Zinc - a vital trace element
Information, effects, deficiency, dosage, side effects
Zinc plays an important role in a strong immune system and in energy production. It is also involved in the formation of thyroid and sex hormones, promotes muscle building, wound healing and prevents hair loss.
Zinc deficiency can lead to a drop in performance, reduced libido, and increased susceptibility to infections.
Zinc is one of the vital trace elements that must be supplied to the organism every day.
The trace element zinc is involved in numerous metabolic processes. For example, zinc plays an important role in the body's growth processes and in strengthening the immune system. It is also involved in the production of numerous enzymes.
After iron, zinc is the trace element that occurs most frequently in the body. In order to avoid zinc deficiency, it is important to ensure an adequate supply on a regular basis. For example, there is an increased need for zinc in athletes and pregnant or breastfeeding women.
Zinc has a lot of health benefits that it is almost impossible to describe them all here. Zinc is important for immunity, for reducing inflammation, to act as an antioxidant, cognitive function and much more!
Zinc is an essential mineral that is found in all organs, tissues, and fluids in the body.
As the second most common trace element in the body after iron, zinc plays a crucial role in a variety of biological processes. It plays a special role in energy production and in the formation of new tissue as well as building muscle. Zinc improves the skin and strengthens the bones, hair, and nails.
Zinc is necessary for the effect of more than 300 enzymes involved in the synthesis and metabolism of carbohydrates, fats, proteins, nucleic acids, and other micronutrients.
Zinc promotes wound healing and also has an anti-inflammatory effect. The positive effects of the mineral also include strengthening the immune system. It is indispensable for the formation of white blood cells and is found in the thyroid and sex hormones (e.g. testosterone) and insulin.
Zinc also plays a role in the stabilisation of cell and organ structures, immune function, cell division, growth, blood clotting, thyroid function, eyesight, taste, and smell.
Zinc is constantly consumed and requires regular food intake.
Because zinc plays such a critical role in the immune system, zinc deficiency contributes significantly to the global burden of diseases and is, therefore, an important public health problem.
The risk groups for zinc deficiency include people with digestive disorders, vegetarians, pregnant and lactating women, alcoholics and people with sickle cell disease.
Zinc is recommended for
- increased zinc requirement for competitive athletes
- one-sided or low-zinc diet (for example, only with a vegan or vegetarian diet)
- a weakened immune system or chronic and acute infections
- Skin problems (including allergies, acne, neurodermatitis)
- increased zinc losses, for example in connection with severe diarrhoea
- during pregnancy and while breastfeeding
Zinc in food
Good food sources for zinc include red meat, seafood (especially oysters), dairy products, nuts, legumes, and whole grains. However, zinc is more easily absorbed by the meat and other animal proteins.
Some cheeses are among the good zinc suppliers. In the area of plant-based foods, whole-grain cereals, oatmeal and legumes such as lentils or peas, for example, support the body's zinc supply. Most nuts are also considered to be rich in zinc.
Vegetables, cereals, and nuts are unfortunately not an ideal source because they contain phytate, a compound in plants that prevents zinc from being optimally absorbed.
Zinc deficiency and its consequences
There is no other substance that can replace zinc in the human organism. If an adequate supply is not regularly guaranteed, a zinc deficiency can occur. A moderate deficiency usually leads to unspecific systematic symptoms that often go undetected for a long time.
Possible symptoms of zinc deficiency include:
- Fatigue, lack of drive
- Lack of concentration, poor learning
- Increased susceptibility to infections and inflammation
- Bad wound healing
- Inflammatory skin changes
- Hair loss, thinning hair
- Brittle nails, white spots on the nails
- Impaired growth
- Decreased sexual interest
- Disorders of sensory perception
- Fungal infections
- Athlete's foot
- Mood swings
- Loss of weight and/or appetite
- Developmental disorders (in children)
- Growth disorders (in children)
- Rash and skin lesions
Sometimes even with a varied diet, the daily zinc requirement cannot be adequately covered. In normal cases, an amount of 9-10 mg is assumed for men, while women need about 7 mg of zinc per day.
The daily intake of zinc recommended by the German Nutrition Society (DGE) is age and weight dependent, with different guideline values for men and women.
