Zinc is one of those minerals that gets mentioned often but rarely explained well. It’s the second most abundant trace element in the human body after iron, yet many people have no idea what it actually does or whether they’re getting enough.

I’ve seen zinc marketed as everything from a cold remedy to a testosterone booster to an acne cure. Some of these claims hold up under scrutiny; others fall apart completely when you look at the research. In this article, I’ll walk through what the evidence actually says about zinc supplementation, including where it genuinely helps and where the hype outpaces the science.

What Is Zinc and Why Does It Matter?

Zinc functions as a cofactor for over 300 enzymes in the body. It’s involved in DNA synthesis, cell division, wound healing, immune function, and the metabolism of proteins, fats, and carbohydrates. Without adequate zinc, none of these processes work properly.

Your body contains roughly 2 to 3 grams of zinc total. About 90% sits in your muscles and bones, with the rest distributed across organs including the prostate, liver, kidneys, brain, and pancreas 1.

Unlike iron or calcium, zinc doesn’t have a dedicated storage system in the body. This means you need a consistent daily intake to maintain adequate levels, whether from food or supplements.

Signs of Zinc Deficiency

Normal blood zinc levels in adults range from 70 to 250 μg/dL. Mild deficiency occurs when levels drop to 50-60 μg/dL, while severe deficiency is anything below 50 μg/dL.

Mild to moderate deficiency symptoms may include:

Loss of appetite and changes in taste perception
Delayed wound healing
Increased susceptibility to infections
Rough or dry skin
Hair thinning
Mental fatigue and difficulty concentrating
Delayed growth in children

Severe deficiency symptoms may include:

Significant hair loss
Skin lesions and dermatitis
Chronic diarrhoea
Impaired night vision
Hypogonadism (reduced testosterone) in men
Mood disturbances

The World Health Organisation estimates that zinc deficiency affects over 2 billion people globally, predominantly in developing countries where diets rely heavily on plant-based foods with poor zinc bioavailability 2.

Blood tests for zinc aren’t always reliable because most zinc is stored inside cells rather than circulating freely. If you suspect deficiency, discussing symptoms with your doctor is often more informative than the blood test alone.

Who Is at Risk of Zinc Deficiency?

Certain groups are more likely to have inadequate zinc intake or absorption:

Vegetarians and vegans – plant-based zinc sources have lower bioavailability, and phytates in grains and legumes can inhibit absorption
People with inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis
Those with chronic kidney disease, particularly on dialysis
Pregnant and breastfeeding women – requirements increase significantly
Older adults – absorption tends to decline with age
Heavy alcohol users – alcohol reduces zinc absorption and increases urinary excretion
People taking certain medications including diuretics and penicillamine

What Are the Evidence-Based Benefits of Zinc?

1. Immune Function

Zinc plays a central role in both innate and adaptive immunity. It’s needed for the development and function of immune cells including neutrophils, natural killer cells, and T lymphocytes.

A systematic review of 35 randomised controlled trials found that zinc supplementation significantly reduced markers of inflammation including C-reactive protein, TNF-α, and IL-6, while increasing T cell counts 3. The effects were most pronounced in people who were already zinc-deficient or dealing with illness.

My take: If your zinc status is adequate, supplementing more won’t necessarily boost your immunity further. But if you’re deficient, correcting that deficiency does appear to have meaningful benefits.

2. Common Cold Recovery

This is probably zinc’s most well-known use, and the evidence is reasonably solid. Zinc lozenges appear to reduce cold duration when taken within 24 hours of symptom onset.

A meta-analysis of three randomised trials found that people taking zinc lozenges (80-92 mg daily) recovered about three times faster than those taking placebo 4. The proposed mechanism involves zinc’s ability to block viral replication in the throat.

Worth noting: The form matters. Zinc lozenges work because they deliver zinc directly to the throat where cold viruses replicate. Zinc tablets swallowed whole are unlikely to have the same effect. Also, the doses used in these studies are higher than standard supplement doses and shouldn’t be continued long-term.

3. Blood Sugar Regulation

Multiple studies suggest zinc supplementation may help with glucose control, particularly in people with diabetic bladder dysfunction or type 2 diabetes.

A meta-analysis of 32 trials involving 1,700 participants found significant reductions in fasting blood glucose, post-meal glucose, fasting insulin, and HbA1c in those taking zinc supplements 5. The benefits were most apparent in people with established diabetes using inorganic zinc forms.

The catch: These improvements, while statistically significant, were modest. Zinc supplementation isn’t a replacement for diabetes medications or lifestyle changes, but it might provide additional support for some people.

