Bad Science

transported, and how the incidental products from that process are used, or bolted onto something else to be transported in the blood, and then ditched at the kidneys, or metabolised down into further constituents, or turned into something useful elsewhere, and so on. This is one of the great miracles of life, and it is endlessly, beautifully, intricately fascinating.

Looking at these enormous, overwhelming interlocking webs, it’s hard not to be struck by the versatility of the human body, and how it can perform acts of near alchemy from so many different starting points. It would be very easy to pick one of the elements of these vast interlocking systems and become fixated on the idea that it is uniquely important. Perhaps it appears a lot on the diagram; or perhaps rarely, and seems to serve a uniquely important function in one key place. It would be easy to assume that if there was more of it around, then that function would be performed with greater efficiency.

But, as with all enormous interlocking systems – like societies, for example, or businesses – an intervention in one place can have quite unexpected consequences: there are feedback mechanisms, compensatory mechanisms. Rates of change in one localised area can be limited by quite unexpected factors that are entirely remote from what you are altering, and excesses of one thing in one place can distort the usual pathways and flows, to give counterintuitive results.

The theory underlying the view that antioxidants are good for you is the ‘free radical theory of ageing’. Free radicals are highly chemically reactive, as are many things in the body. Often this reactivity is put to very good use. For example, if you have an infection, and there are some harmful bacteria in your body, then a phagocytic cell from your immune system might come along, identify the bacteria as unwelcome, build a strong wall around as many of them as it can find, and blast them with destructive free radicals. Free radicals are basically like bleach, and this process is a lot like pouring bleach down the toilet. Once again, the human body is cleverer than anybody you know.

But free radicals in the wrong places can damage the desirable components of cells. They can damage the lining of your arteries, and they can damage DNA; and damaged DNA leads to ageing or cancer, and so on. For this reason, it has been suggested that free radicals are responsible for ageing and various diseases. This is a theory, and it may or may not be correct.

Antioxidants are compounds which can – and do – ‘mop up’ these free radicals, by reacting with them. If you look at the vast, interlocking flow chart diagrams of how all the molecules in your body are metabolised from one form to the next, you can see that this is happening all over the shop.

The theory that antioxidants are protective is separate to – but builds upon – the free radical theory of disease. If free radicals are dangerous, the argument goes, and antioxidants on the big diagrams are involved in neutralising them, then eating more antioxidants should be good for you, and reverse or slow ageing, and prevent disease.

There are a number of problems with this as a theory. Firstly, who says free radicals are always bad? If you’re going to reason just from theory, and from the diagrams, then you can hook all kinds of things together and make it seem as if you’re talking sense. As I said, free radicals are vital for your body to kill off bacteria in phagocytic immune cells: so should you set yourself up in business and market an antioxidant- free diet for people with bacterial infections?

Secondly, just because antioxidants are involved in doing something good, why should eating more of them necessarily make that process more efficient? I know it makes sense superficially, but so do a lot of things, and that’s what’s really interesting about science (and this story in particular): sometimes the results aren’t quite what you might expect. Perhaps an excess of antioxidants is simply excreted, or turned into something else. Perhaps it just sits there doing nothing, because it’s not needed. After all, half a tank of petrol will get you across town just as easily as a full tank. Or perhaps, if you have an unusually enormous amount of antioxidant lying around in your body doing nothing, it doesn’t just do nothing. Perhaps it does something actively harmful. That would be a turn-up for the books, wouldn’t it?

There were a couple of other reasons why the antioxidant theory seemed like a good idea twenty years ago. Firstly, when you take a static picture of society, people who eat lots of fresh fruit and vegetables tend to live longer, and have less cancer and heart disease; and there are lots of antioxidants in fruit and vegetables (although there are lots of other things in them too, and, you might rightly assume, lots of other healthy things about the lives of people who eat lots healthy fresh fruit and vegetables, like their posh jobs, moderate alcohol intake, etc.).

Similarly, when you take a snapshot picture of the people who take antioxidant supplement pills, you will often find that they are healthier, or live longer: but again (although nutritionists are keen to ignore this fact), these are simply surveys of people who have already chosen to take vitamin pills. These are people who are more likely to care about their health, and are different from the everyday population – and perhaps from you – in lots of other ways, far beyond their vitamin pill consumption: they may take more exercise, have more social supports, smoke less, drink less, and so on.

But the early evidence in favour of antioxidants was genuinely promising, and went beyond mere observational data on nutrition and health: there were also some very seductive blood results. In 1981 Richard Peto, one of the most famous epidemiologists in the world, who shares the credit for discovering that smoking causes 95 per cent of lung cancer, published a major paper in Nature. He reviewed a number of studies which apparently showed a positive relationship between having a lot of ?-carotene onboard (this is an antioxidant available in the diet) and a reduced risk of cancer.

This evidence included ‘case-control studies’, where people with various cancers were compared against people without cancer (but matched for age, social class, gender and so on), and it was found that the cancer-free subjects had higher plasma carotene. There were also ‘prospective cohort studies’, in which people were classified by their plasma carotene level at the beginning of the study, before any of them had cancer, and then followed up for many years. These studies showed twice as much lung cancer in the group with the lowest plasma carotene, compared with those with the highest level. It looked as if having more of these antioxidants might be a very good thing.

Similar studies showed that higher plasma levels of antioxidant vitamin E were related to lower levels of heart disease. It was suggested that vitamin E status explained much of the variations in levels of ischaemic heart disease between different countries in Europe, which could not be explained by differences in plasma cholesterol or blood pressure.

But the editor of Nature was cautious. A footnote was put onto the Peto paper which read as follows:

Unwary readers (if such there are) should not take the accompanying article as a sign that the consumption of large quantities of carrots (or other dietary sources of ?-carotene) is necessarily protective against cancer.

It was a very prescient footnote indeed.

The antioxidant dream unravels

Whatever the shrill alternative therapists may say, doctors and academics have an interest in chasing hints that could bear fruit, and compelling hypotheses like these – which could save millions of lives – are not taken lightly. These studies were acted upon, with many huge trials of vitamins set up and run around the world. There’s also an important cultural context for this rush of activity which cannot be ignored: it was the tail end of the golden age of medicine. Before 1935 there weren’t too many effective treatments around: we had insulin, liver for iron deficiency anaemia, and morphine – a drug with superficial charm at least – but in many respects, doctors were fairly useless. Then suddenly, between about 1935 and 1975, science poured out a constant stream of miracles.

Almost everything we associate with modern medicine happened in that time: treatments like antibiotics, dialysis, transplants, intensive care, heart surgery, almost every drug you’ve ever heard of, and more. As well as the miracle treatments, we really were finding those simple, direct, hidden killers that the media still pine for so desperately in their headlines. Smoking, to everybody’s genuine surprise – one single risk factor – turned out to cause almost all lung cancer. And asbestos, through some genuinely brave and subversive investigative work, was shown to cause mesothelioma.

The epidemiologists of the 1980s were on a roll, and they believed that they were going to find lifestyle causes for all the major diseases of humankind. A discipline that had got cracking when John Snow took the handle off the Broad Street pump in 1854, terminating that pocket of the Soho cholera epidemic by cutting off the supply of contaminated water (it was a bit more complicated than that, but we don’t have the time here) was going to come