] Plum, Laura M., Lothar Rink, and Hajo Haase. "The essential toxin: impact of zinc on human health." International journal of environmental research and public health 7.4 (2010): 1342-1365.

[7] Micheletti, Alessandra, Ruggero Rossi, and Stefano Rufini. "Zinc status in athletes." Sports medicine 31.8 (2001): 577-582.

[8] Foster, Meika, et al. "Effect of vegetarian diets on zinc status: a systematic review and meta‐analysis of studies in humans." Journal of the Science of Food and Agriculture 93.10 (2013): 2362-2371.

[9] Craig, Winston J. "Health effects of vegan diets." The American journal of clinical nutrition 89.5 (2009): 1627S-1633S.

[10] Sharif, Razinah, et al. "Zinc supplementation influences genomic stability biomarkers, antioxidant activity and zinc transporter genes in an elderly Australian population with low zinc status." Molecular nutrition & food research (2015).

[11] Anderson, Richard A., et al. "Potential antioxidant effects of zinc and chromium supplementation in people with type 2 diabetes mellitus." Journal of the American College of Nutrition 20.3 (2001): 212-218.

[12]  Seet RC, Lee CY, Lim EC, et al. Oral zinc supplementation does not improve oxidative stress or vascular function in patients with type 2 diabetes with normal zinc levels. Atherosclerosis. 2011;219(1):231-239. 

[13] Johnson, Aaron R., et al. "High dose zinc increases hospital admissions due to genitourinary complications." The Journal of urology 177.2 (2007): 639-643.

[14] Hooper, Philip L., et al. "Zinc lowers high-density lipoprotein-cholesterol levels."Jama 244.17 (1980): 1960-1961.

[15] Freeland-Graves JH, Friedman BJ, Han WH, Shorey RL, Young R. Effect of zinc supplementation on plasma high-density lipoprotein cholesterol and zinc. Am. J. Clin. Nutr. 1982;35:988–992.

[16] Brilla, L. R., and Victor Conte. "Effects of a novel zinc-magnesium formulation on hormones and strength." J Exerc Physiol Online 3.4 (2000): 26-36.

[17] Wilborn, Colin D., et al. "Effects of zinc magnesium aspartate (ZMA) supplementation on training adaptations and markers of anabolism and catabolism." J Int Soc Sports Nutr 1.2 (2004): 12-20.

[18] Koehler, K., et al. "Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement." European journal of clinical nutrition 63.1 (2009): 65-70.

[19] Community Nutrition Mapping Project. "Nutrient Intakes Percent of population 2 years old and over with adequate intakes based on average requiremens". 2009-07-29.