4. Male Fertility

Zinc is highly concentrated in the prostate gland and plays a role in sperm production and testosterone metabolism. This has led to significant interest in zinc for male fertility.

A systematic review found that infertile men had significantly lower seminal plasma zinc levels than fertile controls. Zinc supplementation appeared to improve sperm volume, motility, and morphology 6.

Reality check: These findings are promising but come from relatively small studies. Zinc isn’t a magic fertility fix, but ensuring adequate intake seems sensible for men trying to conceive.

5. Acne Treatment

Zinc has anti-inflammatory and antibacterial properties that may help with acne. A meta-analysis of 12 trials and 13 observational studies found that acne patients had significantly lower serum zinc levels, and those treated with zinc (oral or topical) showed meaningful improvement in inflammatory lesions 7.

In practice: Zinc isn’t going to replace established acne treatments like retinoids or benzoyl peroxide, but it may help as an adjunct therapy, particularly for people with confirmed low zinc levels.

6. Depression (as Adjunct Therapy)

Several studies have examined zinc as an add-on to antidepressant medication. A meta-analysis of five trials found that zinc supplementation (7-25 mg daily for 10-12 weeks) significantly reduced depression scores in patients with major depressive disorder who were already taking antidepressants 8.

My assessment: This doesn’t mean zinc treats depression on its own. The evidence specifically supports its use alongside conventional treatment, not as a replacement. The mechanism likely involves zinc’s effects on NMDA receptors and neurotransmitter signalling.

7. Wound Healing

Zinc is essential for cell division and protein synthesis, both of which are needed for wound repair. People with zinc deficiency often experience delayed healing.

The NHS recommends adequate zinc intake for wound healing, particularly in older adults and those with chronic wounds 9. However, supplementing above recommended levels doesn’t accelerate healing in people who aren’t deficient.

8. Blood Pressure

A meta-analysis of 9 trials found that zinc supplementation significantly reduced systolic blood pressure, though not diastolic 10. The mechanism may involve nitric oxide synthesis and antioxidant effects.

Worth considering: The blood pressure reductions were modest. Zinc isn’t a substitute for blood pressure medications, but adequate intake may contribute to overall cardiovascular health.

9. Childhood Pneumonia

Zinc supplementation has been studied as an adjunct treatment for severe pneumonia in children in developing countries where zinc deficiency is common. A meta-analysis found that zinc reduced mortality from severe pneumonia, though it didn’t significantly affect treatment failure rates 11.

10. Gastrointestinal Cancer Risk

A large meta-analysis of nearly 400,000 participants found that those with the highest zinc intake had an 18% lower risk of gastrointestinal cancers, particularly colorectal cancer, compared to those with the lowest intake 12.

Important caveat: This was an observational finding showing correlation, not causation. People with higher zinc intake might have other dietary or lifestyle factors that reduce cancer risk.

11. ADHD in Children

A systematic review found that zinc supplementation improved overall ADHD scores in children, particularly when combined with methylphenidate (Ritalin). However, zinc alone didn’t significantly affect hyperactivity or inattention subscores 13.

12. Anti-Inflammatory Effects

Beyond immune function, zinc has broader anti-inflammatory properties. A meta-analysis found significant reductions in CRP, TNF-α, and malondialdehyde (an oxidative stress marker) with zinc supplementation 14.

13. Blood Lipid Regulation

A large meta-analysis found that zinc supplementation reduced total cholesterol, LDL cholesterol, and triglycerides, with the most significant effects in people with metabolic conditions such as obesity or type 2 diabetes 15.

Where the Evidence Is Weak or Negative

Not all claims about zinc hold up. Here are some areas where the research is disappointing:

Tinnitus: A Cochrane review found no significant benefit from oral zinc for tinnitus symptoms 16.

Measles: Despite theoretical benefits, a Cochrane review found insufficient evidence that zinc helps with measles recovery 17.

Prostate cancer prevention: Despite zinc’s concentration in the prostate, a meta-analysis of nearly 12,000 prostate cancer cases found no clear association between dietary zinc intake and cancer risk 18. In fact, high-dose zinc supplements (over 100 mg daily) have been associated with increased prostate cancer risk 19.

Weight loss: While obese individuals often have lower zinc levels, supplementation doesn’t appear to cause weight loss in most people 20.

Side Effects of Zinc

At recommended doses (up to 40 mg daily for adults), zinc is generally well tolerated. Possible side effects include:

Nausea and stomach upset
Metallic taste in the mouth
Loss of appetite
Headache
Diarrhoea

These typically resolve when you stop taking the supplement or reduce the dose.

