The pursuit of well being coupled with 21st century food phobia has fuelled a booming dietary supplement industry. But just how healthy are all these pills we're popping? Louise Manson investigates

As our awareness of healthy eating has grown, so has our consumption of dietary supplements. We now live in a culture obsessed with health, with 42 per cent of us taking some form of herbal preparation or vitamin, resulting in an industry that is currently worth £400 million a year.

While we are all familiar with the wide range of manufactured vitamins on the market, herbal supplements, which come from plant extracts, have only recently entered the mainstream health industry. We are now constantly bombarded with the merits of Evening Primrose, Ginseng, Echinacea and Gingko biloba to make us fitter, less stressed and ultimately happier and sexier. And with celebrities everywhere claiming they can't live without their daily dose, supplements have become extremely fashionable.

The problem with all these so-called health tonics is that we don't know exactly what is in them or indeed if they are harmful in the long term. It is all too easy to wander into your nearest health food shop for a lemonade 'pick-me-up' and find you are knocking back a drink laced with an untested 'jungle herb'.

The British Dietetic Association, representing the UK's state registered dieticians, argues that supplements should come under tighter regulations and be classed as medicines rather than foods. This would legally oblige a manufacturer to prove that its products were safe, and all products would have to undergo full clinical trials before their launch. Preparations would also have to contain exactly the same dose/ingredient, which at the moment can vary with no upper limit. They are currently unregulated, with no disclaimers and very little information on the labels.

Some nutritionists believe that the supplement industry is preying on our insecurities about health for considerable commercial gain. Catherine Collins, chief dietitian at St George's Hospital in Tooting, London, says, 'certain adverts for dietary supplements very cleverly imply that your diet is likely to be inadequate without them, generating the fear that you can't possibly get what you need from food alone. However, the people who are putting forward the concept of supplements of any kind are those who stand to make money from them.'

Most nutritionists agree that in the vast majority of cases we can get everything we need from a balanced and varied diet made up of low-fat dairy products, lean meat, fish, starchy foods, fruit and vegetables. According to Claire MacEvilly, a nutrition scientist from the British Nutrition Foundation, 'if you're eating a healthy diet, there really is no need to take any dietary supplements, unless you've been advised by your doctor.'

Professor Edzard Ernst, Professor of Complimentary Medicine, University of Exeter, also urges caution when taking herbal supplements. 'The problem with these supplements is that anything that has the potential to do good also has the potential to harm.'

In certain cases, supplements can be invaluable. Current advice from the Department of Health (DoH) is that women planning a pregnancy should take 400mg of folic acid every day, up until the 12th week of pregnancy, to help prevent neural tube defects, or spina bifida, in an unborn baby. To get the equivalent from your diet, you would have to eat six servings of broccoli every day.

The DoH says that dietary supplements should only be taken after medical advice has been sought. This is because of the risk of overdosing on supplements that are widely available, taking the wrong ones or even the wrong combination of them, as the side effects can be devastating.

For example, St. John's Wort can interfere with the effectiveness of anti-depressants and the contraceptive pill; Evening Primrose can provoke epileptic attacks in susceptible patients; and Echinacea may contribute to a range of allergic reactions. Other supplements containing iron, manganese, silver and gold (which can be found in certain Chinese preparations) can lead to chronic renal failure (a malfunctioning of the kidneys.)

It is also not advisable to use herbal remedies if you are undergoing surgery, since they may cause unforeseen complications during the operation. (Ginkgo biloba, which has been linked to excess bleeding, is an example of this.)

Professor Ernst adds 'there is a certain section of the community that are more vulnerable to side effects of herbal and vitamin supplements, such as pregnant women, and there is an awful lot of nonsense being handed out to them by health food shops and herbalists.'

Herbal mixtures can also unwittingly be contaminated with toxic substances, as there are less stringent checks on quality and no regulation on what goes in to them or sell by dates. Often the ingredients can go stale or bad. It is therefore important to always buy reputable brands and beware of 'cowboy companies' who sell through direct marketing.

Companies such as Solgar have been around for a long time and are well established in the supplement industry. Also, certain stores like Boots stock main distributors who are more reliable. If in doubt, check which brands are most reputable with staff in high street health food shops.However, before taking any kind of supplement, it is best to consult your GP, particularly if you suffer from a condition (anything from asthma to IBS) or if you are pregnant. Always read the label carefully and never exceed the recommended dosage.