The following guidelines are stated in milligrams (mg) per day:
- Infants up to 4 months: 1 mg
- Infants from 4 to 12 months: 2 mg
- Children from 1 to under 4 years: 3 mg
- Children from 4 to under 7 years: 5 mg
- Children from 7 to under 10 years: 7 mg
- Children from 10 to under 13 years: boys: 9 mg; Girls: 7 mg
- Children from 13 to under 15 years: boys: 9.5 mg; Girls: 7 mg
- Adolescents from 15 years and adults: Men: 10 mg; Women: 7 mg
- Pregnant women starting at the 4th month: 10 mg
- Breastfeeding: 11 mg
For people with a zinc deficiency or an increased zinc requirement, dietary supplements in the form of zinc tablets or zinc capsules can provide useful support for the supply of zinc to the human body.
Zinc side effects and overdose
Zinc is one of the metals and can be toxic in large amounts. The recommended maximum zinc intake is 40 mg for adults. Possible signs of acute zinc poisoning include nausea and vomiting, loss of appetite, diarrhoea, abdominal cramps and headache.
Chronic zinc overdose (from 150 mg/day) can lead to changes in the iron or copper deposits in the body, as well as to an impairment of the immune system. The recommended maximum amount of zinc should therefore not be exceeded.
For whom is zinc particularly important?
- People with a zinc deficiency
- People with skin problems
- Pregnant and breastfeeding women
- People with a weakened immune system
- People who have an increased need for zinc due to taking medication
- Vegans and vegetarians
Zinc and the immune system
Zinc is essential for the normal development and function of many immune cells. Because of the critical role zinc plays in the immune system, even mild zinc deficiency can affect immune function and increase the risk of bacterial, viral, and parasitic infection.
In clinical conditions associated with immunodeficiency (e.g. sickle cell disease, human immunodeficiency virus (HIV) infection, down syndrome, and for elderly patients), zinc supplements can restore the natural killer cell activity, lymphocyte production, and infection resistance.
Studies of HIV patients with low zinc levels in the blood show that a permanent zinc supplement is associated with lower opportunistic infections and a reduced risk of immunological failure. However, the supplement must be exercised with caution, as excessive zinc can worsen the symptoms of the disease.
People with acrodermatitis enteropathica (hereditary zinc deficiency syndrome, a genetic disorder that affects zinc absorption) experience high infection rates. Supplementation with zinc in therapeutic doses leads to a complete recovery.
Many studies have shown that a zinc administration reduced the duration, severity, and frequency of acute and chronic diarrhoea, acute lower respiratory infection, and malaria for infants and children in developing countries.
Similar beneficial effects have been reported for other infectious diseases in humans including shigellosis (bacterial dysentery), leprosy, tuberculosis, leishmaniasis, hepatitis C and the common cold (by increasing Th1 cytokines).
On the other hand, excessive zinc levels can suppress immunity. A study of healthy young men showed that high doses of zinc reduced multiple immune functions, including lymphocyte activation and neutrophil phagocytosis
Zinc acts as an antioxidant
A study in the elderly showed that zinc supplementation could reduce fat peroxides in the blood.
In another study, zinc reduced DNA breaches in women. DNA breaches are commonly used as a parametric marker to determine the amount of injury induced by oxidative stress.
Zinc was also able to restore the superoxide radical scavengers to normal levels in men with asthenospermia (poor sperm motility).
In addition, zinc has protected mice against radiation-induced oxidative stress.
Zinc supplementation has also shown efficacy in the treatment of Wilson's disease, a disorder in which copper accumulates in tissue.
Zinc also helps prevent skin cell death from oxidative stress and bacterial toxins.
Zinc and inflammation
Zinc inhibits the production of many inflammatory cytokines by inhibiting NF-kB.
Studies in the elderly (who often suffer from zinc deficiency) show that zinc suppresses inflammation by lowering cytokines and other inflammatory markers.
Zinc also shows effectiveness in a variety of inflammatory conditions, including irritable bowel syndrome, acne, and asthma.
In an aged mouse model, zinc supplementation resulted in less age-related increases in inflammatory markers.
Zinc and autoimmune reactions
Many studies have shown that zinc can suppress unwanted immune reactions (e.g. autoimmunity and graft rejection) by inducing regulatory T-cells.