Long-term high-dose risks: Taking more than 50 mg daily over several weeks can cause copper deficiency because zinc interferes with copper absorption. Symptoms include anaemia, low white blood cell counts, and neurological problems. For this reason, many zinc supplements include a small amount of copper (typically 2 mg) to offset this effect.

Taking over 100 mg daily long-term may actually suppress immune function rather than enhance it, and has been linked to increased prostate cancer risk.

Safety Precautions and Contraindications

1. Pregnancy and breastfeeding: Don’t exceed the tolerable upper limit (40 mg daily) unless specifically advised by a healthcare provider.

2. Antibiotic interactions: Zinc can reduce the absorption of tetracycline and quinolone antibiotics (ciprofloxacin, norfloxacin, levofloxacin). Take zinc at least 2 hours before or 4-6 hours after these medications.

3. Diuretics: Amiloride (a potassium-sparing diuretic) can increase zinc levels in the blood. Avoid combining with zinc supplements.

4. ACE inhibitors: Blood pressure medications like captopril, enalapril, and lisinopril may reduce zinc levels.

5. Chemotherapy: Don’t take zinc with cisplatin without consulting your oncologist, as it may affect drug efficacy.

6. Immunosuppressants: Since zinc enhances immune function, it may theoretically interfere with immunosuppressive medications like ciclosporin or prednisone.

7. Penicillamine: This medication (used for Wilson’s disease and rheumatoid arthritis) can be less effective when taken with zinc.

8. Other minerals: Zinc competes for absorption with calcium, magnesium, and iron. If taking multiple mineral supplements, space them out or keep total intake under 800 mg to avoid reduced absorption.

Food Sources of Zinc

The best dietary sources of zinc are animal proteins:

Oysters – the richest source by far (74 mg per 85g serving)
Beef – about 7 mg per 100g serving
Crab and lobster – 6-7 mg per 100g
Pork – about 3 mg per 100g
Chicken – about 2.5 mg per 100g
Eggs – about 1 mg per large egg

Plant sources include pumpkin seeds, chickpeas, cashews, and fortified cereals, though the zinc from these foods is less readily absorbed due to phytates that inhibit uptake. Vegetarians may need up to 50% more zinc than meat-eaters to compensate 2.

Recommended Daily Intake

According to UK guidelines, the recommended daily intake is:

Adult men: 9.5 mg
Adult women: 7 mg
Pregnancy: 7 mg (same as non-pregnant women)
Breastfeeding: 9.5-13 mg depending on stage

The US recommendations are slightly higher (11 mg for men, 8 mg for women). The tolerable upper intake level for adults is 40 mg daily from all sources combined.

Final Thoughts

Zinc is genuinely important for immune function, wound healing, and numerous metabolic processes. For people who are deficient, supplementation can make a real difference. For the common cold specifically, zinc lozenges taken early appear to speed recovery.

But zinc isn’t a cure-all. Many of the bold claims you’ll see in marketing materials simply aren’t supported by strong evidence. Taking mega-doses won’t boost your health and may actually cause harm.

If you eat a balanced diet that includes animal proteins, you probably don’t need a zinc supplement. If you’re vegetarian, have a digestive condition, or fall into another at-risk group, it’s worth checking your zinc status and considering supplementation if needed. As with most nutrients, the goal is adequacy rather than excess.

References

Chasapis CT, et al. Zinc and human health: an update. Arch Toxicol. 2012;86(4):521-534.
Wessells KR, Brown KH. Estimating the global prevalence of zinc deficiency. PLoS One. 2012;7(11):e50568.
Hosseini R, et al. Effects of zinc supplementation on inflammatory markers. Biol Trace Elem Res. 2021;199:3995-4015.
Hemilä H. Zinc lozenges and the common cold. JRSM Open. 2017;8(5):2054270417694291.
Wang X, et al. Zinc supplementation improves glycemic control. J Clin Endocrinol Metab. 2019;104(4):1143-1153.
Zhao J, et al. Zinc levels in seminal plasma and male infertility. Sci Rep. 2016;6:22386.
Yee BE, et al. Serum zinc levels and efficacy of zinc treatment in acne. J Drugs Dermatol. 2020;19(1):36-41.
da Silva LE, et al. Zinc supplementation and depression. Nutr Neurosci. 2021;24(12):934-944.
NHS. Vitamins and minerals - Others. www.nhs.uk
Mousavi SM, et al. Zinc supplementation and blood pressure. Hypertens Res. 2020;43(5):419-427.