ZINC

Zinc has been known for its medicinal qualities over the ages, as ancient Greek medical texts mentioned that zinc oxide was used in ointments to heal wounds.  Zinc oxide is still today a common over-the-counter skin treatment.  Historically, it was reported in 1869 that zinc was essential for the growth of microorganisms, in 1926 zinc was recognized as a growth factor for plants, and in 1958 zinc was shown to be essential for the growth of poultry.  It was only in 1963 that human studies established for the first time that dietary zinc is essential for human health.

Zinc is one of the trace minerals that forms part of the micronutrients that our bodies need from our food to stay healthy.  Micronutrients refers to essential vitamins and minerals, which are chemical elements or substances that are required in trace amounts for normal growth and development.  Zinc is the second most abundant trace mineral in the body, next to iron.  Zinc is also an antioxidant, which helps prevent cell damage that contributes to various serious health conditions, such as heart disease. 

Zinc occurs in all cells throughout the body and the total amount of zinc in the body is approximately 1,5 gram in women and 2,5 gram in men, mostly stored in skeletal muscle and bone.  As the body doesn’t make zinc, it must be obtained from our diet and fortunately it is present in some food, added to others (those fortified with zinc), and in addition, available as a dietary supplement.

Functions of zinc in the body:

Although the body only needs zinc in small amounts, zinc is found in cells throughout the body and is involved in a wide range of different processes.  The following are a number of the major functions of zinc in the body:

• Growth and development:  Adequate zinc is required during times of rapid growth, such as pregnancy, childhood, and adolescence, as zinc plays a role in the growth and multiplying of cells.
• Immune function:  Zinc helps to make immune cells that fight germs.  Zinc plays an important role in enhancing immune function, as it supports the growth and normal functioning of immune cells and in this way helps to protect the body from viruses and bacteria.
• Cellular metabolism:  Metabolism encompasses the complex biochemical processes that keep us alive and is seen as the engine room of the body, which converts food (carbohydrates, protein end fat) into energy, building blocks, and waste products. Zinc has been compared to a workhorse in the body, as it supports over 300 enzymes to perform their vital functions, such as cell division, immune function, and wound healing.  It helps with the proper functioning of insulin and interacts in synergy with other minerals and vitamins.
• DNA:  A significant portion of cellular zinc is found in the cell nucleus, where it appears to be crucially involved in maintaining genetic stability, and in the process of gene expression.
• Building proteins:  After digesting a meal, dietary zinc is taken up by the cells in the body from the bloodstream.  Zinc binds to proteins in cells to support their structure and function and an estimated 10% of all proteins made in the cells need zinc to properly function.  However, much about these processes are still unknown and several aspects of how it supports cellular processes are not completely understood. 
• Reproduction:  Zinc supports reproduction as research has indicated that it improves sperm quality.  Evidence indicate that zinc plays a major role in the development from germ cells to sperm cells, in sperm cell maturation, sperm cell motility (the ability to move efficiently through the female reproductive system in order to fertilize an egg), and pre-fertilizer events in the female reproductive tract.
• Hormones:  Minerals, such as zinc, play a crucial role in maintaining hormone balance as well as supporting the functioning of the endocrine system.  Zinc in particular takes part in the production, secretion, and function of key hormones, which are associated with important endocrine glands such as the thyroid, pancreas, and productive organs.  For example, adequate zinc levels support the effective transmission of thyroid signals to regulate metabolism and other physiological processes.
• Nerve impulses:  One of the mysteries of neuroscience is how information is processed through the massive, interconnected circuits of neurons in the brain.  Scientists have fairly recently found that zinc ions are one of the signaling systems that neurons use, by releasing zinc from one cell which then binds to receptors on another cell, which is what a neurotransmitter does.  Research in this regard is ongoing.
• Colds:  Although zinc in the form of lozenges or syrup is deemed to reduce the severity and duration of cold symptoms, research has shown that zinc has little impact on the severity of cold symptoms but can reduce the duration by 2-3 days.
• Wound healing:  Zinc oxide lotions forms a protective barrier on the skin’s surface when applied to the skin and is a proven diaper rash treatment.  It also acts as a barrier to moisture, protecting the baby’s bottom from additional irritation.  It is also used to protect the skin against sunburn and to treat inflamed skin conditions such as burns, bedsores, and eczema. Apart from being used in topical creams to protect the skin, adequate levels of zinc are needed to create new cells, in particular collagen and fiber-like tissue.  Supplements can benefit people who are zinc deficient and have severe wounds or extensive burns.
• Diarrhea:  In many low-income countries there are high mortality rates among children with acute diarrhea.  Zinc is used to treat acute diarrhea due to its roles in supporting immunity and maintaining the mucosal integrity of the gastrointestinal system.  Clinical trials in low-income countries showed that zinc supplementation helps to shorten the duration of diarrhea in children.
• HIV:  As HIV infection reduces the absorption and metabolism of zinc from foods, HIV infected people may have low zinc levels in the bloodstream.  Research findings in this regard, however, were not conclusive.  In one study zinc supplementation reduced rates of immunological failure events but had no effect on mortality.  In more than one study zinc supplementation reduced the rates of diarrhea.  People with Aids often have diarrhea, resulting in excessive losses of zinc.  More research is needed to determine whether zinc supplementation may be beneficial for people with HIV.
• Eyesight:  Age-related macular degeneration is viewed as the leading cause of vision loss in older people.  Research has indicated that supplements containing zinc and antioxidants (such as beta-carotene, vitamin E, vitamin C, and copper) may delay the progression and vision loss associated with age-related macular degeneration, probably by preventing cellular damage in the retina.
• Sense of taste and smell:  Zinc is needed for the sense of smell and taste, as one of the enzymes crucial for proper taste and smell is dependent on zinc.  Zinc deficiency can reduce the sense of taste or smell.  On the other hand, studies found that the extended use of intranasal zinc, used to help treat a cold, has been linked to loss of the sense of smell, temporary in most cases.
• Diabetes:  As zinc levels are usually low in people with Type 2 diabetes, scientists suspect that zinc depletion may play a role in the progression of diabetes and that low levels of zinc may worsen the disease.  Zinc supplementation may lower blood sugar and high cholesterol in people with Type 2 diabetes.  International studies have indicated that the risk of Type 2 diabetes was 13% lower in participants with the highest zinc intakes, compared with those with the lowest intakes.  Supplementation reduced fasting glucose, fasting insulin, and insulin resistance.  However, scientists regard the evidence to date as insufficient to support any conclusions about the impact of zinc supplementation on the prevalence or severity of diabetes.

