Zinc supplementation: Worth the money?
By Fleur van Griensven
According to a recent poll and survey, you guys wanted to know more about zinc supplementation, so here you go! It’s a mineral not spoken much of, but that doesn’t necessary mean we should forget about it. What does this mineral do in the body? Are there any consequences of a low intake? Is zinc supplementation useful? You can read it all in this article: Zinc supplementation: worth the money?
What is Zinc?
Zinc is a mineral which is part of the trace elements in nutrition. Trace elements are minerals that are present in very small quantities in our diet, but are nonetheless essential. Other examples of trace elements are iodine and selenium.
Zinc is an essential element for hundreds of proteins in the body, including numerous enzymes and DNA-binding proteins. A few examples of proteins that contain zinc are the receptors for vitamin A and vitamin D. It also plays a role in immune function, wound healing and cell division. On top of that it also supports normal growth and development during pregnancy, childhood and adolescence[1].
Zinc can be found naturally present in some foods, it can be added to food, and it can be available as a dietary supplement. A wide variety of foods contain zinc. See table 1 below for an overview of the foods naturally containing zinc. Besides red meat and poultry, oysters are a great zinc source. Other good sources include nuts, beans, seafood, whole grains and dairy products.
*DV=Daily Value. The Daily Value by the U.S. Food and Drug Administration is 15 mg for adults and children older than 4 year. Note: Food labels do not need to list zinc content unless it is a fortified product.
Phytates, which are compounds presents in whole-grain breads, cereals, legumes (for example spinach) and some other foods, inhibit zinc absorption. This leads to a difference in bioavailability of zinc from plant foods compared to animal foods. Bioavailability is the fraction of the dose which you take that reaches the systemic circulation (blood circulation). This might seem rather complicated but I’ll try to explain it more clearly. When some medication is administered intravenously (directly into a vein) its bioavailability is 100% because it directly reaches the blood circulation. However, when a medication is administered orally its bioavailability is lower, since not all of it is absorbed in the intestine. Take home point: the bioavailability of zinc from plants foods is lower due to the fact that they inhibit zinc absorption, although many plant based foods are still good sources of zinc.
Supplements contain several forms of zinc, for example zinc gluconate, zinc sulfate and zinc acetate. In each of these forms the percentage of elemental zinc varies, but the elemental zinc content always appears on the supplement container. Research has not yet shown and determined whether differences exist among these forms of zinc in absorption and bioavailability.
Recommended intake
Zinc intake recommendations are provided in Recommended Dietary Allowances (‘Aanbevolen Dagelijkse Hoeveelheid’ in Dutch) developed by the Food and Nutrition Board (FNB). This is an average daily level of intake sufficient to meet the requirements of nearly all healthy individuals (97%). To see what the current RDA for zinc is, check table 2 below.
* Adequate Intake (AI)
What are consequences of a low zinc intake?
A zinc deficiency is characterized by growth retardation, loss of appetite and immune impairment. Especially immune impairment can lead to increased risk of getting infectious diseases. This is the case in developing countries as there is a bigger chance of zinc deficiencies. The prevalence (occurrence) of an inadequate zinc intake is >25% in Sub-Saharan and South Asia[3]. Most people in Western Countries and also the Netherlands have a wide variety of foods in their diet, which under normal circumstances should be enough to meet their RDI of zinc.
One study in 1995 made use of three conventional tests (serum, urine, and hair samples) in groups of Dutch children with symptoms common in zinc deficiency (diarrhea, recurrent infection, or growth retardation). From this study can be concluded that +/- 1% of Dutch children with minor complaints suffer from either acute or subacute zinc deficiency[4]. Thus zinc deficiency is not common among Dutch children.
There are more non-specific symptoms (weight loss, taste abnormalities and mental lethargy) which can result from a severe zinc deficiency, but these are often associated with other health conditions and a medical examination is needed in those cases.
Laboratory diagnosis of a zinc deficiency is difficult because zinc is distributed throughout the body and bound to various proteins. People can have symptoms of a zinc deficiency, but the laboratory tests might not confirm this.
However, there are some groups which may be at risk of zinc deficiency:
People with gastrointestinal diseases
Vegetarians
Pregnant women
Alcoholics
How about ZMA?
