Gail Vines meets Alice Stewart, the pioneering epidemiologist and heroine of the anti-nuclear movement.

In the mid-1950s, the pioneering epidemiologist Alice Stewart showed that the practice of X-raying pregnant women was causing leukaemia and other forms of cancer in children. It was the first evidence that low-level radiation could harm human health. Yet, in the climate of techno-optimism that dominated the 1950s, many of Stewart's peers did not believe her data and did their best to refute them. Her popularity did not improve when she began uncovering new evidence that low-level radiation was damaging the health of workers in an American nuclear reprocessing plant that produced plutonium for nuclear weapons. Today, she remains a controversial figure, with friends and foes scattered throughout the world. At 88 Stewart is still at the bench and still publishing papers to confound her critics.

"I was unpopular at first because undoubtedly X-rays were a favourite toy of the medical profession," she says. "And, of course, I became unpopular when I focused on a nuclear weapon manufacturer. But you can't blame yourself for that." A heroine of the anti-nuclear movement today, she is keen to stress her impartiality. "If the data had gone the other way I would have been just as strong."

Stewart "retired" from Oxford some 20 years ago, where she was reader of social medicine. But she immediately set up a new base at Birmingham University, where she still works with statistician George Kneale. Every weekday she walks to her office in the medical school and gets on with the analyses.

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Where did she get the courage to carry on despite the hostility her work has long inspired? "People often ask me that," she muses, "and I think it's slightly to do with being a woman."

When Stewart - already the youngest woman ever to be made a fellow of the Royal College of Physicians - became head of a pioneering department of social medicine soon after the war, the Oxford medical faculty had already decided there was "no future" in public health epidemiology. But Stewart refused to go. Starved of funds, status and influence, she dug her heels in. "I became head of this department that was deprived of everything. If I'd been a man, I would never have stood it - I would have gone. The prospects were too bad, the pay was too low. But being a woman I didn't have all that number of choices. I have always found it difficult to spend money."

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Daughter of two doctors, Stewart was encouraged to seek a medical career. But she found her fellow Cambridge medical students "absolutely shocking". "There were four women and 300 men in my class. As I came into the lecture theatre and took my first step the men started to slowly stamp their feet in unison. I had to walk down the steps, to run the gauntlet, to sit on the front row with the other girls, along with one other person - I would never make friends with any medical student; I was having nothing to do with these 'scum', I said to myself."

It set the pattern for Stewart's later life. Her husband and friends were to come mostly from the arts or politics, rather than from medicine. She applied for hospital posts, but now married to a schoolteacher, and with two children, she found it difficult to land good jobs. The outbreak of the second world war was her salvation. "Suddenly I was persona grata, as I couldn't be called up. I was being offered jobs that normally would only have gone the way of men." Arriving at the Nuffield Department of Clinical Medicine in Oxford, she had her first taste of research.

She tackled a problem that worried both the Medical Research Council and the War Office: how to safeguard the health of factory workers whose job it was to fill shells with the toxic and explosive chemical TNT. It was to be her first foray into the still embryonic field of "social medicine".

Characteristically, she adopted a novel approach to the problem. "I felt I didn't know enough about the thing, and the only way to do it would be to go and fill the shells myself, and then I might have some understanding of what it was about." She had biochemical tests done on herself before and after. Then she began to recruit student volunteers to work in the factories during the long vacation under agreed conditions. "They could do their war work this way and be paid for it, in return for the occasional blood test." The work was a great success, revealing ways in which work practices would be altered to limit workers' exposure.

After this triumph, she was popular with the Medical Research Council, which commissioned her to do three or four similar sorts of investigations during the war. Stewart says her "semi-ingenuity in thinking up things" won her a fellowship to the Royal College of Physicians. "I was the first woman under 40."

At the end of the war John Ryle, who had what is today called a holistic view of medicine, decided that "public health" lacked a proper university basis. He put his name to the first department of social medicine in Oxford. "Before the war, medicine was more or less a grocery business; you sold your drugs to those who could afford them. But the advent of war showed that doctors have a responsibility to the whole nation and need to find the answers to questions that are relevant to public health."

