Millions of "worried well" Britons are wasting their money and possibly risking their health by taking vitamin supplements, according to a leading Aberdeen nutritionist.

Popular multivitamin supplements are completely pointless for the majority of people on a healthy diet, Professor Brian Ratcliffe from Robert Gordon University argued.

Speaking at a seminar in Guilford, 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.

"They may not be thinking very much about how much they should be taking or whether they should be taking them at all," he said. "People who take multivitamin supplements are probably just wasting their money and boosting the profits of vitamin companies.”

But there is a chance people could be dabbling in areas where there is a potential for harm. Prof Ratcliffe added: "It's a whole new area. We haven't had a significant proportion of the population taking all these supplements before.

"They should certainly speak to a doctor or dietician or nutritionist. I think they'd be better off investing time in trying to choose healthy items for their diet rather than thinking you can bolt on that safety margin by just taking a supplement."

Vitamin A was an example of one micronutrient that was potentially harmful. “You only need to be taking a small amount more than you should be," he said. "If you take a fish liver oil supplement then it has vitamins as well as the fatty acids that you may be unaware of. The safety limit for vitamin A can be passed if you take a multivitamin supplement plus fish oil."

Some groups of the population did need to take extra vitamins, he pointed out.

They included people over the age of 65 who were not good at manufacturing vitamin D in their skin, or absorbing B vitamins. And under Government guidelines, pregnant women were advised to take folate supplements. Vitamin C was one of the most abused vitamins, said Prof Ratcliffe. People often had the mistaken belief that heavy doses of the vitamin staved off colds.

In fact research evidence suggested that vitamin C might shorten the length of a cold but could not prevent one.