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Smoking

Sixty years ago, smoking was generally regarded as innocuous; now it is recognised as the main cause of lung cancer, the world’s most common fatal cancer. Pioneering MRC researchers helped establish a link between smoking and cancer 50 years ago. Over several decades, they identified the full hazards of smoking and the benefits of stopping, which has influenced public policy and behaviour. This has prevented millions of unnecessary deaths and culminated in a Government ban on smoking in enclosed places that will save the country billions of pounds.

In 1947, the MRC held a conference to discuss the possible causes of the ‘phenomenal increase’ in deaths from lung cancer in the UK. Sir Ernest Kennaway, the Secretary of the MRC, and other scientists suggested that tobacco, particularly when smoked in the form of cigarettes, might be responsible. MRC scientists Sir Richard Doll and Sir Austin Bradford Hill published a preliminary paper in 1950 that suggested a relationship between tobacco smoking and cancer1, consistent with the results from studies in other countries that were also analysing the effects of smoking.

A hunch confirmed

The MRC studies, however, stood out because of their size and precision. In 1951, Doll and Hill began a study of 40,000 British doctors who were born between 1900 and 1930. Doctors were chosen for the study because they were a relatively simple group to follow for a long period - through the General Medical Council’s register. They were asked about their smoking habits and those who replied have been tracked ever since to see what illnesses they died of. Among the first results, a paper published in 1956 showed that the death rate from lung cancer among heavy smokers was 20 times the rate in non-smokers, indicating beyond doubt that smoking causes lung cancer2.

Over the next half-century, MRC researchers collected more and more data and the extensive dangers of smoking gradually emerged. In 2004, Sir Richard published follow-up results from his original study, showing that the overall risks from smoking were even greater than originally suspected and that, on average, smoking lowered life expectancy by 10 years3. He and his colleagues found that around half of those who smoked were killed by their habit. They also showed that stopping smoking at ages 30, 40, 50 and 60 increased life expectancy by around ten, nine, six and three years, respectively.

Compared with non-smokers, smokers are at high risk of dying from many diseases: about a twenty-fold higher risk from lung cancer, a ten-fold risk from chronic obstructive airways disease and a one-and-a-half to three-fold risk from coronary heart disease4. Smoking also increases the risks of strokes and cancers of the mouth, bladder, liver, pancreas, kidney, stomach and cervix.

Smoking and behaviour

This work – predominantly MRC-led – resulted in national public health campaigns and a dramatic reduction over the past 50 years in the number of people who smoke. Currently, 26 per cent of men and 23 per cent of women smoke, according to the General Household Survey. These compare with 51 per cent of men and 42 per cent of women in 1972, and 59 per cent of men and 43 per cent of women in 1961. Smoking peaked in 1948 for men at 82 per cent and in 1966 for women at 45 per cent.

According to 2000 data, 115,000 people a year die from smoking; half of the number in the early 1970s when twice the number of people smoked as they do now. Sir Richard Peto at the Clinical Trials Service Unit in Oxford, which is partly funded by the MRC, found that smoking-related cancer deaths among middle-aged men dropped dramatically after people became aware of the dangers and stopped smoking in the 1970s, while the rate of cancer deaths not related to smoking stayed the same (see graph).

There has also been a huge drop in the number of cardiovascular deaths that has coincided with the reduction in numbers of people smoking since the late 1960s. The risks of heart disease decrease even more quickly than the risks of cancer after quitting. After one year off cigarettes, the excess risk of heart disease caused by smoking is reduced by half.

The benefit of bans

As well as influencing behaviour, smoking research is finally having an impact on public policy. There have been Government bans in England, Scotland, Wales and Northern Ireland on smoking in workplaces and public places, after sustained exposure to passive smoking was also shown to be harmful – non-smokers who are exposed to second-hand smoke at home or at work increase their risk of developing lung cancer by 10-30 per cent5.

According to the Government’s draft regulations, the England ban is estimated to bring in net benefits of up to £2.1 billion a year. This is due to the large number of lives saved – a year of life is estimated to be worth £30,000 – reduced NHS expenditure, more productive time from reduced exposure to second-hand smoke, and fewer fires and cleaning costs. The annual cost of employing smokers is considerably more than that of non-smokers, principally due to decreased productivity as a result of cigarette breaks – this was quantified in Canada 10 years ago6. Adjusting for inflation, the increased cost per employee is over £1,700 a year.

The effect of the Scotland ban has been quantified in the first year after the smoking ban has come into force. There has been a 17 per cent fall in admissions for heart attacks, which compares with an annual reduction in Scottish admissions for heart attack of 3 per cent per year in the decade before the ban. This figure was one of a number of results presented at an international conference discussing the impact of the smoking ban on Scotland’s health, air quality and society. Scientists also presented evidence that there was nearly a 40 per cent reduction in exposure to secondhand smoke (measured from saliva samples) among around 600 adult non-smokers7.

Scientists funded by Cancer Research UK in Warwick showed that English non-smoking workers in the hospitality industry had only a quarter of the cotinine – a by-product of nicotine and an indicator of tobacco smoke exposure – in their saliva in August 2007, just after the ban, compared with what they had two months before.

References

1. Doll & Hill (1950). Smoking and carcinoma of the lung; preliminary report. BMJ, 2, 739.

2. Doll & Hill (1956). Lung cancer and other causes of death in relation to smoking; a second report on the mortality of British doctors.
BMJ,
2, 1071.

3. Doll et al. (2004). Mortality in relation to smoking: 50 years’ observations on male British doctors. BMJ, 328, 1507.

4. Peto et al. (1992). Mortality from tobacco in developed countries: indirect estimation from national vital statistics. The Lancet, 339, 1268.

5. US Surgeon General (1986). The health consequences of involuntary smoking (Maryland, USA, Department of Health and Human Services (CDC), 87.

6. Lok. Smoking and the bottom line (1997). The costs of smoking in the workplace. Ottowa, The Conference Board of Canada.

7. Haw & Gruer (2007). Changes in exposure of adult non-smokers to secondhand smoke after implementation of smoke-free legislation in Scotland: national cross sectional survey. BMJ, 335, 549.

MRC, September 2006, updated October 2007

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