You feel a cold coming on, or maybe it's already upon you: the telltale cough, sore throat and stuffy head. You swing by the drugstore, where a shelf full of over-the-counter products containing the mineral zinc claim to be able to shorten the duration of your symptoms.

The promise of relief is tempting. But is it one these products can make good on?

A new analysis of studies published on zinc and cold viruses concludes that there isn't enough evidence to say whether over-the-counter zinc treatments have any effect on preventing the common cold.

For those who pop lozenges or inhale nasal sprays once a cold has come on, the available research together indicates that the products may reduce the duration of symptoms by up to two days, said Daryl Nault, an assistant professor at Maryland University of Integrative Health and first author of the paper, published Wednesday by the nonprofit organization Cochrane.

But those studies are so inconsistent in terms of the dosage, type of zinc, patient population and definition of cold symptoms that "confidence in the evidence is mostly low to very low," the review states. "It is likely that additional studies are required before any firm conclusions can be drawn."

In other words: Nearly 30 years after zinc lozenges first hit the market, we still can't say for sure if these things do what they say they do.

"We aren't saying [zinc] does" have any effect on the common cold, Nault said. "We aren't saying it doesn't. We're saying we need more consistent evidence that is replicable. That's a cornerstone of good science."

The age of zinc cold products dawned in 1996, when researchers from the Cleveland Clinic Foundation convinced 100 clinic employees to volunteer as research subjects within 24 hours of developing a cold.

Half were given placebos, and half were given lozenges containing 13.3 milligrams of zinc from zinc gluconate every two waking hours as long as their symptoms persisted. Those receiving the zinc got better after 4.4 days on average, while the placebo group felt sick for an average of 7.6 days.

Most people consume a sufficient amount of zinc, a vital nutrient, through a regular diet. The mineral is plentiful in red meat and poultry, and present in many grains and fruits. (Oysters contain more zinc per serving than any other known food, with a single serving containing nearly 300% of the daily recommended intake.)

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