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I recently read an article on Yahoo (but have seen them other places) that claim antioxidants are very important and have health benefits. One article even talked about antioxidants ability to prevent strokes (which I find hard to believe). I've even heard about the mixing of certain antioxidants providing greater benefits.

Is there any real scientific research that support these claims?

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This is a very interesting question, that has been extensively studied and has received great attention. As such, it has often been vandalized by generic press, leaving people quite confused on the matter.

That antioxidants have physiological effects I would say needs no proof: our body utilises antioxidants such as ascorbate (vitamin C) to keep down the amount of free radicals, as can be confirmed by any basic physiology textbook (I can provide references if you need).

To get to the actual point of your question: do antioxidants have the "ability to prevent strokes"? I don't know if the article you read specifically used those words, but this is the type of bad "generic press talk" I was referring to... Antioxidants do not prevent stroke. You can live a super-healthy life, take tons of antioxidants, exercise every day and still have a stroke.

What certain antioxidants can do is to reduce the possibility of having a stroke, which is a very different thing. This is mostly due to the fact that oxidative stress is a risk factor for different cardiovascular diseases.

In the same line of thought, certain antioxidants, in certain regimes and certain situations can help fighting cancer. They DO NOT CURE cancer by themselves, I cannot stress this enough. Again, the idea is that free radicals can damage DNA increasing the risk of cancer. Free radical do not provoke cancer, but they can be a risk factor.

Same for neurodegenerative diseases and many other illnesses where antioxidants can help in certain cases.

It is difficult to generalize because stroke, cancer, neurodegenerative diseases are very broad category of illnesses, that can have the most disparate etiologies. So free radicals are not always the issue and antioxidants are not always the solution. Also, free radicals are actively used by our bodies (e.g. during immune responses) so excess antioxidants is not necessarily good.

The scientific literature at this regard is simply huge and it would be difficult to have a complete bibliography here. Here's a sample of papers and reviews at this regard, if someone who is more in the field knows better papers/reviews please feel free to update my answer (sorry most of these are limited access papers).

Air pollution: mechanisms of neuroinflammation and CNS disease. - Block and Calderón-Garcidueñas, Trends Neurosci., 2009

Oxidative stress and endothelial dysfunction in cerebrovascular disease. - Chrissobolis et al, Front Biosci., 2011

Oxidative DNA damage in mild cognitive impairment and late-stage Alzheimer's disease. - Lovell and Markesbery, Nucleic Acids Res., 2007

Mitogenic signaling mediated by oxidants in Ras-transformed fibroblasts. - Irani et al, Science 1997

c-Myc can induce DNA damage, increase reactive oxygen species, and mitigate p53 function: a mechanism for oncogene-induced genetic instability. - Vafa et al, Mol Cell 2002

and there is many many more.

Not all antioxidants are good, however. For instance, this paper talks about the role of the transcription factor Nrf2, a factor which is involved in the physiological control of free radicals (so we can, by extension, call it an antioxidant inducing factor). The authors show that excess activation of Nrf2 does actually induce tumorigenesis rather then prevent it.

Oncogene-induced Nrf2 transcription promotes ROS detoxification and tumorigenesis. - DeNicola et al., Nature 2011

  • This doesn't really answer the question. It mainly provides the sort of rationale for why it is an interesting question, but that isn't enough to be useful. Only real observations count. – matt_black Feb 7 '13 at 22:42
  • @matt_black: I provided plenty of links to peer-reviewed original papers (=real observations) on the link between antioxidants and cardiovascular diseases. The question is quite generic, so it is really not possible to be more precise than this. – nico Feb 8 '13 at 13:33
  • What I meant was that most of your links are about oxidative stress not about testing sntioxidants. The observational test should be whether, in a controlled trial, antioxidants actually reduce mortality. – matt_black Feb 8 '13 at 13:41
  • @matt_black: OK I see your point, I'll see if I can add some more refs – nico Feb 8 '13 at 14:51
  • Can you quote from the papers and number your links. Anti oxidants like beta carotene can be very bad for smokers for instance. The question does suffer from some issues too. – Tjaart Feb 9 '13 at 14:11
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Antioxidants is a fairly broad class of substances. Depending on what type of stroke and what type of Antioxidant you will get different answers:

In terms of absolute risk, this translates into one additional haemorrhagic stroke for every 1250 individuals taking vitamin E, in contrast to one ischaemic stroke prevented per 476 individuals taking vitamin E.

On the matter of finding it hard to believe that a random substance has a physiological effect: Adjust your priors. A lot of substances that physiological effects that change how the body reacts to various illnesses.

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    can you provide any credible proof to back this answer? – Tony Abrams Mar 8 '11 at 19:43
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Antioxidant supplements have either no measurable effect or actually increase mortality

Vitamin C and selenium seem harmless but don't reduce mortality; Vitamins A, E and beta-carotene increase mortality

There have been many studies of the effects of antioxidant supplements on health. Some of these studies use fairly dubious techniques and study designs but others are better. The best summary of the collective literature is the Cochrane review published in 2012.

We have found no convincing evidence that antioxidant supplements decrease mortality. Even more, beta‐carotene and perhaps, vitamin E and vitamin A seem to increase mortality. Therefore, we cannot recommend the use of antioxidant supplements as a primary and secondary preventive measure in the population groups studied in the present review.

The result comes from about 75 trials with good designs that reported all cause mortality selected from nearly 600 with bias, poor design or inadequate reporting of the mortality. The studies covered:

We considered for inclusion trials that compared antioxidant supplements (that is, beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) at any dose, duration of treatment, and route of administration versus placebo or no intervention.

The results:

Our systematic review contains a number of findings. Beta-carotene, vitamin A, and vitamin E given singly or combined with other antioxidant supplements significantly increased mortality. There is no evidence that vitamin C or selenium may increase longevity. We confirmed that trials with inadequate bias control significantly overestimate intervention effects. The detrimental effect of antioxidant supplements became significantly more pronounced when we excluded all trials with potential confounding. Our findings support and extend our previous findings...

So the trials done well suggest either no obvious effect for some supplements or a small bad effect for others. And as more evidence arrives the results become clearer.

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