ZMA is a supplement widely used by bodybuilders these days. The supplement contains 2 minerals (zinc monomethionine aspartate and magnesium aspartate) and vitamin B6. It’s a supplement which claims to promote recovery and additionally raises strength levels and enhance hormonal profiles. Most labels indicate that it should be taken in 60-90 minutes prior to bedtime on an empty stomach.
Several scientific studies have been done on the effects of ZMA. One study in 2009 gave athletes the daily recommended dose of ZMA and measured androgen levels during the next 56 days. ZMA supplementation showed no effect on androgen levels between the placebo and ZMA group, so ZMA doesn’t elevate androgen levels[5]. In addition, most people don’t benefit from zinc and vitamin B6 supplementation, because they already meet the Recommended Dietary Allowances. Magnesium deficiencies are more common however.
This is just my own experience: I’ve used ZMA for a month or so, when I was cutting back in the days. I always have some problems falling asleep when I go deeper into a cut (because of the hunger, which keeps me awake during the night) and wanted to try out if it was any good. It sure made my muscles relax a bit more, but later I realized that I was better and cheaper off by just buying magnesium Citrate. Magnesium supplementation will be discussed in another article soon.
There are some claimed benefits from taking a zinc supplement. First, it states to accelerate wound healing and therefore zinc is being used to treat skin conditions such as ulcers. Relatively few studies support this. A meta-analysis of 181 participants from six randomized controlled trials of oral zinc sulfate versus placebo for venous or arterial leg ulcers found no significant difference in time between intervention and placebo group[6].
Secondly there is the claimed benefit on growth. A meta-analysis of 33 randomized controlled trials enrolling prepubertal children from North and South America, Europe, Africa, and Asia who were at risk of zinc deficiency showed that zinc supplementation modestly enhanced linear growth and weight gain. Growth responses were greater in children with low initial weight-for-age and in those with low initial height-for-age[7]. This only means that zinc supplementation can prevent a growth retardation. If you aren’t zinc deficient, it won’t make you grow.
Conclusion, zinc supplementation: worth the money?
In the end we can conclude that zinc supplementation isn’t necessarily needed provided you consume a healthy diet with a variety of different food sources. Food sources like red meat, poultry, nuts, dairy and whole grains all contain small quantities of zinc. There are however some risk groups which can benefit from taking a zinc supplement.
If you yourself experience some of the symptoms described above which might indicate a zinc deficiency, go and get your blood levels checked to see if this really is the case. The claimed effects of zinc supplementation are mixed. Most studies did not found a significant effect on wound healing. However on growth we see a modest improvement in children who were at risk of zinc deficiency. Take into account that zinc deficiency is rare in our country. So there is no added benefit of supplementing without actually suffering a zinc deficiency.
It can’t do any harm to eat more of the just mentioned food sources or take a zinc supplement if a deficiency really is the case. If not, you’re better off spending your money on food or other supplements which are in line with your personal situation!
References:
[1] EDX Nutrition and Health part 2: Micronutrients and Malnutrition. Available online: https://courses.edx.org/courses/course-v1:WageningenX+NUTR102x+1T2016/courseware/53a25d2c2f7c415fb9a713f9f6bbbc78/7e0877c1be994d539f67816ca52df564/
[2] National Institute of Health: Office of Dietary supplements. Available online: https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/
[3] K. Ryan Wessells and Kenneth H. Brown (2012). Estimating the Global Prevalence of Zinc Deficiency: Results Based on Zinc Availability in National Food Supplies and the Prevalence of Stunting. PLoS One. 7(11)
[4] Van Wouwe JP (1995). Clinical and laboratory assessment of zinc deficiency in Dutch children. A review. Biol Trace Elem Res. 49(2-3): 211-25.
[5] Koehler K, Parr MK, Geyer H, Mester J, Schänzer W (2009). Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. European Journal of Clinical Nutrition. 63(1): 65-70
[6] Wilkinson EA1, Hawke CI (1998). Does oral zinc aid the healing of chronic leg ulcers? A systematic literature review. Arch Dermatol. 134(12): 1556-60
[7] Brown KH1, Peerson JM, Rivera J, Allen LH (2002). Effect of supplemental zinc on the growth and serum zinc concentrations of prepubertal children: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 75(6): 1062-71.