They found that those who used supplements tended to be non-smokers who took exercise, weighed less and had slimmer waists and higher blood levels of vitamin B12. Researchers at the Medical Research Council in Cambridge looked at the long-term use of supplements by almost 2,000 people born in 1946. Small sample size and lack of proper controls is another problem. Another challenge for those investigating whether supplements work is that evidence can be influenced by other factors, such as the type of people who participate. Big differences in quality and actual, rather than stated, quantity of products may be one reason for the often conflicting research results. It gives manufacturers seven years to comply with new regulations.

The EU directive on traditional and herbal medicines, which regulates the safety and quality of products, came into force this week. "The same thing is happening here, and I would like to see much greater regulation. "European regulations are coming in which will give greater protection for consumers, but they don't require demonstration of efficacy, either, says Professor Ernst. "Research in America shows that off-the-shelf preparations contain anything between zero and 200 per cent of what it says on the label," says Professor Ernst.

Research at Consumer Lab, an American organisation devoted to testing off-the-shelf supplements, demonstrated that quality varies widely. Out of some 14 ginseng supplements, six did not contain the amounts claimed and three exceeded permitted pesticide levels. While supplements are bought in the belief that they act on the body or mind, there is little or no control over what is in them, or what it does. Those suffering from serious and chronic illnesses, including cancer, diabetes, arthritis, and Alzheimer's are also increasingly turning to supplements. But while there is evidence that some work, the data for most is conflicting or doubtful There is also concern about safety. It's estimated that we now spend more than £300m a year on supplements of one kind or another in the UK, and that demand is increasing, with one in five people using them at some time, and almost half of British women in their fifties regularly popping one or more. Health supplements such as echinacea and black cohosh are big business.