Vitamin C

Mechanism of action: Vitamin C is required for the immune system to function well. It enhances lymphocyte activity, enhances phagocytosis, increases chemotaxis of neutrophils, and possibly increases antibody and interferon production. Vitamin C is also an antioxidant.

How to use it: Doses of 200 mg or more have been studied for treating the common cold.

Products to use: ConsumerLab.com purchased 29 brands of vitamin C-containing products (27 for adults and 2 for children). All of the 29 products tested met their claims for vitamin C and all applicable pill forms could disintegrate properly for absorption. Examples of tested products include CVS Pharmacy Vitamin C, Nature Made Vitamin C, and Emergen-C.

Results to expect: One trial, using high doses of four grams or eight grams, reduced the duration of cold symptoms, while six other trials had non-significant results. Three trials showed a non-significant trend towards fewer days missed from work or school. There was no evidence to support reduction of symptoms with Vitamin C.

Side effects: Patients have reported GI symptoms, such as nausea, vomiting, heartburn, abdominal pain, and diarrhea. Doses greater than two grams can lead to an osmotic diarrhea.