In the 1950s, Alice Stewart found that exposing pregnant mothers to X-rays doubled the risk of cancer in their children. Ever since, the physician and epidemiologist has argued that low doses of radiation might be harmful. It's a view that has put her at odds with governments, the military and the nuclear industry. This week, Stewart, who is 93, publishes new research supporting her claims. Michael Bond spoke to the maverick of radiation epidemiology and found her in fighting form.
What new evidence do you have to support your claims that low-level radiation could be dangerous?
Radiation safety standards are derived from studies of the A-bomb survivors of Hiroshima and Nagasaki. These studies were food for people supporting hormesis, the theory that a little bit of radiation can be good for you--that it stimulates the immune system. When it was found that a small number of the A-bomb survivors were living longer than they ought to, this was seen as proof that radiation had done them good. But we have new data that should put paid to that. We have proof that the A-bomb data have been wrongly interpreted. (See "Radiation: how safe is safe?")
What does your research show?
It shows that cancer was not the only effect of the A-bomb radiation. People died from immune system damage as well. Our paper also shows that the A-bomb survivors were not a normal, homogenous population. They were the best athletes--the top 10 per cent--and did not include the young and the old. This means that we cannot base standards of radiation safety on such an elite cohort.
Do you think that the authorities will now reassess the idea that radiation at low doses is not harmful?
I think this new paper will do it. But I don't think it will lead to an immediate reaction.
Why do you think your findings always take so long to be taken seriously? Take your work in the 1950s showing that a fetus exposed to X-rays has a higher risk of cancer. Or your findings in the 1970s that workers at the Hanford weapons complex in the US were getting cancer after supposedly safe levels of exposure.
The trouble is that I've always had a very small set-up, with only just enough money to employ people to do the research. I've never had a department that's out selling the message to other people. So it's been a bit slower than usual.
When it came to my work on X-rays, nobody wanted to believe it. X-rays were a favourite toy of the medical profession. But much more than that, it was just the moment when the nuclear industry was taking off. If we were right, the industry couldn't develop properly.
Your work has tended to attract a lot of criticism from scientists, one of whom is the leading epidemiologist Richard Doll. Why do you think he doesn't like your work?
I moved to Birmingham University for that reason. I knew that if I stayed at Oxford I would always be under the thumb of Doll. But that is the extraordinary thing. I can have reason to be angry with him because he was powerful and I was weak. He can have no reason at all to be angry at me, and yet he must resent me for some reason. Something irks him about me, and I'm conceited enough to think he suspects I'm a better epidemiologist than him. Now, he will tell you he has never had any quarrel with me at all.
Doll has criticised your methodology on the Hanford Studies. Why?
He's criticised my methodology from the word go. I don't know why. He's even criticised the mathematics of George Kneale, my statistician. But Doll doesn't know a fraction of the mathematics that George knows. I don't know what he means when he says our method is wrong, but he should be called to account.
The main objections to my X-rays study was that the mothers were lay informants --that they weren't scientists, and they could have made up stories. We always knew there were weaknesses in our story. But we'd done our best to check this through the hospitals where they had their X-rays.
You've been described as "an avowed opponent of the nuclear industry". Are you?
Well, I've never avowed it to anybody. But if by the nuclear industry you mean the war and energy industries, then yes I'm against it. If you mean, do I think we should stop using X-rays, then no, but you must use them knowing they are a dangerous toy. I think the medical profession has quite a lot of uses for it. Take, for example, irradiated food. If this was going to prolong the life of food that you could send to a country to save it from starving, it would be excellent. But what you've got to be careful of is not to allow industry to indiscriminately use this radiation and to find it's going down your back drains.
I'm automatically against it for war, and you have to remember that the nuclear military and energy industries have always been far more intimately connected than most people realise.
The discovery that made your name in 1956 was that a fetus exposed to an X-ray is twice as likely to develop cancer within 10 years as one that is not. Did this finding come as a complete surprise to you?
Yes. We weren't particularly looking for a link between cancer and X-rays. We were comparing the medical records of children who had died from leukaemia with those of healthy children from the same regions. And in the questionnaire, we had asked mothers if they'd been X-rayed. It looked to me as if there had been something before birth that produced a little epidemic at a certain age group that never repeated itself. But the risk was so small that if we'd tackled it any other way we'd never have discovered it.
