Epidemiology and Chronic Disease
Epidemiology had played the dominant role in controlling the destructive epidemics but for a long time little attention was given to the non-infectious disorders: before 1950 practically nothing was known about the causes and prevention of major illnesses such as heart disease, lung cancer and chronic bronchitis.18 Many believed epidemiology was only concerned with infectious disease but that wasn’t the only reason for its neglect. A preference for laboratory research and animal experiments diverted attention from epidemiology and with it a true understanding of major diseases like cancer.
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(4) 143 years after soot had been identified as a human carcinogen by studying the diseases of chimney sweeps, laboratory researchers finally reproduced the findings by repeatedly painting a rabbit’s ear with tar.
Before the first World War, population studies had identified several causes of cancer:19 it was found, for instance, that pipe smokers were prone to lip cancer; that workers in the aniline dye industry contracted bladder cancer; and that radiologists often developed skin cancer. It was also known that combustion products of coal (soot and tar) could cause the disease, an observation dating back to 1775 when the English surgeon Potts identified soot as a carcinogen in chimney
sweeps. Attempts to reproduce Pott’s findings by experimenting on animals repeatedly failed20 but finally, in 1918, Japanese researchers produced cancer on a rabbit’s ear by repeatedly painting it with tar, a discovery that captured the imagination of the scientific world and changed the course of cancer research. According to British epidemiologist Sir Richard Doll, human observational data was now commonly dismissed because it was confidently assumed that laboratory experiments held the key to success.19 Crucial epidemiological studies like those of Percy Stocks at London University, who reported in 1933 that people consuming large amounts of fruit and vegetables were less likely to develop cancer,21 received little attention.19 Today we know that Stocks was right: recent epidemiological research has shown that a vegetarian diet, or at least one low in meat and rich in fruit and vegetables, can substantially reduce the risk of cancer.22
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