Due in part to the fact that vitamins are not patentable, and pharmaceutical firms have little to gain by paying the considerable costs of randomized controlled trials (RCTs) for existing natural substances, there is a paucity of RCT data regarding these substances. For example, although folk wisdom holds that vitamin C can prevent the symptoms and lessen the duration of the common cold -- and although two-time Nobel Prize winner Linus Pauling advocated the use of vitamin C to prevent the common cold -- there have been few RCTs to study this assertion. However, a new analysis of existing trial data indicates that vitamin C supplementation can be beneficial for the sufferers of common cold-exacerbated asthma.
Finnish researcher Harri Hemilä has been examining the role of vitamin C -- otherwise known as L-ascorbic acid -- in preventing and treating respiratory ailments, publishing findings over the past few years. A review by Hemilä of existing data indicates that although population-wide data supporting vitamin C supplementation for the reduction of respiratory ailments is scarce, the practice may be warranted among individuals "exposed to brief periods of severe physical exercise." Hemilä adds that "it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them."
Other research published recently in the Journal of Biological Regulators and Homeostatic Agents demonstrates that "Supplementation of vitamin C improves the function of the human immune system, such as antimicrobial and natural killer cell activities, lymphocyte proliferation, chemotaxis, and delayed-type hypersensitivity." The mechanism by which some of these effects are brought about it not completely clear, but the effects themselves are demonstrable.
A team of doctors writing in the journal of the American Academy of Family Physicians in 2012 reports, "Prophylactic vitamin C modestly reduces cold symptoms and duration in adults and children." In particular, the researchers note that children under age 12 may receive a daily dose of vitamin C from 0.2 grams to 2 grams for a period of two weeks to nine months in order to prevent or lessen cold symptoms, and that adults may receive a similar dose (0.25 grams to 2 grams) over a similar period of time (40 days to 28 weeks).
Now, back to Harri Hemilä. The Finnish researcher published a new paper on November 26, 2013, in the journal of Allergy, Asthma, and Clinical Immunology. This time, the analysis focused on trials of vitamin C in individuals suffering from asthma. Hemilä found that all three studies analyzed found benefits of vitamin C supplementation in reducing asthma attacks or against bronchial hypersensitivity, a symptom of asthma. Hemilä asserts that the prophylactic effect of vitamin C against the common cold is at work among these individuals, whose asthma symptoms would be exacerbated by the common cold, and who are thus protected against a worsening of asthma symptoms by the protective effect of vitamin C against the common cold. Again, the recommendation is for individuals to "test vitamin C on an individual basis, if they have exacerbations of asthma caused by respiratory infections."