Zinc deficiency is quite common due to inadequate dietary intake and high sugar or alcohol consumption, poor soil quality and increased physiological demands. Studies have shown that zinc is required for the activity of more than 300 enzymes in the body. In fact, zinc is the second most abundantly distributed trace element in the body after iron.
Zinc is needed to maintain the integrity of the gut wall and to mobilise vitamin A from liver stores. It’s also required for the production of thyroxine by the thyroid and hydrochloric acid for digestion. It improves concentration, mood and sleep. It’s also required for blood sugar regulation, protein synthesis, tissue growth and wound healing. It is vital for the activity of many hormones and for a healthy immune system. It’s also an important factor in the metabolism of neurotransmitters and prostaglandins.
Symptoms of low zinc include:
- Retarded growth
- Poor appetite
- Loss or change of taste or smell
- Mental lethargy
- Sluggish digestion
- Slow wound healing
- Acne and other skin conditions
- Recurrent infections
- White spots on fingernails
- Stretch marks
- Excessive hair loss
- Stress, anxiety and depression
- Reduced sperm count and ejaculatory fluids
- Reduced sexual libido
There are various factors which can affect zinc bioavailability and absorption. These include:
- Existing zinc status of the individual - the lower the zinc levels, the greater the absorption of zinc.
- Excess sweating
- Dosage of zinc - as zinc dosages increased, the percentage of absorption actually decreases (due to saturation of the transport mechanisms)
- Zinc absorption increases with dietary protein intake
- Casein in milk and calcium inhibit absorption by binding with zinc ions
- Iron inhibits absorption of zinc as does high amounts of copper
- High cadmium levels inhibit absorption of zinc
- Phytates in cereals, corn and rice, inhibit absorption of zinc; the removal or reduction of phytate by enzyme treatment, precipitation methods, germination, fermentation or plant breeding significantly improves zinc absorption
Forms of Zinc Supplements
As you can see, absorption of zinc in the body is subject to so many variables. Your body does not naturally digest zinc easily. To make it more bioavailable, zinc needs to be disassociated into zinc ions and then attached to other molecules such as amino acids (proteins) that can transport the zinc into the cells of the small intestine. These transport proteins carry the zinc across the cell membrane into the portal circulation where it is delivered to the liver before being released into the circulation for distribution to all tissues. Some different forms of zinc include:
Zinc picolinate is combined with picolinic acid from the amino acid tryptophan to help to pass easier into your intestines for absorption. Studies have indicated that zinc picolinate is one of the better absorbed forms of zinc and is effective for the treatment and prevention of zinc deficiency. It is also commonly used for pregnant women.
Zinc glycinate is combined with a glycine molecule to enhance its absorption. Instead of competing with other minerals for absorption, the body recognises it as an amino acid and it enters the body via the amino acids channels. One study showed that the bioavailability of zinc glycinate was significantly superior by 16% to zinc sulphate, a commonly used form of zinc.8 It’s often combined with bioflavonoids (plant compounds) to reduce pain and swelling associated with osteoarthritis.
Zinc citrate is a water soluble form made by combining zinc with citric acid. One study found that zinc citrate, given as a supplement, is as well-absorbed as zinc gluconate but has a less bitter taste and thus increases compliance. It is the best type of zinc for use in toothpastes and mouthwashes to help prevent dental plaque and gingivitis and as a breath freshener.
Zinc gluconate is made by fermenting glucose, hence it has a long shelf life. It often comes in the form of a lozenge or is often used in nasal sprays. It is mostly used to treat the common cold and is easily absorbed by the body. One meta-analysis found that zinc gluconate lozenges were able to reduce cold duration by 28%. It is also used to speed up the healing of diaper rash in infants. Some zinc supplements contain the heavy metal cadmium as zinc and cadmium are chemically similar and often occur together in nature. Exposure to high levels of cadmium over a long time can lead to kidney failure. Zinc gluconate contains the lowest amount of cadmium levels of any zinc supplements.
Zinc acetate is formed by combining zinc with acetic acid. It is the best zinc supplement to treat the common cold. One study recommended using acetate lozenges within 24 hours of the onset of a cold for a three-fold increase in the rate of recovery. Zinc acetate is also used in treating Wilson’s disease which is a genetic disorder where copper builds up in the body. One report suggests that zinc acetate causes less dyspepsia (stomach upset) than the same amount of zinc sulphate.
Zinc methionine is attached to the amino acid methionine. This is another chelated form and is often found in over the counter lozenges to prevent colds or zinc deficiency.
Zinc sulfate Zinc sulfate is sometimes used in eye drops to ease irritation. It is also often taken orally to speed up wound healing. Zinc sulfate is the least expensive form but is the most likely to cause nausea and stomach upset as it competes with intestinal absorption of calcium.
Zinc oxide and zinc carbonate
The more insoluble zinc oxide and zinc carbonate are the least well absorbed of all of the different forms of zinc when given as a supplement without food. Zinc oxide is nonetheless used topically and internally. Topically, zinc oxide is used in sunscreens and formulas intended to improve skin issues such as diaper rash, eczema and psoriasis. Zinc carbonate is also often used for skin healing.