We all agree that if we could return to a comfortable, stress-free, agrarian 19th century life as landowners or farmers, rather than the overworked, underfed farm workers, that our vitamins would be much better taken in the form of freshly grown and picked vegetables. As we can't, we may have to make do with a good multivitamin and mineral supplement.

A far deeper analysis of the present and past health of the people taking part in nearly 50 selected trials together with details of the rest of their diet, their weight and their personality type is needed before conclusions should be drawn from it. We should also know what assessment was made of the strength of the vitamins and the type of vitamins that were being taken, and how strict the people were about doing so. Doctors are aware that few patients score highly on compliance when it comes to taking tablets and I suspect the same thing applies to those who take vitamins at their own volition.

If you don't give yourself a healthy diet and don't prepare the majority of your own meals with non-processed ingredients then the food and nutrition industry will manipulate you to their own ends. If you do eat a healthy balanced diet you won't need any of the rubbish food or the "advice" of "nutrition experts." * Stephen Roberts, Nairobi, Kenya

Yes. I think we would all agree that if we ate food prepared in our own kitchens by a good cook, and the produce had been grown or raised in an attached garden with good soil, we would do better than having to take convenience foods. However not many of us have this privilege. In so far as the metanalysis of studies of vitamin intake is concerned, I would say that when I see patients who appear to be rational, well-orientated and prosperous, even if overworked, it does seem that those who are often taking a multi vitamin do rather better than the vitamin-less people living in flats on inner city housing estates.

All companies will try and market their own products. Society and market forces need to try to persuade them to make certain that the products they are marketing are not only lucrative to the shareholders but nutritious to their customers. When I first had any involvement as a medical advisor to industry the golden rule was that the customer came first, the staff next and the shareholder last. In the last fifty years the order has been reversed. It is now the shareholder and the bonus seeking top executives who come first and it is a bit of a toss-up if it is the customer or the minions in the company who are least important.

Of course the body's best source of nutrition is food. However, modern farming and agricultural practices have failed to produce highly nutritious foodstuffs. Many tests have shown that vitamin and mineral content of today's foods is much less that when compared to fifty years ago. It is important to supplement the diet but remember supplements are just that - a "supplement" to one's diet; they in no means should replace foods. But it's important that supplements are in a form that the body can recognise and therefore utilise. Synthetic supplements are not as effective as whole food supplements. * Nicola, New Zealand

Almost entirely my own point of view but I am not certain that all the faults of the modern diet are the fault of current farming practices, however unattractive some may be. I suspect that the loss of vitamins is more likely to stem from the distances that food is transported and the time it takes before it has reached the supermarket shelves and is available to the public. The mineral content depends very much on where the produce was grown and the state of the soil. For centuries it was known that mineral content varies enormously from one part of a country to another and from one country to another. As world trading has become global we can't be certain that our grain hasn't been grown in a selenium-denuded patch of mid-western America, or our fish caught in a mercury-enriched sea near an industrial centre.

It is much better to have an actual vegetable in which there will be a wide mixture of organic compounds than to have a prepared supplement of one, the most prominent and important compound, in that vegetable. However, as you so rightly say, these pills should be supplements and not replacements and as we are now living in a global economy my opinion is still that supplements are needed. I always quote the example of folic acid, a vitamin that some doctors sixty years ago realised could benefit pregnant women and was later shown to dramatically reduce the rate of abnormal babies born to them. Unfortunately the teaching of such obstretricians as my own boss and mentor, Mr David Stern, about the value of folic acid took about forty years to be accepted during which time hundreds of thousands of children must have been born with potentially fatal neurological defects such as spina bifida, hydrocephalus or anencephalic deformities babies.

There is a big difference between increasing your intake of vitamins and minerals from supplements or by eating more fruit and vegetables. Vitamins and minerals in supplements are in a more concentrated form, may be absorbed more rapidly and might interact with and cancel out the effects of other vitamins and minerals. In contrast, eating more fruit and vegetables increases your intake of all sorts of potentially healthy substances and in a more balanced way. I think it always was a bit naive to think that a daily supplement could offset the effect of not eating enough fruit and vegetables. There really is no alternative. The risks of beta-carotene supplements, especially to smokers, have been known for over ten years but the message has not got through very well. * Anne, Hertford

Yes. There is general agreement that five different types of fruit and vegetable a day, so long as vegetables are reasonably fresh and haven't been flown thousands of miles or driven hundreds, are better than vitamins and minerals in concentrated form. There is also agreement that it is the balance of the many vitamins, polyphenols and minerals within the vegetable as well as their quantities that also matter. Studies have shown, for example, that if a patient takes large quantities of one mineral, however valuable, and even as common as iron, this might inhibit the absorption of another mineral and cause unexpected difficulties. A daily supplement may not entirely offset the effect of not eating enough fruit and vegetables but it may help to, witness the effect of the vitamins that were handed out to children in Britain during the war. Beta carotene supplements in smokers is an especially interesting subject as it was only a minority of smokers with a particular tissue type who suffered more from if they smoked and also took beta carotene supplements.

This is the usual statistical clap-trap you get from the self-styled "experts". I have Type 1 diabetes and I know from my own experience that if I take adequate amounts of vitamins and minerals (notably B group and Magnesium) I feel very much better and have much more energy. Yes, taking too much vitamin A will poison you but ordinary food simply does not contain enough of some vitamins. This is especially true as you get older. In my experience it is wise to supplement. *Adrian Gilbert, Tonbridge, UK

Yes. Most of the letters we have had today would agree with your point of view. Some of us may need supplements to compensate for the deficiencies of the average diet. You also raise the very interesting point of the value of supplements to groups of people whose absorption of vitamins may be poor either because of age or some condition from which they suffer. I don't know for how long you have had type 1 diabetes but absorption can occasionally be a problem in diabetic patients and so it may well be that you have found a way of overcoming this trouble for yourself.