Efficacy of essential mineral for colds remains unproven; new trial shows cut in infection risk and inflammation levels
by Craig Weatherby
The Internet bubble of the late 1990's coincided with fevered interest in the alleged ability of zinc supplements to reduce the risk and severity of colds.
While cold sufferers took to sucking on zinc-infused lozenges, the country's economic fever collapsed under the weight of unrealistic expectations.
The clinical evidence was mixed when zinc first gained its cold-fighting reputation, but there's pretty clear clinical evidence that the mineral can, with fair consistency, help ameliorate those seasonal viral infections.
Researchers at Case Western University conducted the most recent evidence review, which presented this conclusion: “Clinical trial data support the value of zinc in reducing the duration and severity of symptoms of the common cold when administered within 24 hours of the onset of common cold symptoms” (Hulisz D 2004).
Older people tend to suffer zinc deficiencies, and colds aren't the only respiratory infections to which they're especially vulnerable: a list that includes flu, bronchitis, and pneumonia.
Now, new findings indicate that zinc supplements can reduce infection rates and inflammation substantially in older adults.
What the new study shows
Researchers from Wayne State University and the University of Michigan recruited 50 healthy men and women aged 55 to 87 for a randomized, double-blind, placebo-controlled trial (Prasad AS et al 2007).
At the outset of the study, the 50 participants were compared with a group of younger adults, and as expected, they had significantly lower blood levels of zinc and higher levels of markers for inflammation and oxidative stress.
These disadvantages relative to younger adults may help explain why most older people, like those in the study, appear vulnerable to respiratory and other infections and also why they suffer more severe, inflammation-related symptoms.
(We suspect that further analysis would also have revealed the dietary deficiencies of anti-inflammatory, immune-supporting omega-3s that most Americans of all ages display.)
During the 12-month investigation, half of the subjects took 45 mg of zinc, or three times the 15 mg US RDA. They ingested it in the common zinc gluconate form.
The control group took identical-looking placebo pills.
At the end of the one-year study, members of the zinc-supplemented group had suffered fewer infections and had lower levels of inflammatory chemicals and signs of oxidative stress, compared with the placebo group.
These results could simply mean that older adults need zinc supplements to maintain adequate blood levels and balanced immune systems, as the researchers noted in the preamble to their report: “Zinc deficiency, cell-mediated immune dysfunction, susceptibility to infections, and increased oxidative stress have been observed… [in people over 55]” (Prasad AS et al 2007).
Thus, rather than ascribing drug-like powers to zinc, the outcome of this trial may only highlight a common nutritional deficiency in older adults: one that makes them vulnerable to infections and more prone to artery- and brain-damaging inflammation.
How zinc could fight colds
The so-called “rhinoviruses” that cause human colds do so by attaching to “intracellular adhesion molecule-1” (ICAM-1) receptors on the surfaces of the epithelial cells that form the mucous membranes in our nasal passages.
In this study, supplemental zinc reduced expression of ICAM-1 receptors on mucous membrane cells, thereby reducing the ability of cold-causing viruses – and maybe other viruses as well – to gain a foothold in the body.
- Prasad AS, Beck FW, Bao B, Fitzgerald JT, Snell DC, Steinberg JD, Cardozo LJ. Zinc supplementation decreases incidence of infections in the elderly: effect of zinc on generation of cytokines and oxidative stress. Am J Clin Nutr. 2007 Mar;85(3):837-44.
- Hulisz D. Efficacy of zinc against common cold viruses: an overview. J Am Pharm Assoc (Wash DC). 2004 Sep-Oct;44(5):594-603. Review.
- Prasad AS, Bao B, Beck FW, Kucuk O, Sarkar FH. Antioxidant effect of zinc in humans. Free Radic Biol Med. 2004 Oct 15;37(8):1182-90.
- Novick SG, Godfrey JC, Pollack RL, Wilder HR. Zinc-induced suppression of inflammation in the respiratory tract, caused by infection with human rhinovirus and other irritants. Med Hypotheses. 1997 Oct;49(4):347-57. Review.
- Turner RB, Cetnarowski WE. Effect of treatment with zinc gluconate or zinc acetate on experimental and natural colds. Clin Infect Dis. 2000 Nov;31(5):1202-8. Epub 2000 Nov 6.
- Jackson JL, Lesho E, Peterson C. Zinc and the common cold: a meta-analysis revisited. J Nutr. 2000 May;130(5S Suppl):1512S-5S.