Vitamin merchants are very active online. They like to cite studies to tell you that vitamin X has been «proven» to be effective against disease Y or to prevent disease Z. But often these studies are of low quality and should not be trusted, as is revealed in this review for the case of arthritis: The effects of the antioxidant vitamins A, C, E, and selenium on several forms of arthritis have been tested in twenty clinical studies, but none of them showed a clear and positive result. Most of these studies are «weak», of «poor quality», and their results are «doubtful», the review authors conclude.
Search vitamin and arthritis with Google. When I did it today, I got more than a million hits. In four of the top ten, beneficial effects of vitamin A, C, E, or selenium are reported, and the first vitamin merchant shows up at position three.
If one study reports an effect and another study denies it, the best we can do is to compare the quality of both studies: Number of cases, time span of the survey, selection criteria for the patients, control for confounding effects, statistical methods and the like. The quality standards of medical studies are generally accepted, and the study cited above has been published at Oxford University Press. This alone does not make it true, but at least trustworthy. Conflict of interest can also be ruled out because the study authors collaborate with a department of complementary medicine.
Get the best for your money
Instead of spending a lot of money on vitamin pills you may fare better with fruit, vegetables and other natural sources of vitamins and minerals. High quality food also has its price, but did you ever enjoy the swallowing of a vitamin pill? Plus it is very likely that nutrients from natural sources are better than from supplements, see my post on calcium.
A last word: If you have a vitamin deficiency or a higher vitamin need and you take vitamin pills by prescription, continue to take them.
(Picture by worldmegan @ Flickr)