Ryle asked Stewart to join him, but soon after, he died, "unfortunately just as the medical faculty of Oxford was regretting founding the department". The decision to close the unit was rescinded only for fear of offending a living patron, Lord Nuffield. "I was put back in charge but in very, very mean conditions," says Stewart. She began to look for something new to study, and settled on leukaemia, when her statistician colleague David Hewitt noted that there was something peculiar going on in children. He showed that there was an early peak of mortality from leukaemia between the ages of two and four.

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"I said, let's go to the mothers of the children who died of leukaemia and other sorts of cancer and get their story. I suspected that the leukaemia peak was caused by something that was happening prenatally, and that the mothers might have collective memories of that which the doctors hadn't noticed." But when Stewart took this project to the MRC, she was turned down "on the grounds that leukaemia was too rare and you couldn't organise the survey and one thing or another". With Pounds 2,000 scraped together from a charitable trust by a supportive colleague, she set out to do the project anyway. Stewart convinced the medical officers of each local authority to interview the mothers and set up a control group of children from the same age and area. "We could see in the first 37 completed forms there was one obvious difference: the mothers of children with all forms of malignant disease had been X-rayed before giving birth twice as often as matched controls. That set the jackpot going and roughly has kept me in the business of low-level radiation ever since."

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Stewart's preliminary report came out in 1956, as she turned 50, and caused a considerable stir. "But lots of people chipped in saying we must be wrong, including the people on the MRC committee that had turned us down. So we said, we'd better go on." Stewart and her colleagues begin to survey all the children born in a given year and to continue to keep track of their health, year after year, for ten years and more. "For years and years ours was the only evidence of low doses of radiation having a cancer effect."

Throughout this period, American funding bodies provided the bulk of the modest "glue money" that kept the childhood survey going. Stewart happened on this source of funds almost by chance. In the 1950s a visiting American epidemiologist arrived late at her office, saying he had thought Keble College, across the road, was her establishment. "I laughed and said we don't go that big here, I'm lucky enough to have one room." He suggested applying to the United States for funds, and sent her the documents. At last, after the forms had languished in her in-tray for some weeks, she asked for Pounds 5,000. She got it and the grant kept being renewed.

Controversially, Stewart was never awarded a university professorship, but she was made a professorial fellow of Lady Margaret Hall. International renown and the chance to travel came after the childhood cancer report. She became "rather well known" and began to establish links with American epidemiologists working on radiation exposure among workers at the Hanford nuclear plant in Washington state and on the A-bomb survivors. After the Three Mile Island accident in the US in 1979, she and George Kneale won a Pounds 1.2 million grant from the Three Mile Island Public Health Fund, which has been funding their work since the mid-1980s.

Against the mainstream, Stewart and Kneale argue that A-bomb survivors are not a reliable source of risk estimates for cancer. "Time and again you read that A-bomb data are the gold standard, and anything that differs from that is wrong." As a result, few researchers in the field are yet prepared to believe Stewart's and Kneale's analysis of the Hanford workers' data, which reveals an increased cancer risk even at low levels of exposure.

She and Kneale argue that their critics are pooling different data illegitimately and neglecting the effect of age on health risks. The critics by and large ignore her. "I don't think they're wicked, I think they've blinded themselves, they've got tunnel vision."

Her secret weapon, apart from her longevity, she says, is her "latent conceit: I know that I am going to be right. I have known this for some time. It may not happen in my lifetime - in fact, it probably won't - but it will be found that we were on the right track. You'd be surprised how comforting that is."

She sees conventional ambition as a snare and delusion. "I like to think I stand for something, and that is, don't be afraid not to get to the top, it's a most uncomfortable position. I've always had enough money to do my work, never big grants, but always enough."

Her favourite quotation comes from Webster's Duchess of Malfi: "Glories, like glow-worms afar off shine bright. But looked to near, have neither heat nor light." She chuckles: "Don't you think that's lovely? I laugh about it, and say tomyself, yes, those glow-worms, I don't really mind about them."

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