Summary
Zinc is an essential trace mineral that the body cannot store, making regular dietary intake vital. It is a cofactor in over 300 enzymes and participates in DNA synthesis, protein production, wound healing, reproductive function, and every aspect of immune defence — from skin barrier integrity to T-cell activation.
Zinc deficiency is more common than often recognised, particularly in vegetarians, vegans, older adults, and people with gastrointestinal disorders. The classic features — impaired wound healing, frequent infections, and hair loss — are often attributed to other causes until levels are tested.nnSerum zinc is the most widely available zinc status marker, though it only reflects about 1% of total body zinc and can be affected by recent meals and acute-phase responses. Testing with a morning fasting sample improves accuracy.
What It Is
Zinc is found in virtually every cell in the body. It is a structural component of zinc-finger transcription factors (proteins that regulate gene expression), a catalytic component of enzymes involved in digestion, metabolism, and DNA repair, and a critical signalling molecule in immune cell communication.nnBecause the body has no dedicated storage mechanism for zinc beyond its concentration in muscle and bone, the serum zinc level is sensitive to fluctuations in dietary intake. Red meat, shellfish (particularly oysters), legumes, nuts, and seeds are the richest sources. Phytates in wholegrains and legumes can inhibit absorption, making zinc more available from animal sources.nnZinc also has a critical role in thyroid hormone metabolism — deficiency can impair T4-to-T3 conversion alongside selenium deficiency.
Functions
Immune function
Essential for the development, activation, and function of T cells, B cells, and natural killer cells. Zinc deficiency causes profound immune suppression.
Wound healing and tissue repair
Required for cell proliferation, collagen synthesis, and inflammatory resolution — the three phases of wound repair all depend on adequate zinc.
Reproductive health
Critical for sperm production, testosterone synthesis, ovarian function, and foetal development — deficiency impairs both male and female fertility.
Taste, smell, and neurological function
Zinc deficiency causes loss of taste (dysgeusia) and smell (anosmia) and impairs neurotransmission, mood, and cognitive performance.
Reference Ranges
Serum Zinc
Measured in µmol/L| Status | Range (µmol/L) | What it means |
|---|---|---|
| Deficient | < 10 | Low zinc — immune impairment, impaired wound healing, and reproductive dysfunction likely. |
| Borderline | 10–12 | Sub-optimal zinc — subtle immune and metabolic effects possible, particularly in high-risk groups. |
| Optimal | 12–18 | Adequate zinc for normal enzymatic, immune, and reproductive function. |
| Elevated | > 18 | High zinc — usually from supplementation. Excessive zinc supplementation impairs copper absorption. |
Serum zinc varies with the time of day, recent food intake, and inflammatory status. Interpret alongside CRP and in the context of symptoms. Plasma zinc is more stable than serum zinc and may be preferred in some laboratories.
Symptoms of Imbalance
Zinc deficiency produces a wide range of symptoms spanning immunity, skin, reproduction, and cognition.
- Frequent infections and slow recovery from illness
- Impaired or slow wound healing
- Hair thinning and loss
- Loss of taste and smell (dysgeusia and anosmia)
- Poor night vision
- Skin conditions — acne, eczema, or dermatitis
- Low mood, irritability, and cognitive difficulties
- Reduced fertility in both men and women
- Nausea and vomiting (acute toxicity from high-dose supplements)
- Abdominal cramps and diarrhoea
- Copper deficiency symptoms (anaemia, neurological effects) from zinc-copper competition
- Metallic taste in the mouth
- Reduced HDL cholesterol with chronic excess
Causes of Imbalance
- Vegetarian and vegan diets (lower zinc bioavailability from plant sources)
- Older age (reduced absorption and dietary intake)
- Coeliac disease and Crohn's disease (malabsorption)
- Alcohol excess (increases zinc excretion and reduces absorption)
- Sickle cell disease and haemolytic anaemia (increased zinc turnover)
- Chronic kidney disease
- Medications (ACE inhibitors, thiazide diuretics)
- Excessive zinc supplementation
- High-dose zinc lozenges taken during illness
- Occupational zinc exposure (galvanising, welding)
FAQs
Zinc is present in many plant foods — legumes, nuts, seeds, wholegrains, and fortified cereals — but its bioavailability is lower than from animal sources. Phytates (found in wholegrains and legumes) bind zinc and reduce absorption. Soaking, sprouting, and fermenting legumes improves bioavailability. Vegetarians and vegans may need 50% more dietary zinc than omnivores and should consider regular testing.
Zinc supplementation can reduce the duration and severity of common colds when taken within 24 hours of symptom onset (zinc lozenges, approximately 80–92 mg/day of elemental zinc). For general immune support, ensuring adequate dietary zinc is the priority. Supplementation should match the degree of deficiency confirmed by testing — excessive supplementation can impair immune function by depleting copper.
Yes. Zinc is critical for testosterone synthesis in men and sperm development — male infertility with low zinc often improves with supplementation. In women, zinc supports ovarian function and egg quality. However, zinc should only be supplemented if deficiency is confirmed, as excess zinc impairs other aspects of reproductive hormone balance.
Yes. High-dose zinc (> 40 mg/day for prolonged periods) competitively inhibits copper absorption, potentially causing copper deficiency — which presents with anaemia and neurological symptoms. If supplementing zinc at doses above 25 mg/day, including a small copper supplement (1–2 mg/day) is generally recommended. Testing both zinc and copper is advisable when using high-dose supplementation.
Zinc bisglycinate and zinc picolinate are generally the most bioavailable forms, followed by zinc acetate and zinc citrate. Zinc oxide (common in cheap multivitamins) has lower bioavailability. For acute supplementation (e.g. colds), zinc acetate lozenges have the most clinical evidence for antiviral efficacy.
References
- Prasad AS. Zinc in human health: effect of zinc on immune cells. Mol Med. 2008;14(5–6):353–357. View source
- King JC. Zinc: an essential but elusive nutrient. Am J Clin Nutr. 2011;94(2):679S–684S. View source
- Hambidge KM, Krebs NF. Zinc deficiency: a special challenge. J Nutr. 2007;137(4):1101–1105. View source