Before a pharmaceutical company can market a drug and make medical claims for it, it must obtain a medical licence. This will involve clinical trials that cost millions.

That may seem to make the claims for drugs more reliable than a claim for a nutrient. That is not necessarily true, although I recognise that there are sometimes exaggerated claims being made for nutritional products - especially on the internet!

That is why I have been careful to give a comprehensive list of references at the end of each section. I have also restricted any recommendations to nutrients, or combinations of nutrients, that have been subject to trials that have been conducted on humans and not just animal testing. Also where the numbers in the trial are large enough to produce acceptably reliable results. In some cases the evidence is based on whole population studies.

In addition, we can now measure how well nutritional supplements perform on certain outcomes.

For instance, the US Government's Human Nutrition Research Center on Ageing at Tufts University has developed a test which, for the first time, lets us measure the capacity of foods and supplements to act against free radicals. Free radicals are the highly reactive substances that form in the body and can cause oxidative damage to body cells.

The unit of measurement is an ORAC (standing for Oxygen Radical Absorbance Capacity).

The tests show that a diet of five servings of fruit and vegetables a day provides around 1,400 ORAC units - but only a minority of people achieve even that.

I have had my recommended daily formula tested by the ORAC method and it scored over 4,500 ORAC units.

In contrast, six of the UK's leading A-Z multi-vitamin and mineral supplement brands, were tested at the same time using the ORAC method, and scored 114, 144, 168, 192, 204, 302 ORAC units a day respectively.

Anti-oxidant capacity, however, is only one benefit of a nutritional supplement; the ability to reduce inflammation and to improve immune function are at least as important. But these too can be tested. And I have tried to give evidence for these also in the text.

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