Many people take a daily multivitamin in the belief that such an intervention will exert a prophylactic effect and help prevent chronic disease, almost as an ‘insurance policy’ in case their habitual diet doesn’t provide a full spectrum of micronutrients. In Britain alone we spend 360 million a year on vitamin and mineral supplementation, and so from a public health perspective one could ask whether such a vast consumption is truly justified? Lets look at some alternative evidence in support of a healthy diet over supplements in the context of health promotion.

If you consider that it is often those who are health conscious and whom try to eat a balanced diet that choose to take supplements, then it becomes conceivable that many people may be receiving a daily intake of nutrients far in excess of the established RNI’s. Could such a subset of the population therefore be inadvertently exposing themselves to a health risk which is ironically greater than the risk offered by a supposed (and often unsubstantiated) nutrient deficiency? To answer this, lets refer to the results of the two largest meta-analytic type studies on anti-oxidant vitamins (1,2). The first of these two studies was a meta-analysis of 68 randomised clinically controlled trials involving 232,606 participants. This study demonstrated that supplements of beta-carotene, vitamin A and vitamin E actually increased all cause mortality by 5%. Two other anti-oxidant nutrients- selenium and vitamin C- had no effect on mortality. In particular, beta-carotene and vitamin A used singularly was associated with a rather disturbing 7 and 16% increase in relative risk of mortality, respectively.
The second more recent meta-analysis was published in 2008, and collated data from 67 studies, involving 230,000 subjects. The research revealed that vitamin A supplements increased risk of an early death by 16%, beta-carotene by 7% and vitamin E by 4%. In other words, such supplements were actually acting to increase mortality risk. The research also highlighted that vitamin C supplements offered neither an increase or decreased risk of mortality. The researchers of the study from Copenhagen University concluded  that there was “ no convincing evidence that the antioxidants included in vitamin supplements helped to prolong life expectancy”. These studies have clearly cast doubt over the safety and prophylactic efficacy of both single and combined anti-oxidant nutrient intervention. Given that 10-20% of the adult population in North America and Europe consume such supplements, the public health consequences of ill-informed and commercially influenced decisions to take such supplements may be substantial.

Of course not all studies show the same clear picture with regard to diet and supplements. One particular study conducted in 2004 investigated the contribution of supplemental vitamin E and C or dietary vitamin E and C to risk of cardiac events (3). Of the 293,172 subjects included in the meta- analysis, those with the highest intake of vitamin E from dietary sources had a 23% (women) and a 9% (men) risk reduction in cardiac events. Conversely, the data pertaining to the study subjects who took a supplemental form of vitamin E showed that they were ineffective at reducing cardiac risk across the range of dosages consumed (from <37 to >249 IU a day). However, when the data was analysed in context of vitamin C the opposite result was found, e.g. that supplemental vitamin C (>700mg per day) reduced risk of cardiac events by 35% while dietary intake had no effect on cardiac risk. Although in this study supplemental vitamin C appeared to be protective, the results of larger trials (1,2) should always take precedent, and such studies highlighted that supplemental vitamin C  was found to be ‘neutral’ in terms of its effect on health.

A further question mark over vitamin supplements arises when you consider the degree of heterogeneity that exists between outcomes of epidemiological studies and clinical trials of vitamin supplements. For example, epidemiological studies investigating dietary vitamin E and carotenoid intake often show an inverse relationship between intakes of these nutrients and risk of coronary heart disease (CAD) (3). Although epidemiological evidence can never prove causality, the inverse association that exists between dietary intake of such vitamins and risk of CAD can be described as statistically significant and also consistent i.e. the same outcome is often repeated between different studies. However, when it comes to the results of clinical trials investigating anti-oxidants supplements then the results are very conflicting. Indeed although there are studies (3,4) which show a protective effect of supplemental vitamin C and E, the balance of evidence from randomised placebo controlled clinical trials remains on a whole equivocal, and certainly not sufficient to inform a clinical basis for supplemental intervention of anti-oxidants.


Conclusion

Antioxidant supplements are widely used by the general population despite limited evidence of any significant health benefit (1,2). On the other hand, studies investigating diets rich in such nutrients often show a strong and consistent inverse correlation between intake and chronic disease (3). Indeed even patients who are prescribed supplements on medical grounds must still balance the potential prophylactic effect of the nutrient with the possible risk it may have on areas of health. For example a recent study demonstrated that postmenopausal women taking calcium supplements to combat osteoporosis were 50% more likely to have an adverse cardiovascular event than the placebo group (5). In summary, given the potential health risk of some supplements, and the conflicting results of RCT’s investigating anti-oxidant supplements, a far safer and effective means of achieving health is via a balanced and varied diet.

1. Bjelakovic et al., (2007) Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention. Journal Of The American Medical Association, 297, p842

2. Bjelakovic et al., (2008) Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane database of systematic reviews, Apr 16, (2)

3. Knekt et al., (2004) Anti-oxidant vitamins and coronary artery disease risk. American Journal Of Clinical Nutrition, 80, p1508

4. Stephens et al., (1996) A Randomised controlled trial of vitamin E in patients with coronary disease: Cambridge Heart Antioxidant Study (CHAOS). Lancet, p347:781-6.

5. Bolland et al., (2008) Vascular events in healthy older women receiving calcium supplementation. British Medical Journal (e-print, pre-publication).