Zinc and Immune Aging: Why This Mineral Is Critical After 60
More than 300 enzymes require zinc,1 and of all the body's systems, the immune response is the one zinc deficiency affects most severely.2 This article covers what zinc does for immunity, who is at risk of getting too little, and how much is safe, using the NIH Office of Dietary Supplements figures for intakes and limits.
- Zinc is essential for immune function, and a lack of it affects the immune response more severely than other systems.2
- Most people in the US get enough zinc, but older adults are among the groups at higher risk of marginal intakes (NIH Office of Dietary Supplements). Measuring zinc status is hard: a systematic review analyzed 32 potential biomarkers in the search for a reliable one.4
- In a 12-month trial in healthy older people, 45 mg of zinc a day lowered the incidence of infections compared with placebo.6 That dose is above the 40 mg adult upper limit and was given under study supervision.
- The RDA is 11 mg a day for men and 8 mg for women; the upper limit for adults is 40 mg, and chronic excess can cause copper deficiency (NIH Office of Dietary Supplements).
- Oysters contain more zinc per serving than any other food, and beef supplies about 20% of the zinc Americans get from food (NIH Office of Dietary Supplements). Phytate in cereals and legumes blocks zinc absorption, especially when it is not removed during food preparation.5
Zinc was shown to be essential for humans in 1963. At that time only 3 enzymes were known to need it; by 2013, more than 300 enzymes and more than 1,000 transcription factors were.1
Zinc in Immune Function
Zinc works in the immune system in several ways, including as a signaling molecule inside immune cells, and no single function explains why the immune system depends on it so heavily.2
Zinc and Aging
Zinc deficiency, weaker cell-mediated immunity, susceptibility to infections and increased oxidative stress have all been observed in people over 55.6 Zinc is involved in many homeostatic mechanisms, including immune responses, and metallothioneins, proteins that bind zinc, may play key roles in ageing.3
The clearest trial evidence in older people comes from a 12-month study in which 45 mg of zinc a day lowered the incidence of infections compared with placebo.6 The dose was above the adult upper limit of 40 mg, so it is not a self-treatment guide.
Who Is Most Likely to Run Low
The body holds only about 1.5 g of zinc in women and 2.5 g in men, most of it in skeletal muscle and bone. Several groups are at higher risk of getting too little zinc: people with gastrointestinal disorders or who have had bariatric surgery, people who follow vegetarian or vegan diets, women who are pregnant or breastfeeding, exclusively breastfed infants after 6 months of age, children with sickle cell disease and people with alcohol use disorder. In inflammatory bowel disease, about 15% to 40% of people have zinc deficiency, both during flare-ups and in remission (NIH Office of Dietary Supplements).
Testing and Supplementation
Zinc status is difficult to assess: a systematic review of 46 publications analyzed 32 potential biomarkers in the search for a reliable, sensitive and specific one.4 Ask your clinician which test, if any, fits your situation.
Supplements commonly contain zinc sulfate, zinc acetate or zinc gluconate. Absorption from zinc citrate or gluconate is about 61% in young adults, against 50% from zinc oxide, and taking 25 mg or more of iron at the same time can reduce zinc absorption. Stay at or below the 40 mg upper limit unless a clinician advises otherwise (NIH Office of Dietary Supplements).
Zinc for Colds
Trials of zinc for the common cold have had mixed results. Overall, zinc lozenges or syrups appear to shorten colds but not make the symptoms less severe. In these studies zinc is usually given as a lozenge or syrup that briefly coats the mouth and throat, putting it in contact with the cold virus there (NIH Office of Dietary Supplements).
Zinc and Eye Health
In the AREDS trial, participants who took a daily supplement of 80 mg zinc (as zinc oxide) with vitamin C, vitamin E, beta-carotene and 2 mg copper for five years had a 25% lower risk of advanced age-related macular degeneration than those on placebo. The follow-up AREDS2 trial confirmed the benefit in 4,203 participants and found that a formula with 25 mg zinc, about a third of the original amount, gave the same protection (NIH Office of Dietary Supplements). These trials enrolled people who already had signs of the disease, so the formula is a treatment to discuss with an eye doctor rather than a general prevention supplement.
Medication Interactions
Zinc can bind quinolone antibiotics (such as ciprofloxacin) and tetracycline antibiotics in the gut, reducing the absorption of both; taking the antibiotic at least 2 hours before or 4 to 6 hours after a zinc supplement minimizes the problem. Zinc also reduces the absorption and action of penicillamine, a drug for rheumatoid arthritis and Wilson disease, and thiazide diuretics such as hydrochlorothiazide increase the amount of zinc lost in urine (NIH Office of Dietary Supplements).
Put this research into practice: Supplement Evidence Database
References
- 1Prasad AS. "Discovery of human zinc deficiency: its impact on human health and disease." Adv Nutr. 2013;4(2):176-90. PubMed · DOI
- 2Haase H, Rink L. "Multiple impacts of zinc on immune function." Metallomics. 2014;6(7):1175-80. PubMed · DOI
- 3Mocchegiani E, et al. "Zinc, metallothioneins, immune responses, survival and ageing." Biogerontology. 2000;1(2):133-43. PubMed · DOI
- 4Lowe NM, et al. "Methods of assessment of zinc status in humans: a systematic review." Am J Clin Nutr. 2009;89(6):2040S-2051S. PubMed · DOI
- 5Sandstead HH, Freeland-Graves JH. "Dietary phytate, zinc and hidden zinc deficiency." J Trace Elem Med Biol. 2014;28(4):414-7. PubMed · DOI
- 6Prasad AS, et al. "Zinc supplementation decreases incidence of infections in the elderly: effect of zinc on generation of cytokines and oxidative stress." Am J Clin Nutr. 2007;85(3):837-44. PubMed · DOI
