Some 20-30% of the population in developed countries take a daily vitamin supplement. Does it do them any good? Our current estimates of vitamin requirements are based on the amounts needed to prevent deficiency diseases; in most countries deficiency is no longer a major problem. The question is whether higher levels of intake provide health benefits. There are two ways to answer this question: to identify biomarkers of optimum nutritional status, rather than the absence of deficiency; or epidemiological studies to identify nutrients associated with a lower incidence of chronic diseases, followed by intervention studies. Neither approach has yet provided satisfactory answers, and a recent review finds little convincing evidence in favour of supplements.1

A number of promising suggestions for biomarkers exist, including metabolic markers of damage from radicals, immune responses, and damage to DNA. None is responsive to only a single nutrient, and all are affected by a plethora of non-nutritional factors. 2 3 To …