The absence of epidemiological data allowed mistaken theories based on animal research to flourish. It also misdirected vast resources into areas irrelevant to most human cancers. Although we now know that only about 5% of US cancers are associated with viral infection,23 scientists once confidently believed that most, if not all, cases were caused by viruses, a view derived from experiments on animals where it is easy to transmit the disease in this way.24 It was even argued that because breast cancer in mice can be produced by a virus, women should not nurse their babies in case a corresponding infection is transmitted in the motherís milk!25 With the origin of breast cancer differing even between rats and mice, it is hard to see how such views could ever by taken seriously.
© Hulton-Deutsch Collection
(4) Epidemiological studies of the notorious London Smog of 1952, connecting ill-health with pollution, led to the Clean Air Act of 1956.
Fortunately, following the second World War, interest in the epidemiology of non-infectious disease was re-awakened. The most striking discovery connected smoking with lung cancer.
By 1954, when Richard Doll and Bradford Hill published their famous investigation into the smoking habits of British doctors,8 there were already more than a dozen population studies linking cigarettes and the disease. In 1951 Doll and Hill had sent questionnaires to 59,600 physicians on the British medical register requesting information about their smoking habits. The 40,000 doctors who responded were divided into non-smokers and three groups of smokers, depending on the number of cigarettes consumed. The causes of any deaths were then recorded over the ensuing 29 months. The study revealed an all-important dose-response relationship with the chances of developing lung cancer increasing with the number of cigarettes smoked. Later studies by the same researchers found that doctors giving up the habit substantially reduced their risks of becoming ill.26 Further population studies subsequently linked many other types of cancer to cigarettes so that today, smoking is held responsible for 150,000 US cancer deaths a year.
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