The importance of Zinc
Zinc (Zn) is a mineral needed for so many processes in the body that some researchers have questioned the use of the term trace element to describe it. Small amounts of Zn consumed daily is required to prevent deficiency however Zn is needed for so many functions in the body that deficiency can occur rapidly. Further depletion of Zn can occur during periods of illness and infection that can lead to prolonged illness and slow recovery. Interestingly Zn essentiality in humans has only been known about since 1961 whereas essentiality for plants and animals was known in 1869 and 1934 respectively.
What is zinc?
Zinc is an essential nutrient that is needed for optimal immune function, is a regulator of gene expression, a component of approximately 10% of proteins in the body, acts as an antioxidant and is so essential to the protection of every process within the human body that if we become deficient enough, our bodies break down lean muscle to keep Zn concentrations within our tissues from dropping. Zinc deficiency can result in delayed puberty and growth problems in children and can result in frequent infections, and skin problems including dry skin, acne, red blisters, and pustules.
Zinc is often described as a trace element. Although not needed in large amounts the term trace element is disagreed with by some researchers. Researchers from a 2018 paper stated ‘the concentration of cellular Zn is rather high such that Zn can hardly be considered a trace element and that Zn is used as a cofactor in proteins much more frequently than most vitamins’. Zinc might be a ‘trace’ mineral however it is so important that a body in a deficient state will increase the absorption of Zn from foods in an attempt to correct a deficiency.
What causes a Zn deficiency
The general causes of Zn deficiency include inadequate intake, increased requirements (stress, acute trauma, infection), malabsorption (Chron’s disease, Celiac disease), increased losses (chronic diarrhoea, persistent vomiting, diabetics, and alcoholics also lose Zn in their urine), and impaired utilization. Epidermal (skin), gastrointestinal, central nervous, immune, skeletal, and reproductive systems are the organs most affected clinically by Zn deficiency.
Zinc deficiency is a major factor in susceptibility to bacterial infections and can also lead to an exaggerated immune response to infections, leading to an increased risk of tissue damage. The first sign of a Zn deficiency is altered taste activity due to the role of salivary gustin (gustin=major Zn protein in human parotid saliva) in taste bud formation. Mild deficiency can result in impaired growth rate, suboptimal pregnancy outcomes and impaired immune responses, leading to poor wound healing and increased susceptibility to infection. Severe deficiency can result not only in growth impairment but also alopecia, diarrhoea, delayed sexual development and impotency, eye and skin lesions and impaired appetite.
Deficiency is more prevalent in diets high in cereals and low in animal foods. People on vegetarian and vegan diets often have low Zn status due to the lowered bio-availability of Zn from plant sources and the presence of phytic acid inhibiting the absorption of the Zn that is present. Phytic acid found in grains, seeds, nuts and legumes is the main known inhibitor of Zn.
Periods of growth put an increased demand on the body for Zn therefore pregnancy, childhood and adolescence are times where ensuring adequate levels of Zn is essential to prevent problems associated with deficiency. Zn intakes in the elderly are often inadequate due to reduced consumption of Zn rich foods such as red meat. There is also some evidence that the efficiency of Zn absorption may decrease with age.
Bioavailability
Bioavailability refers to the fraction of intake that can be absorbed into the blood system and used for physiologic functions of the body. For Zn, in healthy individuals, it is determined by three factors:
Individual's zinc status,
Total zinc content of the diet, and
Absorption rate of the zinc in the diet (higher from animal products, lower from vegetarian sources).
Absorption
Zinc absorption is largely determined by its solubility in the intestines which in turn is affected by the chemical form of Zn and the presence of specific inhibitors and enhancers of absorption. Zinc absorption is enhanced in response to low dietary intake or increased physiologic demand for example people who are Zn deficient absorb Zn more efficiently, whereas people on a high Zn diet show a reduced efficiency of absorption.
Excretion
Loss of Zn through the gastrointestinal tract accounts for approximately half of all Zn eliminated from the body. A considerable amount of Zn is secreted through biliary and intestinal secretions, but most of it is reabsorbed. This is an important process in the regulation of Zn balance. Other routes of Zn excretion include urine and surface losses (desquamated skin, hair, sweat).
Inhibitors
Phytic Acid
Various dietary factors can influence Zn absorption. Phytic acid found in grains, nuts, seeds, beans and legumes is the principal dietary factor known to limit Zn bioavailability by strongly binding Zn in the gastrointestinal tract. Soaking, sprouting and fermenting can reduce (not eliminate) the amount of phytic acid and improve absorption of Zn. However, as it is hard to know how much phytate is reduced when foods are prepared this way it is best to eat Zn containing foods away from phytate rich foods.
Iron
High doses of inorganic iron or non-heme iron found in plants and many supplements decreases Zn absorption. The effect of iron on Zn is exerted only at a very high ratio of iron to Zn and in situations where the iron is in solution or as a separate supplement rather than incorporated into a meal. The effects of iron also appear much less pronounced when Zn intake is optimal.
Enhancers
Proteins
Zinc absorption tends to increase with protein intake. Consumption of animal proteins (e.g., beef, eggs) improve the bioavailability of Zn from plant food sources possibly because amino acids released from the animal protein keep Zn in solution or the protein binds the phytate. The higher the diet is in animal products the greater the Zn absorption.
How much is too much?
High doses of Zn (50mg or more) can interfere with copper absorption, leading to low copper status (a bad thing). The adverse effect of excess Zn on copper metabolism has been identified as the critical effect on which to base the Upper Limit (The UL 40mg/day for adult men & women applies to total Zn intake from food, water and supplements including fortified food). Very high doses of Zn from supplements might also interfere with magnesium absorption and disrupt magnesium balance. Other adverse events associated with chronic intake of supplemental Zn include suppression of immune response and a decrease in high density lipoprotein (HDL) cholesterol (good cholesterol). The amount of Zn obtained from food is rarely as high as 50 mg, so the Zn in foods is unlikely to cause toxicity therefore it is best to get your Zn from food.
Foods high in zinc
The foods that are highest in Zn, providing approximately 12mg per 100g are oysters and beef liver. Wheat germ is also high in Zn at 12mg/100g however the presence of phytates here makes it less bioavailable. Other Zn rich foods include beef, lamb, and veal. There are few reliable vegetarian sources of Zn due to presence of phytates and low bio-availability.
People on keto or other high fat diets should be aware that fat displaces Zn. The fattier cuts of meat are lower in Zn than the leaner cuts. If you eat high fat, it is important to select Zn rich foods such as oysters and red meat, so that the fat does not displace the Zn from lower Zn foods you might be relying on.
There is no evidence of adverse effects from naturally occurring Zn in food.
Summary
Zinc is often only thought about in terms of immune function. We rush out to get Zn lozenges when we have a cold but an adequate level of Zn prior to getting sick is necessary for illness prevention, adequate wound healing, healthy pregnancies and better health in old age. People whose diets are low in animal products and/or have conditions that prevent Zn absorption or increase the need for Zn need to be mindful of the risks of Zn deficiency and take steps to ensure adequate Zn intake.
The information provided on this website is for information purposes only and is not meant to be nor should be considered medical advice.