A study in healthy men found that zinc can reduce the rate of graft rejection while protecting the body from infections resulting from a suppressed immune system.
In mouse models with multiple sclerosis and arthritis, zinc improved the symptoms of the disease by reducing inflammation, suppressing T-cell proliferation and increasing regulatory T-cells.
In mixed lymphocyte cultures, zinc-induced regulatory T-cells helped reduce graft rejection by decreasing inflammatory cytokines and T-cell proliferation.
Similarly, zinc reduced heart transplant rejection in the mouse models by preventing graft tissue death (by inhibiting caspase-3).
Positive changes in joint swelling, morning stiffness and walking time after zinc therapy were observed in patients with rheumatoid arthritis.
Zinc for allergy and asthma
In response to grass pollen, an allergen that is a major cause of allergic rhinitis in many parts of the world, zinc raised regulatory T-cells and decreased proliferation in peripheral blood mononuclear cells (PBMCs) isolated from allergic subjects.
Low blood zinc levels are associated with more severe asthma symptoms in children.
One study showed that zinc supplementation improved symptoms (e.g. coughing, wheezing and shortness of breath) in children with asthma.
Zinc was also able to reduce airway inflammation and hyper-reactivity in mouse models of allergic inflammation and asthma.
In allergen-sensitive mice, zinc was able to inhibit epithelial cell death in the respiratory tract (by inhibiting caspase-3).
Zinc and the wound healing
Zinc improved the repair of skin ulcers in diabetics. A zinc deficiency is also associated with delayed wound healing.
Animal and human studies show that zinc administration can speed up the healing process after surgery, burns, and other wounds.
When applied topically, zinc oxide improved the healing of excisional wounds in rats.
Zinc for mental function
Zinc supplementation has been shown to improve cognitive recovery in zinc-deficient people who have experienced an ischemic stroke.
A double-blind study in children found that zinc supplements resulted in superior neuro-psychological performance, particularly attention and reasoning skills compared to controls.
A randomised study showed that supplementation with zinc led to increased activity, intellectual development and motor quality in infants and young children.
In older Alzheimer's patients, zinc therapy protected against cognitive decline by lowering the free copper levels in the blood that are toxic to the brain.
Many animal studies show that zinc in moderate concentrations is neuroprotective and helps maintain learning and memory functions.
In a mouse model with Alzheimer's disease, zinc supplements reduced the pathological factors associated with disease progression (e.g. ÿ-amyloid and tau protein loads) and improved mitochondrial function and growth factor BDNF (brain-derived neurotrophic factor) in the hippocampus.
Another study showed that maternal zinc supplementation enhanced spatial learning and memory in rat puppies.
One study found that moderate doses of zinc (12 mg/kg) prolonged survival in an ALS mouse model prolonged.
Zinc and psychiatric disorders
A study in OCD patients showed that the addition of zinc to fluoxetine therapy was able to reduce symptoms (as assessed by the Yale-Brown Obsessive-Compulsive Scale). Since zinc can suppress the release of glutamate and transmission, it may have improved OCD symptoms.
One study found that when combined with methylphenidate (a CNS stimulant), zinc supplementation reduced hyperactivity and impulsiveness in children with ADHD.
A study in schizophrenic men found that zinc in combination with risperidone improved many symptoms associated with this disorder (e.g. aggression, hallucinations, and delusions). This effect is partly attributed to the antioxidant and antidepressant properties of zinc.
Zinc and autism
One study found that autistic people have lower zinc levels compared to non-autistic people. In the study, the severity of autistic symptoms (e.g. consciousness, hyperactivity, recipient language, focus and attention, eye contact, sneaking, sensitivity to sound, tactile sensitivity, and seizures) decreased after treatment with zinc and vitamin B6.
Studies found that prenatal zinc treatment prevented autistic-like behaviours (e.g. induced social deficits, repetitive behaviours, and cognitive inflexibility) in the offspring of rats, suggesting a possible link between zinc deficiency and autism development.
A recent study found that zinc reverses brain cell changes due to autism: "Our work shows that even cells that carry genetic changes associated with autism can respond to zinc."
