The
Research of the Relation between Mortality and Smoking:
In the recent decades, the researches of basic epidemiology have become an important source of information and recommendations in the field of public health. For the students of medical disciplines it is important to conduct their own research in the field of interest, and analyze the papers on other researchers of the field. As a part of the assignment, I intend to analyze the article dealing with smoking habits and their influence on the lifespan of humans.
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The hazardous impact of smoking on the health and life expectancy of people have become an issue of great concert in the second part of the XX century. The research of the relation between mortality and smoking by Richard Doll et al., published in British Medical Journal in 2004, provides an insight into the problem and a scientific proof of the harmful effects of smoking based on a 50-year observation of certain population.
Summary of the study, main goals, subjects and results
“Mortality in relation to smoking: 50 years’ observations on male British doctors” was designed to determine the impact made by smoking on men who formed the habit at different periods. The second objective focused on the specific benefits gained upon smoking cessation at different ages.
The research concentrated on the smoking habits and cause-specific mortality of the male British doctors and lasted 50 years (from 1951 to 2001).
The results obtained by the scientists have shown that smoking caused excess mortality mainly through vascular, respiratory and neoplastic diseases. The life expectancy of smokers versus lifelong non-smokers (for men born in the first three decades of the XX century) was a decade less for the former. As for the cessation effects – giving up smoking somewhere in the ages 30 to 60 gained from 3 to 10 years of life expectancy. In fact, cessation at 30 almost avoided the hazard of age specific mortality, while cessation at 50 has halved it. For those born in the first decade of the XX century, cigarette smoking doubled the age specific mortality rate, while for those born in the 1920s the hazard was tripled.
Also the longevity has been improving substantially in the course of the XX century. But the statement holds true only for the non-smokers, while for the persistent cigarette smokers the life expectancy is distressing – about half of them are killed by the habit. A quarter dies before reaching 70 (Doll, 2004).
The prospective study of the smoking effects on British doctors that lasted for 50 years is one of the first truly extensive studies on the topic, because it enabled us to see that the full effect of large increase in cigarette smoking by young people on nation mortality rate can take more that a half of the century to mature.
The decision to conduct the study among the doctors originated from the idea that the latter were able to describe their smoking habits accurately and their medical register would provide information on their mortality, with the causes accurately certified.
According to the paper, the first country in the world to experience a large increase in male lung cancer from cigarette smoking was Britain. The rate of lung cancer affecting the cigarette smokers born in the XIX century were much lower than that affecting men born in Britain in the first three decades of the XX century.
The strengths and limitations of prospective cohort designs
The researchers use the prospective (double) cohort study with internal control, with the cohort exposed smoking (quantified amount) versus non-smokers, with an exposure outcome of lung cancer and death. The periodic F/U surveys and review of death records enabled the researches to obtain the following results on dose-response and increased risk with any smoking.
It is quite a valuable fact that the cohort design in focused on birth dates and smoking-non-smoking exposure. Such focusing enables to analyze the influence of birth decade and smoking habits on the longevity and health.
The cohort studies enable to research health patterns among large groups of diverse individuals, follow them for long periods, and provide information on various (including rare adverse events) outcomes. However, the evidence needs to be balanced against concerns about the validity of the given evidence.
If we analyze the possible limitations of the cohort design, we should pay attention to the fact that although the cohort was quite controllable, the method of obtaining information (through questionnaires) had certain drawbacks. First of all, the participants, even though they were doctors themselves, could have provided inaccurate information on the levels of cigarette consumption or other valuable parameters that have influences the findings.
The duration of the experiment has also made certain impact on the results no matter how conscious the participating doctors were. It is known to us that 17 of the doctors who were struck off the medical register for unprofessional conduct, while 467 requested (mostly in the fifth decade of the study) no further questionnaires, and 2459 were known to be alive but living abroad on 1 November 1971. All of the participants mentioned above have been withdrawn from the list. Also, the mortality among 248 doctors is untraced (usually since the 1970s)). Those withdrawn before the end of the study or untraced are included in the analyses of mortality until the time of withdrawal or until contact was last made – and this brings certain distortion to the findings. Validity of results is highly sensitive to losses to follow-ups.
