Madam, - William Reville's article entitled "Why you don't need vitamin supplements" ( Science Today, March 15th) does not accurately reflect what the recent US study on antioxidants shows. Three classic tests for publication bias are: (a) to check if the study summary agrees with the results; (b) to check the basis for inclusion or exclusion of trials; (c) to check and if the studies cited as negative were actually negative. This study fails on all counts.
The conclusion of the study says that "treatment with beta-carotene, vitamin A, and vitamin E may increase mortality", creating the impression that these antioxidants are no good. What it fails to say, yet what is clearly shown in the results, is that "vitamin C given singly, or in combination with other antioxidants did not affect mortality, and selenium given singly or in combination with other antioxidant supplements may reduce mortality".
The summary also fails to say that "beta-carotene or vitamin A did not show an increase in mortality if given in combination with other antioxidants", or that "vitamin E given singly or combined with four other antioxidants did not significantly influence mortality". The obvious take-home message is that antioxidants are team players and that vitamin C and selenium are more beneficial than beta-carotene or vitamin A.
The summary goes on further to degrade antioxidants by deciding which trials (usually the positive ones) are high bias, then excluding them, and which are low bias (usually the negative ones) and only adding these together. For example, it is well known that taking statin drugs, which lower cholesterol and induce CoQ10 deficiency, make vitamin E harmful by turning it into an oxidant. This is an obvious bias but the authors don't even mention this. Once you exclude these trials vitamin E has a positive effect overall.
The final test is to see if the most negative studies were actually negative. One study that skews the results is that of Dr Correa et al from the pathology department at the Louisiana State University Health Sciences Centre in New Orleans. I contacted him and he was "amazed", he said, because his research, "far from being negative, had shown clear benefit from taking vitamins". Correa told us there was no way the study could show anything about mortality. "Our study was designed for evaluation of the progress of precancerous lesions," he said. "It did not intend, and did not have the power, to study mortality and has no value to examine mortality of cancer." Without this study the main conclusion, that antioxidants may increase gastrointestinal cancer, becomes invalid.
Prof Reville's comments that "pregnant women need to be careful that they are getting enough folic acid and should talk to their GP about this. Otherwise we needn't worry." This particularly worrying. The RDA (recommended daily allowance) for zinc is 15mg, and 20mg is recommended in pregnancy since zinc deficiency is linked to growth defects.
According to the Irish Food Consumption Survey the average Irish woman achieves 8.5mg. Zinc deficiency in pregnancy is exceedingly common, so why not supplement it? The blanket statement that "you don't need supplements" ignores the fact that the average intake of vitamin D is 3.7mcg, compared with the RDA of 10mcg, yet a large body of research concludes that intakes of 25mcg per day can halve the risk of some common cancers. Moreover, proper clinical trials show that large amounts of B3 (niacin) lower cholesterol; chromium reverses diabetes; vitamin C reduces the severity and duration of infections; folic acid improves memory and cuts stroke risk by a quarter; and multivitamins raise children's IQ in eight out of 11 trials.
The amounts of nutrients that produce these effects are above the basic RDA levels and certainly above what you will achieve by eating what most people consider a well balanced diet. Of course, diet is the first place to start, but I for one will keep recommending people to supplement their diet with a combination of antioxidants, including selenium and vitamin C, as well as zinc, vitamin D and B vitamins - all found in a high strength multivitamin - because the majority of the trials, including those reviewed in this meta-analysis show benefit, not harm. - Yours, etc,
PATRICK HOLFORD, Founder, Institute for Optimum Nutrition, London SW15.