Unless you have particular dietary needs, vitamin supplements are probably a waste of money and may even be harmful, a nutritionist told a meeting at the British Science Festival

Some of us wouldn't dream of starting the day without imbibing a carefully considered combination of vitamins, minerals and biochemical supplements. These are taken safe in the knowledge (or delusion?) that we will benefit from good health, longer life and a general feeling of wellbeing.

Speaking yesterday at the British Science Festival, Professor Brian Ratcliffe of Robert Gordon University in Aberdeen argued that most people should simply consume a varied diet containing a number of different vitamins and minerals.

The large number of "worried well" in the UK who take supplements with a "better safe than sorry" attitude are wasting their money while feeding the multi-billion-pound vitamin industry.

Take vitamin C. Despite very little clinical evidence supporting beneficial effects of consuming ultra-high doses of vitamin C, these supplements have become popular for "warding off colds" and other infections. Supplements that contain 1.5g of vitamin C (the equivalent of more than 20 oranges) per dose are widely available. But around 75% of the vitamin ends up down the toilet, said Professor Ratcliffe. Our kidneys simply remove it from the bloodstream.

If you are under 65 and worried about your nutrition he suggests you would be better off visiting a dietician before buying expensive multi-vitamin complexes. There is also a wealth of information available online.

Vitamin supplements do have a role to play for certain groups, he said. For example folic acid is recommended during pregnancy, and over-65s are at risk from vitamin D deficiencies.

On the flipside, some groups are at risk from higher dosages of particular vitamins. Recent research suggests vitamin E supplements can be harmful to smokers.

Presenting his work in collaboration with the Nutrition Society, Professor Ratcliffe argued that research has clearly established at what level we become deficient in a particular vitamin – and the level (if any) at which a vitamin becomes toxic – but has failed to establish with confidence how much of a certain vitamin we should take for "optimum" health effects.

He said the health benefits of a particular vitamin tend to increase as intake rises above an established minimum until an optimum is reached, past which there is no extra benefit and in some cases there is harm. The optimum level varies according to sex, age and many other factors, making it impossible to give an ideal dose that would be suitable for everyone.

• This article was amended on 17 September 2009. We said recent research suggests vitamin A supplements can be harmful to smokers: in fact the research we meant is about vitamin E. This has been corrected.