We were lucky, but it wouldn't have been thought of by someone who hadn't had some experience of medicine, and it might have been wrongly interpreted. So if you hadn't found the link it might have been another 20 years before someone else did?
No, not 20 years. To this day we would be thinking X-rays were safe. This is because, as I've indicated, the A-bomb survivor studies from Hiroshima and Nagasaki, which was the only other study on this, was saying it was safe, and this would have been considered satisfactory to the point where everybody would have been quite happy about X-rays.
How much do you think being a woman helped or hindered your career? When you first walked into the lecture hall as a medical student at Cambridge in 1925 you were met with 200 male students stamping their feet at you.
I'm sure my sex made a tremendous difference. But thanks to my family--my mother was a doctor--and thanks to the war, rather than being a crippling difficulty it actually proved to be rather a helpful one. I found I was constantly thinking of things in an unusual way. I didn't expect to be allowed to get to the top rung, which is something a man would expect, and so perhaps that made it easier to stay with a subject that wasn't very popular.
Has that bothered you?
Not at the time, but in retrospect I think it's the one thing I rather regret . . . that I should have pressed for something more. But I was stuck, I could only do one or other of two things: I could either be fighting the battle for women or I could be getting on with my job. I couldn't win both. And I chose to go on with my job. But I think a braver person might have done something about it.
Were you ever bitter about being sidelined?
No, I think I personally had everything to gain by it. It's always worked in my favour. An element of uncertainty is always a good thing. It's been a constant help. You need some resistance and criticism to bring out the good work. One of the reasons it's been so interesting for me is that no one has ever lost interest in what I've said about radiation. They may despise me, they may hate me, but the problem is there and will stay there if nobody's solved it.
Most people think about cutting back on work when they reach seventy. Did you miss out on anything by carrying on in your nineties?
I stayed working because I was enjoying it, and it was all voluntary. It became obvious early on that we had hit on something that was going to take more than a lifetime to resolve. It wasn't just the radiation thing that interested me. I was really interested in where the other cancers were coming from. You need to follow it for a long time.
Who will carry on your fight in the radiation debate?
I've got a voice in the next generation in Steve Wing and his department at the University of North Carolina at Chapel Hill. Mind you, they're going to make life difficult for them, with grants and everything. People in the nuclear industry will do their very best to stop it. But I'm a great believer that in the end, they'll get caught up in their own machinations and the truth will emerge from an unexpected quarter.
"A bomb survivors: factors that may lead to a re-assessment of the radiation hazard", International Journal of Epidemiology, volume 29, no 4 (4 August 2000) The Woman Who Knew Too Much by Gayle Greene, University of Michigan Press, £19.99, ISBN 0472111078
Radiation: how safe is safe?
The A-bomb database--a record of the health and mortality of the survivors of the Hiroshima and Nagasaki atomic bombs--is considered the gold standard when assessing the health risks of radiation. Alice Stewart, however, has spent much of her career arguing that it cannot be trusted. Her latest research, published this week in the International Journal of Epidemiology (vol 29, no 4), strengthens that argument.
The database is used to compare the mortality rates of A-bomb survivors with other Japanese citizens born at the same time. The results have always been the same: people exposed to low doses do not have a higher than average risk of cancer. Stewart says these conclusions are unreliable because the bomb survivors are not truly representative of Japanese society.
In her latest paper, she focuses on the 2,600 people who suffered severeradiation injuries even though most received only a small radiation dose. In particular, she wanted to compare their incidence of cancers and other diseases with that of around 60,000 low-dose survivors who did not suffer from serious injuries.
Stewart found the minority group had a much higher incidence of cancer and heart disease. She says these findings were reported to the European Parliament two years ago (see New Scientist, 28 February 1998, p 12) but that the assembly, curiously, decided not to make them public.
Stewart's detractors have pointed to a series of studies showing that certain survivors of the Hiroshima and Nagasaki bombs lived slightly longer than people who had not been exposed.
But research published in The Lancet (vol 356, p 303) at the end of last month casts doubt on these results. Researchers from the Radiation Effects Research Foundation in Hiroshima examined the effects of radiation on the 120,000 A-bomb survivors and found that people who received low doses did not live longer than average.