What are antioxidants, and are they good for us? (part 1)

Category: Science blog June 24, 2009 Henry Scowcroft Comments are closed

Tetley are in hot water with the Advertising Standards Authority

This entry is part 1 of 3 in the series Antioxidants

Thanks in part to intensive marketing by the food and supplement industries, there’s a widely held belief that if something contains ‘antioxidants’ it’s automatically good for us.

But the scientific evidence behind this claim is pretty thin on the ground – thin enough to lead the Advertising Standards Authority to ask tea-makers Tetley to withdraw their advert for green tea this month.

As the ASA said in their ruling:

We considered that while [the advert] did not imply the tea had the same or similar health benefits to exercise, it did imply that the tea had some general health benefits beyond hydration, in particular because it contained antioxidants.As we had not seen any evidence to demonstrate that green tea, or the antioxidants in it, had general health benefits we concluded that the ad was misleading.

These sorts of claims pop up all the time in advertising, particularly for foods and drinks, as we’ve blogged about before.

Most of them involve products aimed at improving and prolonging health, or preventing disease. And as long as the balance of evidence suggests that these products cause no harm to healthy people, it’s difficult to see how regulators can prevent these sorts of claims being made.

But nevertheless, we’re concerned about the relentless portrayal of antioxidants as a universal health panacea, in the absence of robust scientific data – partly because there’s emerging evidence, including a paper published in the journal Cancer this month, that the knock-on effect is that some people undergoing cancer treatment may be taking them in high doses without thinking to tell their doctors (we’ll look more at this paper in a follow-up post).

This is worrying, because there have also been suggestions that antioxidants might interfere with treatment, at least in some people.

So we thought it would be worth having a look in detail at what, exactly, ‘antioxidants’ are, what they do, how they work, and where the idea that taking antioxidants is good for you actually comes from.

And in a follow up post, we’ll look at the evidence of whether antioxidants are actually good for us.

What is ‘oxidation’?

Oxidation is the technical name for a chemical process that, in general, we associate with things breaking down. For example, oxidation occurs when iron rusts; when a sliced apple goes brown; when copper tarnishes; and when things burn in air

(In the olden days of chemistry yore, oxidation used to be defined as the addition of oxygen to an atom or molecule – hence the name. Nowadays, it’s defined more technically as the loss of electrons from an atom or molecule).

But oxidation reactions are also an essential part of our internal biology. We break down food in our gut, transport it around our bodies, burn it as fuel, and use this released energy to move our muscles or make hormones or new cells – and all of this involves oxidation.

Indeed, every second of every day, our cells are actively directing thousands of different types of oxidation reactions. Far from being ‘a bad thing’, oxidation is a fundamental process of life.

Radical idea

Many oxidation reactions produce ‘free radicals’ – and if antioxidants are the alleged superheroes of good health, then ‘free radicals’ are usually portrayed as the evil baddies, to be ‘mopped up’ at the earliest opportunity.

To briefly get technical again, free radicals are molecules that have an unpaired electron.

Now, rather like people (and for reasons to do with quantum mechanics) electrons strongly prefer to go around in twos. So as a result of this lonely unpaired electron, free radicals have a tendency to steal back an electron from neighbouring molecules.

These nearby molecules in turn become free radicals and go hunting for an electron to restore their own balance, in a molecular game of hot potato.

But because free radical molecules are unstable, they can literally break apart if they don’t find an electron quickly. So if a free radical happens to steal an electron from a key molecule like our DNA, the results can be disastrous.

As a result, our cells have evolved sophisticated ways to protect DNA and other important molecules from bumping into free radicals.

These defences involve molecules that act as ‘antioxidants’ – substances that are able to effortlessly and harmlessly neutralise free radicals. Examples from our own internal biology include enzymes like superoxide dismutase, and vitamins like vitamin C and vitamin E.

Antioxidants in our foods

So that’s the theory: free radicals resulting from natural oxidation can damage our cells; and cells protect themselves from free radicals by making or absorbing antioxidants.

So, you might think, increasing the levels of antioxidants in our bodies must protect us even more. Sadly, to borrow a catchphrase from Ben Goldacre, it’s a bit more complicated than that.

Many experiments have looked at antioxidants’ effects on our cells – both antioxidants found in our bodies, and other ‘natural’ ones like phytochemicals and flavonoids found in plants.

And it’s generally true that such studies have found that antioxidants can indeed protect cells and the molecules inside them from free radical damage.

But there’s a big problem – cells in the lab don’t always behave like cells in the body, and just looking at them on their own reveals very little about how the body behaves as a whole. To understand the bigger picture, you need to look at whole living organisms.

Again, there’s evidence that antioxidants can affect ageing and health in simple organisms like nematode worms, although even here the picture is rather murky. And yet again, it’s difficult to say that the results of these experiments hold true in humans, who are vastly more complex.

Heroes or villains?

Finally, there’s another problem with the simplistic theory that antioxidants = good, free radicals = bad: our bodies also use free radicals in positive ways. They’re not simply villains – they also play an essential role in regulating key systems like our immune system.

For example, certain white blood cells release free radicals that kill bacteria and other nasties. Other evidence, like this study in yeast, suggests that, paradoxically, low levels of free radicals actually help cells protect themselves. Another study found that vitamin supplements (rich in antioxidants) might lessen the beneficial effects of exercise. And these are just a few examples – it seems that our bodies are adept at keeping just the right balance between the right types of antioxidants and free radicals.

So it’s just as easy to speculate that taking extra antioxidants could have negative effects – such as dampening our ability to fight disease – as well as positive ones. We need to look at carefully designed studies of real people to try to work out whether, when or how a diet high in antioxidants is good or bad for us.

Next, we’ll look at what such studies actually say, and what conclusions we can draw from them.



Greenlee, H., Gammon, M., Abrahamson, P., Gaudet, M., Terry, M., Hershman, D., Desai, M., Teitelbaum, S., Neugut, A., & Jacobson, J. (2009). Prevalence and predictors of antioxidant supplement use during breast cancer treatment Cancer DOI: 10.1002/cncr.24378