Zinc

What zinc actually does in your body

Zinc is a cofactor in over 300 enzymes. It's involved in DNA repair, protein synthesis, cell division, hormone production, and immune regulation. Your body can't store it, which means you need a steady supply from food or supplements. The recommended daily intake is 11 mg for men and 8 mg for women, though needs increase during pregnancy, breastfeeding, and periods of high physical stress ^[1].

What makes zinc particularly relevant for longevity is its connection to immunosenescence, the gradual decline of immune function with age. A 2023 narrative review found that zinc deficiency accelerates age-related changes in blood cell production and increases susceptibility to infections, autoimmune conditions, and certain cancers ^[2]. Population data from the NIH suggests that 35-45% of adults over 60 have zinc intakes below recommended levels ^[1]. That's a problem, because even marginal deficiency impairs immune surveillance and wound healing without producing obvious symptoms.

Zinc and immune function: what the evidence says

The 2024 Cochrane review on zinc and the common cold analyzed 34 trials with 8,526 participants. The conclusion: zinc can shorten cold duration by roughly two days when taken at symptom onset, but it doesn't do much for prevention ^[3]. That's consistent with what we know about zinc's mechanism. It supports T-cell and B-cell maturation, regulates inflammatory cytokines, and maintains barrier function in the gut and respiratory tract. When you're already fighting an infection, extra zinc gives your immune system more raw material to work with.

A systematic review and meta-analysis of randomized clinical trials found that zinc supplementation decreased C-reactive protein, TNF-alpha, and IL-6 levels while increasing CD3 and CD4 T-cell counts ^[4]. These are markers that matter for long-term health, not just acute infections. Chronic low-grade inflammation (sometimes called inflammaging) is a driver of cardiovascular disease, neurodegeneration, and metabolic dysfunction. Maintaining adequate zinc status is one way to keep that inflammatory baseline in check.

Zinc, testosterone, and hormonal health

A 2022 systematic review confirmed a clear correlation between serum zinc levels and testosterone concentrations ^[5]. In one often-cited clinical trial, older men with marginal zinc deficiency who supplemented for six months nearly doubled their testosterone levels. That said, the effect is strongest in people who are actually deficient. If your zinc levels are already normal, supplementing more won't keep pushing testosterone higher. Zinc also supports thyroid hormone conversion (T4 to T3) and is needed for proper insulin signaling, making it relevant for metabolic health broadly.

Zinc and aging: telomeres, inflammation, and cellular repair

A cross-sectional study of 3,793 US adults found that every 5 mg increase in daily zinc intake was associated with 0.64% longer telomere length in people aged 45 and older ^[6]. Laboratory research has shown that zinc sulfate treatment increases telomerase activity and reduces the percentage of senescent cells in mesenchymal stem cells ^[7]. The mechanism likely involves metallothioneins, zinc-dependent proteins that function as antioxidants and protect DNA from oxidative damage.

Research on zinc and the gut microbiome adds another layer. Both zinc deficiency and excess alter microbial composition, particularly affecting populations of Lactobacillus and Akkermansia species that are associated with gut barrier integrity ^[8]. The relationship between zinc status, gut health, and systemic inflammation is bidirectional: poor zinc status weakens the gut barrier, which increases inflammation, which further depletes zinc.

Choosing a zinc supplement

Not all forms are equal. A 2024 narrative review comparing zinc supplement bioavailability found that zinc bisglycinate was 43% more bioavailable than zinc gluconate ^[9]. Zinc picolinate is the only form that significantly raised zinc levels in hair, urine, and red blood cells compared to placebo in head-to-head trials. Zinc oxide, despite containing the most elemental zinc per capsule, has the poorest absorption.

For general supplementation, zinc bisglycinate or zinc picolinate at 15-30 mg daily is a reasonable range. Take it with food to reduce nausea, and separate it from iron or calcium supplements by at least two hours, since they compete for absorption. If you supplement zinc long-term at doses above 25 mg, add 1-2 mg of copper to prevent zinc-induced copper depletion, a well-documented risk that can impair red and white blood cell function ^[1]. Intranasal zinc products should be avoided entirely due to documented cases of permanent loss of smell.

Who should test their zinc levels

Vegetarians and vegans (plant phytates block zinc absorption), older adults, athletes with heavy sweat losses, people with digestive disorders like Crohn's or celiac disease, and anyone taking proton pump inhibitors long-term. Serum zinc is the most common test, but red blood cell (RBC) zinc gives a more accurate picture of long-term status. If you're in a high-risk group, testing before supplementing lets you dose appropriately rather than guessing.