British doctor Xand van Tulleken reportedly spent three years examining the effects of popular supplements. He concluded that many do not deliver on their promises and questioned even the benefits of vitamin D, while warning that some substances can have harmful side effects.

Van Tulleken said he had found only a short list of cases in which supplements worked. Collagen for younger skin, vitamin D for stronger bones and turmeric for inflammation were cited in the account, but it did not specify which three cases were considered effective.