Zinc and Cold Symptoms

Studies of the effectiveness of zinc supplements in treating the common cold have yielded conflicting results: some have shown that zinc helps, while others find that it has no effect. A recent entry into the fray is a study of 48 cold sufferers at Wayne State University in Detroit. Half of them were given zinc lozenges and half were given placebos -- identical lozenges with no active ingredients. The zinc group's cold symptoms lasted about 4.5 days. Cold symptoms lasted significantly longer in the group taking placebo lozenges: an average of 8 days.

People joined the study within 24 hours of the onset of their cold symptoms, and they were told to take zinc acetate lozenges containing 13 mg of zinc (or placebo lozenges) every 2-3 hours while they were awake. They took no other cold remedies. Each day they recorded (on a scale of zero to 3) the severity of their cold symptoms overall, and of 10 specific cold symptoms: sore throat, nasal discharge, nasal congestion, sneezing, cough, scratchy throat, hoarseness, muscle ache, fever and headache. The symptom scores were totaled each day.

In addition to having shorter colds overall, coughs and nasal discharge were resolved earlier in those patients taking zinc than in the placebo group. Coughing lasted an average of 3.1 days in the zinc group and 6.3 days in patients taking the placebo. Nasal discharge lasted an average of 4.1 days in the zinc group and 5.8 days in the placebo group.

Are there side effects?
Study participants also recorded the presence of various potential side effects to zinc treatment: nausea, abdominal pain, vomiting, diarrhea, constipation, dry mouth, bad taste and mouth irritation. Some people in both groups reported having one or more of these non-cold symptoms, but the zinc group reported significantly more instances of dry mouth and constipation than the placebo group.

Patients in this study took about 80 mg of elemental zinc each day for four or five days. As discussed elsewhere on HealthLink, the recommended daily intake of zinc is15 mg for men and 12 mg for women. The participants in this study were taking five times or more of the recommended amount. The authors of the study caution that this was a high dosage given for a short time only. Indiscriminate use of zinc is not advised, and long term (six to eight weeks) use of high-dose lozenges would likely result in copper deficiency and perhaps other adverse effects. They recommend that if cold symptoms do not show improvement after three days of taking zinc, a patient should be examined to see if they have another type of respiratory tract infection or allergies.

How does it work?
Researches don't know exactly how zinc works to reduce cold symptoms. One hypothesis that this study tested is that zinc reduces the levels of proinflammatory cytokines - substances that are present at increased levels when the body's immune response is activated by an infection. These cytokines may be responsible for producing many of the common cold symptoms. This study did demonstrate that as blood plasma levels of zinc increased, the levels of cytokines declined, but the underlying relationship between zinc and these substances, and their relation to cold symptoms remains to be defined.

The research by Ananda S. Prasad and colleagues is reported in the August 2000 issue of the Annals of Internal Medicine.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.