Millions of "worried well" Britons are wasting their money and possibly risking their health by taking vitamin supplements, a leading nutritionist has said.
Popular multivitamin supplements are completely pointless for the majority of people on a healthy diet, Professor Brian Ratcliffe argued.
He added that topping up on vitamins could occasionally prove dangerous.
Safe levels of vitamin A can easily be exceeded, for instance, by taking both multivitamin and fish oil supplements, Prof Ratcliffe said.
Excess vitamin A, which accumulates in the liver, led to headaches and nausea, and over a long period of time increased the risk of osteoporosis.
Large doses of vitamin C - taken in the belief they fight colds - may be harmless but are largely excreted and have unpleasant effects on the stomach, said the professor, an expert advisor to the Food Standards Agency.
Speaking at the British Festival of Science at the University of Surrey in Guildford, he pointed out that ideal vitamin intake levels varied enormously between individuals.
"I couldn't tell you what my personal biological requirement is for any vitamin," he said. "All I can do is use the population-based evidence."
He added that large numbers of "worried well" took vitamin supplements as part of a "belt and braces" approach to health.