And finally, those who failed to complete a particular questionnaire could generally be traced for mortality and so continued to be analyzed according to their previously reported smoking habits, which might have caused certain inaccuracy in correspondence to the facts.
And although technically the data provided does not miss any important values, the information is still questionable in terms of employing it on the whole society. The question whether the cohort is representative for the British society or worldwide is among the primary issues for the research to be considered a valuable source of data.
Cohort studies generally start with exposures and then follow the cases through time, for the outcomes. Prospective double cohort design is used when exposures need to be measured precisely and the outcomes are relatively common.
The main limitations of this type of research design are that it is inefficient for study of rare outcomes, unless the attributable-risk is high for the exposure. Moreover, prospective cohort design is often can be nearly as resource-expensive as randomized controlled trials. It is also highly dependent upon the adequacy of records.
An alternative study could have been a combination of national statistics with several case-control studies, like the “Smoking, smoking cessation, and lung cancer in the UK since 1950” research (Peto, 2000).
When selecting cohort for long-term prospective studies it is important to consider the conformity of the selected cohort to the overall aim of the research, the availability of information and the complications to the research due to lack of data or other factors influencing the group.
The common features and fundamental differences of the cohort are also of great importance when selecting the cohort – issues like heredity, environmental conditions of the residence location, working conditions, stress levels, etc might be the confounding factors to the study.
The applicability of results for modern society
The cohort selected for the research is limited to those born in the late XIX and early XX centuries. The patterns of life and health for the following generation has been influenced by various factors like the change of environmental conditions, types of work, less physical training and extensive stress due to work overload. According to the comparatively recent studies of cigarette smoking patterns among young adults aged 18-24 years in the United States, compared with those currently enrolled in school, young adults not currently enrolled in school were more than twice as likely to report current and daily smoking (Lawrence, 2007). Blue-collar and service workers were more likely to report current and daily smoking or even heavy smoking, compared with white-collar workers. Compared with those not in the labor force and those reporting an annual household income of $20,000 or more, the unemployed (those in the labor force but not currently working) and those reporting an annual household income of less than US$20,000 were more likely to report current, daily, and heavy smoking (Lawrence, 2007). Therefore, the level of income and the type of daily activities might have substantial influence upon the levels of cigarette smoking.
The results of the study are less applicable to a cohort of young smokers in 2004, due to the changes of consumption patterns and overall living conditions.
If a similar cohort Doll has selected for his studies started now, the results might be influenced by additional factors like the recent change in UK cigarette-caused mortality pattern. Britain is now experiencing the most rapid decrease in the world in premature deaths from tobacco: from 1965 to 1995 annual UK cigarette sales fell from 150 billion to 80 billion, and there was a moderate reduction in the hazard per smoker due to a threefold reduction in the machine-measured tar delivery per cigarette. Over the same period, annual UK tobacco deaths in middle age decreased from 80,000 to 40,000, and continue to fall rapidly. Over the past few years, the UK male death rate at ages 35-69 for lung cancer has been decreasing at the rate of 40% per decade (Peto, 2000). UK mortality in old age from tobacco should also decrease substantially, the researchers believe (Peto, 1994). As the consumption patterns change and the health issues are addressed more actively, the results of the given study are becoming less applicable to the society of the developed countries, though the findings might still be of great value to the developing countries that are on average 40 years behind Britain and the United States.
Conclusion
The need for substantial analysis of health patterns has made the researches of basic epidemiology become a valid source of information for the scientists and practicing medical specialists. Despite several limitations of the prospective cohort designs, this type of research is getting more and more popular among the scholars analyzing various health problems of the modern society. Although prospective cohort designs generally take a lot of time, their findings are often applicable even several decades later, especially if the research has been conducted in developed countries. The developing countries tend to have the similar pattern with a delay of a couple of decades.
The research “Mortality in relation to smoking: 50 years’ observations on male British doctors”, by Richard Doll et al., published in British Medical Journal in 2004, aimed at determining the relation between mortality and smoking. The results are indeed interesting and useful for the further studies on the subject as well as for presenting the evidence of hazardous influence of smoking on the health and the lifespan of humans.
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