"Our research focuses on the Shank3 protein, which was located in synapses in the brain and is associated with neurodevelopmental disorders such as autism and schizophrenia." "Human patients with genetic changes in Shank3 show profound communication and behavioural deficits. In this study, we show that Shank3 is a key component of a zinc sensitive signaling system that regulates how brain cells communicate. ”
“It's fascinating how autism-related changes in the Shank3 gene affect brain cell communication,” says Dr. Montgomery. "These genetic changes in Shank3 do not change the ability to respond to zinc."
"As a result, we showed that zinc can increase brain cell communication that was previously weakened by autism-related changes in Shank3."
"Disorders of the regulation of zinc in the body can not only affect how synapses work in the brain, but it can also lead to cognitive and behavioural disorders in patients with psychiatric disorders."
"Together with our results, the data suggest that environmental / nutritional factors such as changes in zinc content can alter the signaling system of this protein and reduce its ability to regulate nerve cell function in the brain," she says.
Zinc for stress and mood
Zinc supplementation has shown efficacy in the treatment of mood disorders (e.g. depression and anxiety) clinically and in animal models.
Zinc also increases brain-derived neurotrophic factor (BDNF) levels, which are low in people with depression. One study found that zinc therapy was able to improve overall mood in overweight test subjects, possibly by increasing BDNF levels.
Zinc controls cell death
Both high and low intracellular concentrations of zinc trigger apoptosis (a form of programmed cell death) in many cell types.
Zinc deficiency and cancer
Zinc deficiency significantly increases the risk of cancer in the mouth, esophagus, and stomach. The digestive tract tissue is more susceptible due to the high exposure to external toxins.
Low blood zinc levels are also associated with the head, neck, lungs, gall bladder, prostate, and ovarian cancer. Restoring zinc levels can improve natural killer cell functions, which is essential for killing tumor cells.
Zinc can also block tumor growth by reducing glucose uptake, preventing new blood vessels from growing, and inducing cell death in cancer cells in animals and humans.
Zinc is antimicrobial
In high doses, zinc inhibits the growth of several types of bacteria, especially gram-positive organisms.
Zinc showed antibacterial activity against aerobic and anaerobic organisms in root canals.
Zinc also inhibited the accumulation and growth of staphylococcus aureus (S.aureus) in the skin tissue.
Zinc also shows antimicrobial effects against the usual wound flora in rats.
Zinc and epilepsy
Several studies have reported a significant decrease in zinc levels in the blood of patients with persistent epilepsy.
A study in epileptic children showed that zinc therapy significantly reduced the frequency of attacks in 31% of the treated children.
Zinc supplementation could also increase the latency (a period between seizures) of febrile seizures in rats.
Zinc promotes growth
In a number of studies, supplementing with zinc showed significant positive effects in height and weight measurement in children, especially in underweight children and children with stunted growth.
Analysis of the studies of growth in children showed that a dose of 10 mg zinc daily for 24 weeks resulted in a net increase of approximately 0.37 cm (in size) in children who received a zinc supplement compared to children who were treated with a placebo.
Zinc also increases muscle mass in children.
Zinc and the gut
Zinc supplementation has a protective effect on the intestinal mucosa of animal models and humans in a variety of gastrointestinal diseases (e.g. inflammatory bowel diseases, alcohol toxicity, and colitis).
Zinc stabilised the intestinal mucosa and reduced gastric and small intestine injuries by improving the intestinal repair processes in rats and mice.
Zinc also protected the intestinal mucosa from alcohol-related damage in rats and mice.
Zinc can prevent intestinal permeability, which can reduce the risk of inflammatory bowel disease.
A study in patients with dyspepsia (indigestion) found that inflammation in H.pylori induced gastric cancer was negatively correlated with zinc concentration, suggesting that zinc may reduce the risk of gastric cancer by suppressing gastric inflammation.
Zinc and sleep quality
Women and children with higher blood-zinc concentrations have better sleep quality. A study in infants showed that zinc supplementation could increase the length of sleep.
Zinc promotes appetite
One of the earliest signs of zinc deficiency is a loss of appetite.
A study in rats showed that oral zinc supplementation was able to dramatically stimulate food intake (by increasing orexin and neuropeptide y).