Sources of zinc:

The amin sources of zinc are from food and supplements.

Food sources: 

• Animal based foods are rich in zinc, such as meat, poultry, eggs, dairy, and seafood.  Beef and oysters in particular are rich in zinc.
• Certain plant foods such as legumes, nuts, seeds, beans, and whole grains also contain zinc.  However, the bioavailability of zinc from plant foods are lower as they also contain phytates, which can bind to zinc and lower its absorption.  Phytates are the storage form of phosphorus in plants that can bind some minerals such as zinc in the intestine, to form an insoluble substance that inhibits zinc absorption.
• With a varied diet the body usually gets enough zinc.

Supplements:

• Zinc supplements are available in pill and lozenge form.  It is important to determine zinc levels before supplementation, as excess zinc can interfere with the absorption of iron and copper, while high doses can cause headaches, nausea, and vomiting.  Zinc is also found in most multivitamin and mineral supplements.  Zinc supplements may contain zinc gluconate, zinc glycinate, zinc sulfate, or zinc acetate.

Other sources:

• Some denture adhesive creams contain zinc to enhance their adhesive properties and when use as directed is of no concern, but chronic, excessive use over years can lead to zinc toxicity, which may cause copper deficiency and neurological diseases.

How much zinc do we need?

According to Harvard and other sources, the recommended dietary allowance for adult 19 years and older is11 mg a day for men and 8 mg for women.  During pregnancy and lactation women require about 12 mg per day.  The tolerable upper intake, below which levels zinc is unlikely to have harmful effects on health, is 40 mg daily for adults.  Zinc toxicity would not normally occur from food, but from taking too many supplements.

*Adequate Intake (AI), equivalent to the mean intake of zinc in healthy, breastfed infants.

In many low-income countries the low intake of food rich in absorbable zinc, such as meat and fish, and a high intake of plant-based foods can result in zinc deficiency.  An estimated 17% of the World’s population has zinc deficiency.

Vegetarians and vegans may be zinc deficient due to the phytates in plant-based foods that inhibit the absorption of zinc.  They may benefit from certain food preparation techniques that reduce the binding of zinc by phytates and increase its bioavailability, such as soaking grains, beans, and seeds in water for several hours before cooking them.  Vegetarians and vegans may benefit from taking zinc supplements.

Conclusion:

At certain stages in life, zinc is a key mineral, and it is important to determine levels in the body, especially during periods of fast growth and development.  Zinc intake is important during pregnancy, infancy, and childhood as low levels can impair the growth of the baby and increase the risk of infections.  The fast growth period during adolescence also needs support from adequate zinc levels.   

Vegetarians and vegans need to consciously pay attention to zinc intake as they need higher amounts compared to people who include zinc rich meat and other animal proteins in their diet.

When in doubt or when having concerns about zinc levels due to health conditions, age, or dietary choices, a blood test is the most accurate way to determine zinc levels in the body.

References:

Zinc.  Published online and last reviewed March 2023.  Harvard T H Chan School of Public Health. Harvard Medical School.  (www.hsph.harvard.edu)

Zinc.  Fact Sheet for Health Professionals.  Published online and updated 28 September 2022.  Office of Dietary Supplements.  National Institutes of Health.  U.S. Department of Health and Human Sciences.  (www.ods.ad.nih.gov)

How zinc benefits your body – and how much zinc you need per day.  Published 29 January 2023.  Cleveland Clinic.  USA.  (A nonprofit multi-specialty medical centre that integrates clinical and hospital care with research and education.)  (www.clevelandclinic.org)

Zinc in diet.  Published online and reviewed 19 January 2023.  Medline Plus.  National Library of Medicine.  USA.  (www.medlineplus.gov)

Zinc.  Published 10 August 2023.  Mayo Clinic. USA.  (www.mayoclinic.org)

Zinc:  Food, functions, how much do you need, and more.  Published online and updated 11 January 2021.   European Food Information Council.  (www.eufic.org)

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