Q: I teach in a preschool, and I seem to get a cold every two months. I try to wash my hands frequently, but sometimes I still get one. My friends keep telling me...

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Q: I teach in a preschool, and I seem to get a cold every two months. I try to wash my hands frequently, but sometimes I still get one. My friends keep telling me about natural supplements that are supposed to help speed recovery, like Echinacea, but is there anything that has been proven to work?

A: Echinacea is a plant with anti-inflammatory and immune stimulating properties. Some studies suggest that it may reduce cold symptoms by 20 percent, and others don’t. This may partly be due to the fact that the researchers used different Echinacea species and ways of preparing the herb. Echinacea purpurea is currently the species with the most studies to support it. Don’t use it if you have ragweed allergies, because Echinacea is in the same plant family.

Andrographis is a plant from India. Several studies suggest it may be helpful when taken within three days of getting a cold. It can take up to five days to see results. Most research used the product Kan Jang, which is standardized to 4 to 5.6 mg of andrographolide. It can cause nausea and diarrhea in some people.

Zinc is a controversial supplement for colds. Some studies suggest that taking a zinc lozenge every two hours while awake within one to two days of getting a cold may be helpful; others don’t. If you are taking more than 40 mg of zinc for a long period of time, you should talk to your doctor because high doses of zinc can deplete copper levels in the body. I don’t usually recommend zinc nasal sprays because they can cause permanent loss of smell.

Most research suggests that about 1 gram of vitamin C taken at the onset of cold symptoms may shorten the duration of a cold by about a day. Keep in mind that vitamin C can cause diarrhea in high doses.

Although there are no studies using it for colds, one study on Sambucol, a standardized elderberry extract, showed that it shortened the duration of flu symptoms by about 56 percent. It also improved symptoms of fever and muscle pain.

Dr. Astrid Pujari is a Seattle M.D. with an additional degree as a medical herbalist; she practices at the Pujari Center and teaches as part of the residency programs at Virginia Mason and Swedish Providence hospitals. Her column is a weekly feature in Sunday Northwest Life. Send questions to apujari@seattletimes.com for possible use in future columns.