What is zinc?
Zinc is an essential micronutrient that plays a considerable role in keeping the human body functioning optimally. It is involved in numerous vital functions including processing macronutrients, creating new cells and enzymes and wound healing. It also plays a major role in maintaining reproductive health, hormone function, maintaining testosterone levels, cardiovascular health and the absorption of fat-soluble vitamins. Zinc is excreted through urine and perspiration, which means it is particularly important for athletes to maintain adequate levels of the mineral. Low zinc levels have been shown to exacerbate the impact of stress on the body and accelerate the aging process.
What does it do?
Enzyme Function
Zinc is required for the activity of over 300 enzymes. Enzymes are molecules (typically proteins) that significantly speed the rate of most chemical reactions within cells. In proteins, zinc functions either as a direct chemical catalyst or plays a role in maintaining protein structure and stability.
Wound Healing
Zinc plays a regulatory role in every phase of the wound healing process. This process includes membrane repair, oxidative stress, coagulation, inflammation and immune defence, re-epithelialization (the reconstruction of skin cells) and scar tissue formation.
Immune System Function
Multiple aspects of the immune system are affected by zinc. It plays a crucial role in the normal development and function of cells mediating innate immunity (the defensive mechanisms within the body), neutrophils (white blood cells that lead immune system responses) and NK cells (white blood cells that play a role in rejection of tumours and virally infected cells).
Zinc also functions as an anti-oxidant meaning it plays a role in the prevention of free radical-induced injury during inflammatory processes.
Sense Of Taste and Smell
The ability to taste and smell is dependent on an enzyme called carbonic anhydrase which requires zinc to function. If zinc levels are inadequate, this enzyme is able to function correctly or may not be created in adequate amounts leading to a loss of the ability to taste and smell. People with low zinc levels often don’t enjoy eating a variety of foods, with protein being particularly disagreeable. In contrast, starchy foods tend to be more palatable. This is due to low zinc impacting the body’s ability to burn fat, which means it requires a constant influx of carbs to raise blood sugar.
Testosterone and Reproductive Health
Zinc is vital in maintaining normal testosterone status. A 1996 study showed that young men with normal testosterone levels experienced a drop of over 50% after 5 months of a low zinc diet. In the same study, older men who had low testosterone doubled their levels after zinc supplementation.
Low zinc has been shown to increase estrogen receptors and decrease androgen receptors and may increase the aromatization (or conversion) of testosterone to estrogen.
The mineral also plays a role in the development of male sex organs, individuals who are deficient have been found to have low sperm counts and under-developed testes. Some studies have also suggested a correlation between zinc deficiency and erectile dysfunction. In women, zinc plays a role in the growth process of the oocyte (or egg). Deficiencies can impede ovulation.
Exercise Performance
Insufficient zinc may lead to extra soreness after workouts and delayed recovery. This is due to the fact that this condition can lead to higher elevations of blood lactate levels during exercise. This will lead to greater fatigue and decreased power output. An inability to produce key performance hormones (like testosterone) will delay recovery from exercise.
Cardiovascular Health
The maintenance of healthy cardiovascular cells requires adequate zinc. The endothelium is a thin layer of cells that lines the blood vessels, playing a key role in circulation. Low zinc can lead to a deficiency in the endothelial barrier, leading to high cholesterol build up and inflammation. This in turn increases the risk of heart disease.
Insulin Health
Zinc binds to insulin so that adequate pancreas stores can be maintained and released when glucose enters the bloodstream. It also improves the insulin sensitivity of cells, meaning that the cell in question is receptive to insulin. It also makes up a component of the enzymes necessary for insulin to bind to cells, which allows glucose to enter and be utilised as fuel. Finally, zinc works as an anti-inflammatory, it helps to remove substances that cause inflammation in cells, preserving cell health and insulin sensitivity.
Neurological Health
The metabolism of melatonin, a key hormone for sleep, is dependent on zinc. It also plays a vital role in neurotransmitter function and cognition. It works as part of an enzyme that is necessary for the anabolism of fatty acids in the brain, meaning the brain is able to get the nutrients it needs to function.
Absorption of Fat-Soluble Vitamins
The intestinal absorption of fat-soluble vitamins- A, D, E and K is dependent on adequate zinc levels.
Dietary sources
Ideally, maintaining an optimal level of zinc will result from a diet consisting of foods rich in the mineral, such as:
- Shellfish (oysters, crabs, lobster, shrimp)
- Beef
- Pork
- Chicken
- Dairy products
- Oatmeal
- Seeds (e.g particular pumpkin, squash, pine nuts, chia, flaxseeds)
Legumes and nuts are also high in zinc, however they are also high in phytates which reduce your body’s ability to absorb the mineral.
How can you tell if you’re deficient?
Chronic zinc deficiencies are uncommon, however zinc levels that would be deemed ‘inadequate’ are surprisingly common in the developed world. It is more widespread in areas where the population eats a large amount of cereal and grain proteins. Research suggests up to 25% of American adults over 60 may have inadequate zinc levels. The figure for the total population could be as high as 40%. Certain lifestyle factors can increase the likelihood of a zinc deficiency. The mineral leaves the body through sweat, therefore athletes (who have a greater requirement for zinc to start with) are more at risk. In particular athletes who follow a high carb, low fat diet may suffer from inadequate zinc stores. Restrictive diets, such as keto or paleo, may lead to a lack of dietary zinc. Vegetarians and vegans are also at risk for this reason.
Taking certain medication can produce a deficiency, women taking birth control pills or undergoing hormone replacement therapy are at a greater risk.
Common symptoms of zinc deficiency include:
- Diarrhea
- Hair loss
- Eye and skin conditions
- Impotence, low libido or infertility
- Poor memory
- Slow wound healing
- Chronic fatigue
- Altered sense of taste (leading to cravings for saltier or sweeter food)
- Loss of appetite
- Weight loss
- Frequent illness (due to immune system weakness)
- Delayed recovery from exercise
The most accurate means of checking for a zinc deficiency is to get a red blood cell zinc test.
Another option is a zinc taste test. This involves placing a zinc sulfate product on the tongue. If it tastes like water you are likely deficient, a metallic taste may indicate zinc inadequacy. However this method is less reliable (particularly for those with a moderate deficiency) due to other factors that can affect taste.
Should you supplement?
The daily amount of zinc required is roughly:
9.5-11mg for adult men
7-8mg a day for adult women
It is possible to maintain adequate zinc levels purely from dietary sources, however as mentioned above there are certain populations that are more susceptible to deficiency. Before supplementing it’s important to assess your current zinc level as excessive consumption has a number of potential side effects.
High doses of zinc can reduce your body’s ability to absorb copper. This can lead to anaemia and weakening of the bones. It can also result in compromised immune health and reproductive function (just like a deficiency).
There are a number of dietary changes you can make to help maintain adequate zinc levels without supplementing.
- Avoid consuming phytate rich foods alongside zinc-rich foods. Phytates are compounds found in plant foods like cereal grains, legumes and nuts that inhibit zinc absorbtion.
- Choose protein sources that are rich in zinc. Foods like oysters, beef, lamb, chicken and pork are high in zinc but do not contain phytates. Furthermore, they also provide fat which improves zinc assimilation.
- Soaking, sprouting and fermenting grains can increase the bioavailability of zinc from these sources.
If you do choose to supplement zinc, ensure you keep monitoring your zinc levels to ensure you are not at risk of toxicity and choose a high quality supplement. Avoid those that are cut with calcium as this prevents absorption.
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