Research led by scientists in the UK has upturned a 50-year old theory that maintains antioxidants stop or slow aging by counteracting the oxidative stress on cells caused by free radicals, a finding that will undermine claims made by beauty and diet products that promote the anti-aging properties of antioxidants.
The research which was funded by the Wellcome Trust, was led by Dr David Gems of the Institute of Healthy Ageing at University College, London, and is published in the 30 November issue of the journal Genes & Development.
Superoxide free radicals are a natural byproduct of metabolism. They are essentially unstable oxygen molecules with too many electrons that go in search of compounds they can bond with that are happy to accept their extra electrons. This process is similar to when iron becomes rusty and turns into iron oxide, except that in the human body, biological mechanisms exist that can stop or reverse it.
In 1956 the biogerontologist Denham Harman proposed that aging was the result of an accumulation of “oxidative stress” such as that inflicted on cells by free radicals. Gems and colleagues now suggest this theory is not correct and that superoxide is not a major cause of aging.
Gems said the free radical theory of aging, which has dominated the field for over 50 years, “just doesn’t stand up to the evidence.”
For this study, he and his team studied the way genes controlled the removal of superoxide from the bodies of Caenorhabditis elegans, a type of nematode worm often used in aging research. They were able to switch the genes on and off and influence the extent to which the worms’ bodies were able to get rid of surplus superoxide and thus reduce the potential damage it could cause through oxidation.
According to the free radical theory, Gems and colleagues expected to see a significant link between the worms’ lifespan and the extent to which their bodies were able to mop up excess superoxide, but this is not what they observed. Another study on mice led by researchers at the University of Texas came to similar conclusions, supporting the idea that the 50-year old free radical theory is not correct, said Gems and his team.
If superoxide is involved in the accumulation of molecular damage that characterizes the aging process, it only plays a small part, said Gems.
“Oxidative damage is clearly not a universal, major driver of the ageing process. Other factors, such as chemical reactions involving sugars in our body, clearly play a role,” he added.
On the strength of these findings, Gems suggested that anti-aging products that claim to have anti-oxidant effects are unlikely to be as effective as they say. He said that while a healthy and balanced diet reduced the risk of developing diseases of aging such as cancer, diabetes and osteoporosis, there was:
“No clear evidence that dietary antioxidants can slow or prevent ageing. There is even less evidence to support the claims of most anti-ageing products,” he said.
Dr Alan Schafer, Head of Molecular and Physiological Sciences at the Wellcome Trust, said this new study should encourage researchers to explore new areas of aging research:
“Research such as this points to how much we have to learn about ageing, and the importance of understanding the mechanisms behind this process,” added Schafer.
“Against the oxidative damage theory of aging: superoxide dismutases protect against oxidative stress but have little or no effect on life span in Caenorhabditis elegans.
Doonan, R. et al.
Genes and Development, Published online 30 Nov 2008.
Sources: UCL, Wellcome Trust.
Written by: Catharine Paddock, PhD