Clinical studies in patients with anorexia nervosa (AN) show an essential link between the disease and low zinc levels in the blood.
Many studies with oral supplementation with zinc reported an increase in weight gain, muscle mass, appetite, taste sensitivity, and food intake in AN patients.
Zinc and skin health
Zinc has been shown to be beneficial for a variety of skin conditions (e.g. acne, warts, rosacea, eczema, psoriasis, melisma, and dandruff).
In people with acne vulgaris, groups who received zinc as a dietary supplement showed a significant improvement in symptoms compared to placebo groups.
Clinical studies in patients with viral warts led to complete diagnosis of warts for a majority of the people treated with zinc.
Zinc shows similar efficacy in the treatment of genital herpes (genital warts caused by herpes simplex virus (HSV) 1 and 2).
A study in people with rosacea (a chronic inflammatory disease characterised by blushing, small blood vessels and red bumps on the face) showed that oral zinc was able to reduce the symptoms of the disease.
Zinc supplementation is similarly effective in treating other inflammatory skin conditions such as psoriasis and eczema, probably due to zinc's anti-inflammatory and antioxidant properties.
Zinc can also treat seborrheic eczema (dandruff). Studies show that shampoos containing zinc can significantly reduce the scaling and inflammation associated with dandruff.
Melasma is a skin pigment disorder that causes discoloration of the brown skin. Zinc treatment was able to reduce the severity of this disease in affected patients with minimal side effects.
Zinc also protects against sun damage to the skin, which can cause skin ageing and cancer. A human study found that oral zinc supplementation was better than titanium oxide for protection against UV radiation.
Zinc and hair loss
In a clinical study, topical zinc improved hair growth in bald men. It has been suggested that zinc's antimicrobial, anti-inflammatory, antioxidant and anti-androgenic effects on the scalp could potentially contribute to the strength of hair density.
Another study in women with the polycystic ovarian syndrome (PCOS) showed that zinc supplementation had positive effects on a number of symptoms, including alopecia (hair loss).
Zinc treatment also reversed hair loss in patients who have undergone vertical gastroplasty (gastric stapling), a surgical operation that can lead to zinc deficiency.
Zinc protects the liver
Zinc supplementation in animal models of alcoholic liver disease (ALD) protected the liver by blocking most mechanisms of liver injury (e.g. intestinal permeability, endotoxemia, oxidative stress, excess inflammatory cytokine production, and liver cell death).
In patients with non-alcoholic cirrhosis, zinc supplementation improved liver function and prevented excessive copper accumulation, which can damage the liver (R). Zinc also improved the outcome of patients with hepatitis C, which, if left untreated, can lead to liver scars.
Zinc for strong bones
Studies have found that zinc can increase bone density and strength by increasing bone formation and preventing bone loss.
Zinc treatment stimulated bone formation activity in osteoblast cells (bone-forming cells) in mice.
Another study showed that supplementation with zinc increased the bone formation markers (e.g. ALP, BAPE and BAP-M) in healthy men.
Zinc was also able to suppress bone fracture activity in mouse bone marrow cultures by inhibiting bone fracture markers (e.g. parathyroid hormone and PGE2).
Due to its bone-strengthening effects, zinc has been shown to protect against many bone-related complications in animals and humans.
Zinc and the heart
Studies have shown that zinc levels are often low in people with arteriosclerosis (hardening of the arteries), heart disease, chest pain, and heart attack.
One study found that a higher rate of heart failure was associated with zinc deficiency.
Other studies showed that high doses of zinc were able to prevent and treat angina (chest pain) in patients with atherosclerosis.
Supplementary zinc was also able to protect the heart from stroke injuries in rats and mice.
Zinc and diabetes
Zinc ions can bind to insulin receptors and activate insulin signaling pathways.
By mimicking insulin, zinc reduces excessive insulin secretion by pancreatic cells, which protect the pancreatic tissue from damage.
Zinc also improves the solubility of insulin in pancreatic cells and increases insulin binding to its receptor.
Because of the essential role of zinc in the processing, storage, and secretion of insulin, a deficiency can lead to increased insulin resistance.
One study found that prediabetic patients are more likely to suffer from zinc deficiency.
