In the 1920's lung cancer rates were rising in many countries. At that time this was popularly attributed to factors like air pollution, damp climate, exhaust from motorized vehicles and carcinogens from the tar used to make roads. Then, there was no definite evidence that smoking habits were linked to malignant growths in the lungs.
Along came a British doctor, Sir Richard Doll, who started the world's first major medical cohort study to find out what was causing the huge surge in lung cancer in Britain. He recruited 35,000 British male doctors into his prospective cohort study. There were two things going for recruiting doctors as participants:
It was relatively easy to trace them through the years as doctors need to stay registered to practise.
Being doctors and very likely having good access to medical care, their reported information was very likely to be medically accurate.
He said, “I personally thought it was tarring of the roads. We knew that there were carcinogens in tar. It wasn't long before it became clear that cigarette smoking may be to blame. I gave up smoking two-thirds of the way through that study.”
The results from Sir Richard Doll's study influence our personal habits (to smoke, to quit or not to smoke), and national policies (e.g. ban on smoking advertisements, ban on smoking in certain public areas, pictures on cigarette packs). Now if we choose to smoke, it is with the full knowledge that it is linked to an increased risk for lung cancer.
It's hard to believe in 1948, doctors had no idea that heart disease was in any way linked to high blood cholesterol. The fact that blood cholesterol measurements are a regular part of health screening today is thanks to the Framingham Heart Study in Massachusetts, United States, an ambitious project in health research in 1948. Starting with just 5,209 participants (all volunteers), that study has revolutionized the treatment of heart disease by linking it with hypertension and high cholesterol levels.
As it happens, in 1971 a further 5,100 participants - children of the original cohort and their spouses – were recruited to carry this study into a second generation. The study is no longer just focused on heart disease, it now includes cancer, dementia, arthritis, osteoporosis and hearing and eye disorders. A staggering 1,000 scientific papers have been published from discoveries made through the study of this cohort – giving us some inkling of the real-life impact this study has on our lives.
Showing strong support, 3,900 grandchildren of the Framingham Heart Study's original participants - enrolled in the Framingham “Third Generation Study” in 2002. Key goals in this third-generation study are to identify new risk factors for heart, lung, and blood diseases, identify genes that contribute to good health and to the development of heart, lung, and blood disease, and to develop new imaging tests that can detect very early stages of coronary atherosclerosis in otherwise healthy adults.
This study started in 1992, spanned 10 European countries and involved more than 500,000 participants. It discovered that people who have a healthy intake of fruit and vegetables have a lower risk of developing cancers of the digestive system, lungs, bladder, kidney and ovary. It established a positive link between low dietary fibre and colorectal cancer.
This study also showed that smokers with a high fruit and vegetable intake, ran a 40% lower risk of getting lung cancer than their fellow smokers who did not share a similarly high-fibre diet. Of course the study emphasized that smokers who quit, lowered their risk for lung cancer, even further.
This is said to be one of the most significant studies ever conducted on the health of women. It started in 1976 with the primary aim to investigate the potential long term consequences of the use of oral contraceptives, and involved 122,000 American nurses.
The Nurses' Health Study II was set up in 1989 to study oral contraceptives, diet and lifestyle risk factors in a population younger than the original Nurses' Health Study cohort, and involved over 116,000 American nurses.
Both phases of this study continue to investigate risk factors for major chronic diseases in women.
This study, which began in 1982 and involving 33,223 male medical doctors between 40 and 84, examined if aspirin and beta-carotene are useful in the prevention of heart disease and cancer, respectively.
It was unusual for being the first large, randomised trial conducted entirely by mail – a trial by mail, so to speak. Usefully as a group, physicians would report their medical histories and health status more accurately than participants drawn from a general population. They would also be more likely to identify possible side effects of the study agents. For the collection of blood samples, participants were given kits containing prepared Vacutainer tubes, cold packs for mailing, and prepaid shipping packs.
The trial's Data and Safety Monitoring Board stopped the aspirin arm of this study several years ahead of schedule because it was clear that aspirin reduced the risk of first heart attacks by 44%. Results from the beta-carotene arm were equally important - 13 years of supplementation with beta-carotene produced neither benefit nor harm. These results demonstrated that beta-carotene alone was not responsible for the health benefits seen among people who ate plenty of fruits and vegetables. More than 170 other findings have emerged from the trial so far.
A second randomised trial, the Physicians' Health Study-II, started in 1997 and is now testing the balance of benefits and risks of three other widely used, but as yet unproven, supplements for the primary prevention of cardiovascular disease, cancer, and age-related eye disease - vitamin E, vitamin C, and a multivitamin. 14,642 male medical doctors aged 50 years and over, receive a 12-month supply of study pills in calendar packs and an annual follow-up questionnaire which includes questions about compliance with the study treatments, use of non-study medications, occurrence of major illnesses or adverse effects, and other risk factor information.
Between 1993 and 1998, 160,000 American women, aged 50-79 were recruited into this study. It researched the most common causes of death, disability and poor quality of life in post-menopausal women, such as cardiovascular disease, cancer and osteoporosis. Different part of this study looked into the effects of hormone, dietary modifications and the effects of calcium and vitamin D.
This was the study that shocked the world by finding out that hormone replacement therapy increases rather than reduces a woman's risk for suffering a heart attack.