Zinc: Immune system and hormone metabolism in check

Zinc is often marketed as a cold remedy. But what's really behind it? Zinc is indeed essential for many bodily functions — but the benefit of a supplement depends largely on how well supplied you already are.

What zinc does in the body

Zinc is an essential trace element involved in over 300 enzymes. It plays a role in cell division, DNA repair, wound healing, the senses of taste and smell, and the production of sex hormones such as testosterone. Without sufficient zinc, the immune system and thyroid do not function optimally.

The body cannot store zinc — unlike iron or vitamin D. This means a regular intake through diet is necessary. According to the reference values of the German Nutrition Society (DGE), the daily requirement is 11 mg for men and 7 to 10 mg for women, depending on phytate intake (phytate binds zinc in the gut and inhibits absorption).

When deficiency is a risk — and who is particularly vulnerable

Zinc deficiency is rare in industrialised countries for people who eat plenty of red meat, seafood and poultry. Oysters have by far the highest zinc content of any food: 100 g provides over 20 mg. Beef, pumpkin seeds, legumes, cheese and whole grains are other relevant sources.

At-risk groups include people who eat primarily plant-based diets (phytate inhibits absorption of plant-based zinc), older adults (reduced absorption capacity), people with chronic inflammatory bowel disease, and those with high alcohol consumption (increased excretion). For these groups, a supplement may be worthwhile — but only after a proper assessment.

What studies show about zinc and the common cold

Zinc lozenges or nasal sprays taken shortly after the onset of a cold can shorten its duration by about one day, according to a Cochrane meta-analysis (2013). The effect occurs mainly when zinc is taken within the first 24 hours of symptom onset. The evidence for preventive use — i.e. ongoing supplementation to prevent infection — is weaker.

The mechanism: zinc ions inhibit the attachment of rhinoviruses (a common cold pathogen) to the mucous membrane cells. This only works with direct contact — which is why lozenges and nasal sprays work better than capsules that are digested in the stomach.

Zinc and testosterone — what's actually to it

Zinc is involved in the synthesis of testosterone, and a pronounced zinc deficiency does indeed lower testosterone levels. Studies show that supplementation in zinc-deficient men normalises testosterone levels. The reverse conclusion — that higher zinc intake beyond what is needed raises testosterone — is not supported by evidence.

Advertising for zinc as a testosterone booster is overstated. In men who are adequately supplied without deficiency, a supplement does not produce measurable hormonal changes. Anyone who wants to check their testosterone levels should do so via a blood test — and only supplement if a concrete deficiency is found.

Dosage and forms

Zinc gluconate, citrate and bisglycinate are well absorbed. Zinc oxide is less bioavailable but found in many budget products. Those supplementing should not keep the daily dose above 25 mg long-term: too much zinc inhibits copper absorption, which can secondarily cause anaemia and neurological problems. The tolerable upper intake level according to the European Food Safety Authority (EFSA) is 25 mg per day for adults.

Zinc should not be taken together with calcium supplements, iron or plant-based foods high in phytate, as these inhibit absorption. On an empty stomach, zinc can cause gastric irritation — taking it with a meal is better tolerated.

Measuring and monitoring with YUTHI

If you want to know how well you are supplied with zinc, a serum zinc test is a good starting point. You can log the result in the YUTHI app and track it over time. The app also helps you incorporate zinc-rich foods into your daily routine — whether you eat meat or follow a plant-based diet. Knowing your status helps you make a more informed decision about whether a supplement makes sense.

Sources

• Prasad AS. Zinc in human health: effect of zinc on immune cells. Mol Med. 2008;14(5-6):353–357.
• Science M. et al. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ. 2012;184(10):E551–E561.
• Netter A. et al. Effect of zinc administration on plasma testosterone, dihydrotestosterone, and sperm count. Arch Androl. 1981;7(1):69–73.
• European Food Safety Authority. Scientific Opinion on the Tolerable Upper Intake Level of zinc. EFSA J. 2006;4(11):437.