7 supplements to prevent or treat a cold: Which works best for you?

You're stuffy and sneezing and generally miserable.

Winter colds can be mild or debilitating, but no matter what you're fighting, you might be lured by the promises of a supplement to prevent an oncoming cold or reduce the symptoms of a full blown one.

ConsumerLab.com, an independent lab that evaluates supplements, recently examined the available scientific evidence on the effect of supplements on colds. While a few showed some effectiveness, others were supported by weak or preliminary evidence, often provided by the company producing the supplement, to support their claims.

"When it comes to treating or preventing colds, I'd put them as one step down from maybe," said Tod Cooperman, CEO of ConsumerLab.com.

These include:

Vitamin D supplements:  While these supplements may reduce the occurrence of colds and upper respiratory infections, their effectiveness may be limited to people who lack sufficient Vitamin D. In such cases, moderate daily doses of about 800 IU per day are more effective than extremely large, periodic doses.

One study cited by Cooperman showed that taking megadoses of Vitamin D could actually increase the chances of getting a cold by 40 percent.

DHA: For pregnant and nursing women, 400 mg of DHA from fish or fish oil supplements has been shown to reduce colds in their infants, but only for babies who already have a low intake of DHA.

Beta glucan:  A kind of soluble fiber drawn from sources such as yeast and grains, beta glucan may improve certain measures of immune system function – although preliminary evidence is mixed on whether this reduces the risk of a cold, says ConsumerLab.com. However, there is some evidence that a branded fermented yeast product containing beta glucan may help to increase certain measures of immune function and reduce the occurrence of colds.

Garlic supplements:  Mixed evidence exists on whether garlic supplements combat colds. A single study found taking a garlic supplement daily through the winter reduced the likelihood of catching a cold by almost two-thirds, and those who had colds recovered about one day faster than those who did not take garlic.

Glutathione: An antioxidant that is produced in the liver that plays an important role in immune function, glutathione is sometimes promoted to boost the immune system or help ward off colds. While one small study found that a dose of 500 mg to 1000 mg per day for six months reduced oxidative stress compared to a placebo, there does not appear to be evidence that it prevents colds of reduces cold symptoms.

Melatonin:  Some people report that melatonin helps boost the immune system and promotes sleep during a cold. While very preliminary evidence suggests melatonin possesses some antiviral properties, there does not appear to be any research on colds in people.

Oscillococcinum: While some people have reported preventing colds with this homeopathic treatment, there is little evidence supporting its efficacy. A few studies have found it useful in treating flu, but evidence for this is also slim. And while many other homeopathic remedies have been proposed for preventing or treating colds, there is little quality evidence to support these remedies.