hey say that a little knowledge is a dangerous thing. This adage is never more true when it comes to medical professionals commenting on nutrition. Nutrition and human metabolism are highly complex subjects that require years of study to understand even the basic concepts, and decades more to become fluent in the scientific literature. Nutrition is distinct from pharmacology in that drugs do not work in the same way as nutrients in humans. For example, in pharmacology a drug is bioavailable if it is not metabolised. Metabolism of drugs change their activity and is considered detrimental to their purpose. In nutrition, metabolism of nutrients are very often a pre-requisite to bioavailability, with parent compounds often becoming highly metabolised before exerting their biological effects. Misunderstandings such as this are the reason that doctors and medically trained individuals do not understand nutrition. This coupled to their inadequate nutritional education and training.
Of course for every nutritional misunderstanding conveyed by the medical establishment, there is another that results from deliberate obfuscation. In fact it is becoming common practice for useful idiots to be seen promulgating their falsehoods in the mainstream media to confuse and deter self thought regarding nutrition amongst the general population. The deliberate confusion regarding the benefits of antioxidant nutrients is a great example of such obfuscation that would be worthy of the best propaganda model. Noam Chomsky has written extensively regarding self-censorship in the media, and such similarities between media self-censorship and medical self-censorship help explain some of the apparent ‘confusion’ that results from antioxidant research. In truth, there is no confusion, and although it would be unwise to state that all the answers are apparent, the true student of science should conclude that there is certainly enough evidence to conclude that antioxidant nutrients are at best beneficial and at worst possess no detrimental effects to health.
Antioxidant nutrients are those that possess the ability to inhibit free radical chain reactions through the donation of electrons. This usually occurs through the passing of a hydrogen atom from the antioxidant to the free radical, or pro-oxidant. In the process of donation, the antioxidant, after losing a hydrogen atom, itself because oxidised and can under certain circumstances become a pro-oxidant free radical. If left uncheck this can cause cell and tissue damage and lead to the initiation of the disease process. It was Denham Harman who is credited with first writing about the free radical theory of ageing and disease and his work in the 1950’s and 60’s has been the inspiration for much of the work published to date. From this work it is evident that that antioxidants can become pro-oxidants, and this is not in dispute. However, extrapolation of this concept to conclusions that antioxidants are therefore dangerous and should be avoided as it is unscientific.
Cell culture or in vitro studies are a useful tool to understand physiology and interactions between drugs or nutrients and cells. Much of the understanding of cellular systems has originated from in vitro work and along with animal models is at the core of most cellular understanding. However, in vitro work should always be interpreted with caution because cells in dishes and tubes do not behave in the same way as when in humans. For example, it is easy to show that vitamin C can damage DNA in a test tube. Add supraphysiological levels of vitamin C to cells and the vitamin C will damage the DNA because it will reduce the pH of the media sufficiently to cause DNA damage. This is unrealistic from a human perspective because vitamin C plasma levels are regulated and so in vivo would never reach these high concentrations. Likewise, it is easy to cause cellular damage by adding vitamin E in isolation to cells in culture through addition of a free radical generator. However, vitamin E is never found in isolation in humans.
And here is where an understanding of antioxidant chemistry is required in order to realise that differences exist between antioxidants in tubes and antioxidants in humans. Antioxidants form a complex synergistic recycling pathway in humans that is constructed specifically to prevent antioxidants becoming damaging free radicals. In my article ‘the antioxidant merry-go-round’ (here) I explained that once an antioxidant is converted to its oxidised form through donation of a hydrogen atom, it quickly becomes reduced itself by another antioxidant. For example, vitamin E donates a hydrogen atom and becomes oxidised, but is immediately reduced by vitamin C. In the process vitamin C becomes oxidised to dehydroascorbic acid, but is immediately reduced by cellular by glutathione. Oxidised glutathione is then reduced by NADPH which is produced in the pentose phosphate pathway.
In this way antioxidant nutrients are continually recycled from their reduced to oxidised forms. Dietary plant chemicals can contribute to this system, and are effective because they are always working in synergy with other nutrients. Yes vitamin E can become a pro-oxidant, and yes vitamin C can become oxidised. But they do not cause cellular damage because they are reduced by other nutrients in a continual cycle. Unjustified extrapolation of data from isolated nutrients in a cell culture systems is therefore not relevant unless certain caveats are considered. And while it can be argued that free radical generation is required under certain physiological circumstances such as immune response or cellular apoptosis, these circumstances are closely regulated and there is no evidence that diets high in antioxidants interfere with such systems in any way. In fact evidence shows that antioxidants are beneficial to immunity. For example diets high in the antioxidant nutrient selenium are essential for correct immune function2.
RdB