Other studies found high percentages of zinc deficiency in type 2 diabetes patients.
Studies in women report that higher dietary zinc intakes can reduce the risk of developing type 2 diabetes.
Several studies found that zinc supplementation lowered fasting blood sugar levels and improved insulin sensitivity in diabetic animal models and humans.
Zinc also reduced the severity of diabetic neuropathy (nerve pain), oxidative stress and cholesterol / triglyceride levels in type 2 diabetics.
Zinc and diet
Leptin is a hormone that plays a role in appetite and weight control. Zinc restriction can lead to decreased leptin production from fat cells in rats and humans.
Restoration of zinc levels in men with marginal zinc deficiency led to an increase in blood leptin levels (possibly due to increased IL-2 and TNF-alpha).
Zinc and male fertility
The seminal zinc concentration is positively correlated with sperm count, motility, and viability. This is probably because of the role zinc plays in stabilising cell membranes and DNA (by reducing oxidative damage) to sperm and enhancing spermatogenesis (new sperm formation).
Low to moderate doses (12-120 mg/kg) of zinc intake appeared to improve reproductive function in rats.
Zinc is highly concentrated in the prostate and testes and is involved in the synthesis of testosterone.
In infertile men (with low blood testosterone), additional zinc led to an increase in sperm count, testosterone, dihydrotestosterone (DHT), and fertility.
The testosterone-boosting effect of zinc could help increase libido and sexual performance in men with erectile dysfunction, who often have low testosterone levels.
Zinc can also reduce oxidative damage to the testicles. In rats, zinc was able to maintain testicular function (measured by testicular weight, sperm concentration, and testosterone level) in response to oxidative stress induced by cigarette smoke.
Zinc on fatigue
Low levels of zinc in the blood are associated with many symptoms of chronic fatigue syndrome (e.g. fatigue, depression, and difficulty concentrating).
One study found that blood zinc levels were significantly lower in patients with chronic fatigue syndrome (CFS) than in normal controls and that the symptom severity was negatively correlated with zinc levels. The study concluded that zinc may be effective in alleviating CFS symptoms due to its antioxidant and anti-inflammatory properties.
Intestinal inflammation (caused by a leaky gut) is common for people with CFS.
One study found that treating leaky intestines with a mixture of anti-inflammatory and antioxidant substances including zinc led to a significant improvement in symptoms in CFS patients.
Zinc and athletic performance
A study by wrestlers found that heavy training can significantly reduce thyroid hormones and testosterone levels, which can lead to fatigue. However, supplementing with zinc was able to prevent this loss, which suggests that zinc intake (in physiological doses) can improve athletic performance. Another study of sedentary men showed similar results.
Zinc and blood clotting
Human studies show that zinc is part of the regulation of prothrombotic (blood clot formation) and anti-thrombotic (blood clot prevention) factors that are derived from platelets and the blood vessel lumen.
Hyperzincemia (high levels of zinc in the blood) can cause blood clotting during hypocincemia hypocalcemia (low levels of zinc in the blood) to increase blood clotting times. Both conditions affect platelet aggregation and abnormal bleeding.
A study found that restoring zinc levels in zinc-deficient men led to normalised platelet aggregation and blood clotting time.
Zinc in pregnancy
Low blood zinc levels are associated with pregnancy complications (e.g. spontaneous abortion, pre-eclampsia, extensive pregnancy, premature birth, and abnormal fetal development).
Studies have shown that maternal supplementation with zinc (for zinc deficiency or underweight women) can reduce the risk of premature birth and protect against fetal damage from exposure to alcohol.
A study found that Indian mothers who received additional zinc had longer pregnancy times and babies with healthier weights.
Another study in pregnant women (with low zinc levels in the blood) found that supplementation with zinc (25 mg/day) significantly increased the birth weights of the infants and the head circumference during the second half of pregnancy.
It is suggested that these positive effects are a result of zinc's ability to inhibit embryonic cell death, increase growth factors (e.g. IGF, PDGF and FGF) and reduce oxidative damage, all of which contribute to healthy fetal health and to promote development.
Zinc and women's health
Zinc deficiency is associated with hormonal imbalances, which can lead to problems with ovarian function, menstrual irregularities, and infertility.
