Zinc

Zinc is an essential trace mineral present in approximately 2-3 g in the adult body, second only to iron among trace minerals by abundance. Zinc functions as a structural or catalytic cofactor for over 300 enzymes across all six enzyme classes, and as a structural component of more than 2,000 transcription factors — primarily via zinc-finger domains that mediate DNA and RNA binding. Zinc also serves as a second messenger in certain signaling contexts.

Requirements

The 2001 NAM DRI set RDAs of 11 mg/day for men ages 19+ and 8 mg/day for women 19+, with higher values during pregnancy (11-12 mg) and lactation (12-13 mg). The Tolerable Upper Intake Level is 40 mg/day; sustained intake above this level antagonizes copper absorption, producing secondary copper deficiency with microcytic anemia and neurological manifestations.

Biological functions

Zinc's functions span: (1) enzymatic catalysis — carbonic anhydrase, alcohol dehydrogenase, matrix metalloproteinases, DNA/RNA polymerases, superoxide dismutase 1; (2) transcription factor structure — zinc finger motifs in the glucocorticoid receptor, Sp1, Krüppel family, and p53 tumor suppressor; (3) immune function — T-cell maturation in the thymus, cytokine signaling, neutrophil function; (4) taste and smell — zinc-containing gustin in saliva; (5) wound healing — matrix metalloproteinase activity and collagen synthesis; (6) reproduction — spermatogenesis and testicular function; (7) growth — IGF-1 signaling and cellular proliferation.

Deficiency

Clinical zinc deficiency manifests as: growth retardation in children, delayed sexual maturation, impaired immune function (recurrent infections, reduced T-cell function), delayed wound healing, diarrhea, dermatitis (particularly acral, periorificial, and perineal distribution), alopecia, and hypogeusia (diminished taste). The severe inherited condition acrodermatitis enteropathica, caused by SLC39A4 (ZIP4) mutations, produces classic clinical zinc deficiency reversible with oral zinc supplementation. Marginal zinc deficiency is common in low-income populations with cereal-based diets high in phytate and may affect approximately 15% of the global population per WHO estimates.

Bioavailability

Dietary zinc bioavailability depends on both zinc concentration and meal-composition factors. Zinc absorption is 30-40% from animal products and 10-20% from high-phytate plant foods, reflecting phytate's strong chelation of zinc. The phytate:zinc molar ratio is a useful predictor: ratios above 15:1 indicate substantially impaired absorption; below 5:1 indicates good availability. Fermentation, germination, and soaking of grains and legumes reduce phytate and improve zinc availability.

Dietary sources

Per USDA FoodData Central (mg Zn per 100 g): oysters 74 (extraordinary concentration), beef (chuck roast) 7, lamb 5, crab 7, pumpkin seeds 7.8, cashews 5.8, chickpeas 1.5, lentils 1.3, chicken 1, yogurt 0.6, cheddar cheese 3, fortified breakfast cereals 3-15 depending on brand. Oysters are in a class by themselves; beef and seafood are the next most dense sources.

Supplementation considerations

Common supplemental forms include zinc gluconate, zinc citrate, zinc picolinate, and zinc sulfate, with broadly similar bioavailability. Zinc-for-cold supplementation (lozenges providing ~75 mg elemental zinc per day) showed modest reduction in common cold duration in some trials but a Cochrane review has found the evidence mixed and plagued by bias. Chronic high-dose zinc (>40 mg/day) requires monitoring of copper status. Zinc on an empty stomach can cause nausea; food co-consumption reduces tolerability issues but also reduces absorption.

COVID-era research

Interest in zinc for respiratory viral illness intensified during the COVID-19 pandemic, with multiple hypothesized mechanisms including inhibition of viral RNA polymerase activity. Randomized trials (including COVID A to Z) produced mixed results; zinc is not currently a standard treatment recommendation but remains relevant to maintaining immune-adequate zinc status.