Zinc is involved in more than 300 enzymatic reactions in the body and is required for the development and function of virtually every immune cell type. T cell development occurs in the thymus, a gland that shrinks progressively with age in a process called thymic involution. Zinc is required for thymulin, the primary thymic hormone, and zinc deficiency accelerates thymic involution and impairs T cell output. This makes zinc status particularly important for immune competence in older adults, who are both more likely to be deficient and more reliant on T cell-mediated immunity.
Who Is Most at Risk of Deficiency
Zinc absorption is inhibited by phytates, compounds found in grains and legumes, making vegetarians and vegans significantly more vulnerable to deficiency despite potentially adequate dietary intake. Inflammatory bowel conditions, particularly Crohn's disease, cause malabsorption of zinc. Excessive alcohol intake increases urinary zinc excretion. Adults over 60 show reduced dietary zinc absorption and intake. Surveys indicate that up to 10 percent of adults in developed countries are zinc deficient, with higher rates in the groups described, and this figure rises with age.
Zinc and the Common Cold
The evidence for zinc in the treatment of the common cold is among the most replicated in nutritional research. A Cochrane review by Singh and Das, updated in 2013, analysed 16 trials and concluded that zinc lozenges or syrup started within 24 hours of symptom onset significantly reduced the duration and severity of the common cold. The mechanism involves zinc ions binding to rhinovirus proteins, preventing viral attachment to nasal mucosa, and reducing local inflammation. The key is rapid initiation and the use of ionic zinc rather than zinc oxide, which lacks this activity.
Longer-Term Immune Support
Beyond acute infection, adequate zinc status is associated with lower rates of pneumonia, influenza complications, and diarrhoeal illness in older adults. A randomised trial in nursing home residents found that zinc supplementation reduced pneumonia incidence by 41 percent. The immune mechanisms include improved natural killer cell activity, enhanced neutrophil function, and maintenance of mucosal barrier integrity. These effects are most pronounced in those restoring adequate zinc from a deficient state rather than supplementing beyond adequacy.
- Good dietary sources of zinc: red meat, oysters, shellfish, pumpkin seeds, hemp seeds, and hard cheese
- Vegetarians should soak and sprout grains and legumes to reduce phytate content and improve zinc absorption
- At the onset of a cold: zinc acetate or zinc gluconate lozenges, 75 to 80mg elemental zinc daily, starting within 24 hours
- For long-term supplementation: 15 to 25mg elemental zinc daily, taken with food
- High-dose zinc supplementation for more than 8 weeks can deplete copper: balance with 1 to 2mg copper if supplementing long-term
Sources
- Singh, M., & Das, R.R. (2011). Zinc for the common cold. Cochrane Database of Systematic Reviews, 2, CD001364.
- Meydani, S.N., et al. (2007). Serum zinc and pneumonia in nursing home elderly. American Journal of Clinical Nutrition, 86(4), 1167-1173.