Several studies have found that this oral administration of zinc (in combination with mefenamic acid and alone) could reduce the severity and duration of menstrual pain in women.
These effects are probably due to the inhibition of prostaglandin metabolism in the uterus by zinc, which leads to reduced painful cramps in the lower abdomen.
In women with polycystic ovary syndrome (PCOS), insulin resistance can lead to increased production of androgen hormones (e.g. testosterone and DHEA), which can lead to balding, body hair growth, irregular periods, and infertility.
Studies have found that zinc supplementation in women with PCOS can lower insulin levels and improve symptoms of the disease (e.g. body hair growth and baldness).
Women with endometriosis (a condition in which the inner tissue of the uterus grows outside the uterus) showed low levels of zinc in the blood.
One study reported that the intake of antioxidants (such as vitamin C, vitamin E, selenium and zinc) was inversely correlated with the severity of endometriosis progression in women, suggesting that zinc can slow the development of this disorder.
Zinc for pain
Zinc has shown pain-relieving properties in a number of animal studies.
In rats with sciatic nerve injuries, the injection of zinc chloride has significantly alleviated thermal hyperalgesia (increased sensitivity to pain) in a dose-dependent manner.
Another study showed that zinc salts were able to suppress pain in mice that were exposed to a range of painful stimuli (e.g. heat and irritating chemicals).
Zinc reduced the frequency and severity of muscle cramps in patients with chronic liver disease.  It is suggested that zinc partially relieves pain by binding to the NMDA receptor (as an antagonist), which is involved in the initiation of pain pathways.
Zinc for the taste sensation
Zinc deficiency is associated with decreased taste sensitivity.
This may be due to the fact that gustin (or carboxylic acid anhydrase VI), a zinc-dependent enzyme, is not as active when the concentrations of zinc are low in the saliva.
A study found that supplementation with zinc led to an increased taste intensity (as judged by salt approval thresholds) in Indian adolescents (who often suffer from zinc deficiency).
Zinc for hearing disorders
Zinc deficiency is associated with impaired hearing in mice and rats, which can be cured with zinc supplementation.
This is probably a result of the protective effect of zinc (by increasing SOD) against toxins in the ear structures (e.g. cochlea and vestibule).
People with tinnitus (ringing in the ears) have lower zinc levels in the blood.
One study reported that zinc supplementation (50 mg/day) for two months was able to reduce the severity of tinnitus in 82% of patients.
Another study found that adding zinc to oral corticosterone was associated with a greater improvement in symptoms in people with sudden sensorineural hearing loss (sudden deafness for unknown reasons) than with corticosterone alone.
Otitis media (OM) is an infection of the middle ear. A study found that zinc supplementation could significantly reduce the rate of otitis media in healthy children from low-income areas.
Zinc and the lifespan
Oxidative stress is believed to accelerate the ageing process. Zinc is a key component of Cu/Zn superoxide dismutase (Cu/Zn SOD), a powerful enzyme that neutralises superoxide radicals.
One study found that worms (e.g. s. cerevisiae) and mice that were genetically engineered to express high levels of SOD had longer lifespans.
Mutations in the SOD gene are associated with many age-related diseases (e.g. ALS, Parkinson's disease, Alzheimer's disease, and cancer).
Inflammation is also involved in the ageing process.
Zinc supplements in the elderly have been shown to reduce inflammation, oxidative stress, and the rate of infection.
Zinc, due to its antioxidant and anti-inflammatory properties, can promote longevity, especially in the elderly, who often suffer from zinc deficiency.
Zinc and the thyroid glands
In animal and human studies, zinc deficiency is associated with a decrease in thyroid function (due to the low levels of triiodothyronine (T3) and free thyroxine (FT4) in the blood).
Supplementation with zinc has shown effective effects on thyroid function in humans.
In disabled hypothyroid patients receiving anticonvulsant therapy (with mild to moderate zinc deficiency), supplementing with zinc was able to normalise the thyroid hormone levels in the blood (e.g. T3 and FT3) and restore thyroid function.
In a case study by two university students, zinc intake increased thyroid hormone levels (e.g. T3 and T4) and residual metabolism. Zinc supplementation also appeared to reverse the deleterious effects of radiation emitted by computer monitors on computer users' thyroid hormone levels.
