Zinc supplements may or may not be needed depending on several factors which will be covered shortly but first a bit about zinc, chemical symbol Zn, is in order.
It is an essential trace mineral with a Recommended Dietary Allowance (RDA) of 11 mg/day for adult males and 8 mg/day for adult females.
Being a trace mineral the amount needed is very small. Most people have a pretty good feel for the quantity represented by an ounce. In ounces, the RDA for men is .000388 oz and women is .000282 oz.
Zinc only makes up around .0075% of the earth's crust making it the 24th most abundant element. The zinc content of soil and seawater is measured in parts per million and parts per billion where soil contains an average 64 ppm and seawater has about 30 ppb. That's pretty small potatoes as earth's elements go.
It is very well known as an industrial metal but not so well known for its health properties. Industrially we know zinc as being used to galvanize metals to prevent corrosion.
Look at all those highway guardrails and chain link fences and what you see is zinc. It is also well known to be an important component in alloyed metals such as brass, bronze, nickel silver and aluminum solder.
Remember the copper penny? There's not much copper in the U.S. penny anymore; it is mostly a zinc core with a thin copper coating.
Our interest here is in the health benefits and whether or not zinc supplements are needed. Most people know about zinc supplements and the zinc throat lozenges that are believed to lessen cold symptoms and shorten its duration.
Beyond that the real role of zinc is somewhat of a mystery. What do those 11mg/day and 8mg/day of zinc do for us? Here's a hint; it's a lot more than just mitigating a cold.
There is about 2 to 4 grams of zinc throughout the human body with most of it concentrated in the brain, muscle, bones, kidney and liver but the highest concentrations are in the eyes and prostate.
Not so coincidentally, semen is very rich in zinc which indicates a strong role in prostate function as well as growth of the male reproductive organs. No kidding! Without a doubt, this is why zinc supplements are thought to help prevent or mitigate prostate cancer but more on that shortly.
First off, zinc has a very active role in enzyme activity. It is found in between 100 and 300 specific enzymes and acts as structural ions in controlling the flow of genetic information from DNA to messenger RNA (mRNA).
It is also stored and transferred in a family of proteins found in the Golgi apparatus of cells where they have the ability to bind to both toxic heavy metals like cadmium, arsenic and mercury.
In this role it is thought that zinc contributes to detoxifying the body of dangerous heavy metals through these proteins known as metallothioneins.
This family of proteins can also bind to lighter physiological metals like zinc, selenium and copper where it appears that they have a role in regulating these metals and reducing oxidatative stress. Without zinc, it is likely that these processes could not proceed.
It appears to have a role in regulating apoptosis, the pre-programmed cell death.
In the brain zinc is stored in synaptic vesicles, the tiny reservoirs that also store neurotransmitters, where the contents are released into the neuron synapse as needed.
The indication is that zinc plays a role in controlling brain excitability, synapse plasticity (the ability of a synapse to change in strength in response to the degree of usage) and thus learning.
There is a cell signaling function as well. Cells in the salivary glands, prostate, immune system and GI tract use zinc signaling to communicate with other cells.
Zinc enables or contributes to a huge number of biological processes of which only a few have been touched on here. This is a very, very important element to the proper functioning and homeostasis of our body.
Zinc is relatively plentiful in many foods including meats, beans, nuts, whole grains, edible seeds (sunflower, pumpkin, sesame etc.) and produce raised in zinc rich soil.
On top of the natural food sources, there are a number of common zinc fortified foods such as breakfast cereals.
Add to that zinc has many different forms including zinc oxide, zinc carbonate, zinc sulfate, zinc acetate, zinc picolinate, zinc gluconate and zinc glycinate.
When it comes to zinc supplements however, there are only four
available for dietary consumption: oxide, carbonate, sulfate and glycinate.
As we saw with the various magnesium supplements, absorption and bioavailability mattered. The same is true of zinc supplements.
An older study in 1998 showed that two very common zinc supplements, the oxide and carbonate, are nearly insoluble and very poorly absorbed in the body.
A later study in 2003 showed that zinc oxide in fortified foods, such as cereals, were as easily absorbed as the more expensive zinc supplements.
A 2005 study looking at fortification in foods of countries exhibiting high rates of zinc deficiency, specifically Mexico, showed that when corn tortillas were fortified with zinc oxide or zinc sulfate, there was no statistical difference in absorption.
A very recent study in 2008 concluded that zinc glycinate was the best absorbed of the four zinc supplements on the market.
While zinc deficiencies in the U.S. are not particularly common, there are many special conditions that could lead to low blood levels of zinc.
Worldwide, the most common cause of zinc deficiency is inadequate dietary consumption where it is estimated that over two billion people suffer from a zinc deficiency and contributes to the deaths of around 800,000 children per year.
In the U.S., deficiencies are more likely to be caused by malabsorption from disease conditions such as chronic liver and kidney disease, sickle cell, diabetes, various malignancies and a genetic metabolic disorder called acrodermatitis enteropathica that retards the uptake of zinc.
Symptoms of zinc deficiency are quite diverse and range from mild to severe and include retarded growth, diarrhea, impotence, delayed sexual maturity, hair loss (alopecia), eye and skin lesions, impaired cognition, impaired immune response and inadequate carbohydrate usage.
Suspected zinc deficiencies are very hard to diagnose and many of the symptoms can be caused by several health impairments. Nevertheless, there are several conditions where zinc supplements have proven effective.
Age related macular degeneration, the genetic acrodermatitis enteropathica, gastroenteritis, wound healing and reduction of
oxidative stress are among the positive outcomes of zinc supplementation.
Over indulgence in zinc supplements along with high zinc content foods can be toxic and dangerous to our health. For example copper and iron are essential minerals that we need to sustain life but an excess of zinc inhibits the absorption of both.
Zinc toxicity is sometimes a problem among the affluent that take a lot of dietary supplements as well as eat a diet of fortified foods.
The U.S. National Research Council has set a Tolerable Upper Intake of 40 mg/day but many healthcare providers hold that healthy people should not exceed 20 mg/day.
It would be inadvisable to exceed 20 mg/day and extremely foolhardy to go over the tolerable limit of 40 mg. Take a lesson from the plants; with too little zinc they are susceptible to disease and growth retardation.
With too much zinc, they have trouble absorbing iron and manganese and other trace minerals. In the plant world, "just right" is the goal.
With humans problems start appearing around 80 mg/day and really get serious above 100 mg/day. For starters iron and copper absorption goes down the tubes and hospitalizations for urinary complications resulted from elderly men consuming 80 mg/day.
At levels between 100-300 mg/day immune function can be impaired and disruptions in the LDL:HDL ratio is seen.
At levels just slightly above the RDA, say in the 15-20 mg/day range, some utilization of copper and iron has been noted as well as adversely affecting HDL concentrations.
Zinc poisoning, zinc toxicosis, is generally the result of accidental ingestion of free zinc ions. For example, since 1982 the U.S. penny is constructed by coating a zinc core with a thin copper coating.
If one or more of these pennies is swallowed, for example by a child, hydrochloric acid in the stomach will quickly erode the copper coating and easily dissolve the metallic zinc.
Zinc being acted on by hydrochloric acid produces highly corrosive zinc chloride which can damage the lining of the stomach. Just such occurrences have caused fatalities in both children and adults.
Ingestion of free zinc ions, from whatever source, by dogs and other animals and especially birds such as parrots if fatal.
In dogs death is from kidney or liver failure. Parrots have experienced mass poisonings from being given fruit juice that had been stored in galvanized cans.
Anyone taking zinc supplements must be aware of potential toxicity and carefully monitor their total zinc intake.
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