Zinc and chemotherapy
Mucositis (ulceration of the mucous membranes) is a common side effect of chemotherapy and radiation therapy.
Studies in patients who have undergone chemotherapy and radiation therapy showed that taking zinc reduces the severity of oral mucositis. Dysgeusia (distortion of taste) and dysosmia (distortion of smell) can also occur during chemotherapy.
One study found that taking 100mg of zinc daily for 4-6 months improved the symptoms of dysgeusia and dysosmia in patients with carbon dioxide deficiency VI (Gustin).
Zinc is known to stimulate the production of carbonic anhydrase VI, an enzyme in the saliva that is involved in the growth of the taste buds.
Zinc and the metabolic syndrome
Metabolic syndrome is a group of conditions (e.g. obesity, insulin resistance, high blood pressure, and high cholesterol) that can lead to an increased risk of developing heart diseases and type 2 diabetes.
A study in children with metabolic syndrome found that zinc supplementation reduced insulin resistance, oxidative stress, inflammation, blood sugar, cholesterol, and the body mass index.
Zinc and eye health
Age-related macular degeneration, a major cause of blindness in the elderly, is believed to be caused by oxidative stress. Clinical studies have found that zinc supplementation can slow the progression of the disease, possibly by preventing oxidative damage to the retina.
Zinc has been suggested to protect against diabetic retinopathy (which can lead to blindness) by preventing retinal capillary cell death and neovascularisation (new blood vessel growth). This is due to the ability of zinc to reduce oxidative stress and inflammation (by inhibiting NADPH oxidase and NF-ÿB), which is involved in the progression of diabetic retinopathy.
Night blindness is one of the earliest symptoms of vitamin A deficiency. A study found that zinc was able to improve the effects of vitamin A in restoring night vision in pregnant women (with a low zinc content).
Zinc and the mitochondrial function
A study in rats found that zinc absorption increased the electron transfer system and the oxidative phosphorylation in the liver mitochondria, which increased the energy production (ATP) in liver cells.
Zinc and body odour
Bromhidrosis (body odour) is usually associated with an increased bacterial flora in the armpit, which mainly consists of Staphylococcus and Corynebacterium species.
Due to its antibacterial effect, topical zinc has been shown to be effective in reducing armpit and foot odour in clinical studies.
Zinc and oral health
Zinc deficiency can lead to excessive plaque formation and worsen the inflammatory process in gum disease (from increased production of IL-1).
Zinc-based mouthwashes have been found to be effective in reducing plaque growth.
At the same time, a study in children from areas with low income found that a daily intake of 15 mg zinc for ten weeks was associated with reduced plaque formation on the teeth.
Zinc and cystic fibrosis
Mucoviscidosis, or cystic fibrosis, is a genetic disorder that can cause difficulty breathing, pneumonia, and an inability to gain weight. A retrospective study in patients with cystic fibrosis showed that supplementing with zinc could improve lung function and energy intake and reduce the infection rate.
Zinc in arsenic poisoning
A study in patients with chronic arsenic poisoning showed that zinc in combination with spirulina extract was effective in reducing symptoms (e.g. melanosis and keratosis).
Zinc and opioid addiction
Opioid users have lower zinc levels.
Studies in mice and rats found that zinc reduced the dependency intensity of morphine (an opioid), while zinc chelates exacerbated the withdrawal symptoms.
Based on these results, a literature review article suggested that zinc supplementation is beneficial in reducing the risk of addiction in people taking opioids for chronic pain due to the pain-relieving effects and low toxicity of zinc.
What experts say about zinc:
1. Zinc to prevent colds
The evaluation of various studies by researchers from the Cochrane Collaboration, an international network, has shown that zinc can not only support regeneration in acute infections, but it can also be used preventively.
With a regular intake over several months, schoolchildren were less likely to catch a cold compared to their peers of the same age, had less absenteeism and did not take antibiotics as often.
2. Zinc for prostate health
Studies in France and Sweden have shown that an adequate supply of zinc - in combination with selenium - can significantly reduce the risk of prostate cancer. Zinc can also be used sensibly as an accompanying measure for prostate diseases.