Several recent studies have looked at trends in the mortality differences between smokers and non-smokers. The studies have all produced remarkably similar conclusions – the excess mortality associated with cigarette smoking continues to increase resulting in a growing life expectancy difference between non-smokers and smokers. This is damning for the cigarette industry who have long claimed that increased usage of filtered cigarettes and low tar or “mild” formulations has resulted in a safer product. This simply doesn’t appear to be the case, and if anything, cigarette smokers are at a higher risk of dying from lung cancer, heart disease, and other smoking related illnesses than ever before.
Some of these studies are discussed in detail below.
The British Doctors Study
The British Doctors study was a prospective cohort study that ran for 50 years from 1951 to 2001. The study is notable in that it was one of first studies to provide conclusive evidence of a link between cigarette smoking and lung cancer, vascular disease, and other respiratory illnesses. Updated reports of the mortality experience of the cohort are published every 10 years with the final report published in 2004.
By the 1994 report, the researchers had noted an interesting trend emerge. The gap in life expectancy between non-smokers and current smokers appeared to be increasing. From 1951-71 the difference in life expectancy was 5 years however from 1971-1991, smokers were dying an average of 8 years earlier than non-smokers. By the 2004 report the gap had increased to 10 years.
Death rates for all causes among non-smokers dropped substantially across the study period and correspondingly life expectancies improved dramatically however death rates among smokers barely changed, despite substantial advancements in the treatment and prevention of most smoking related diseases.
The graph below shows age-standardized mortality rates for non-smokers and smokers across the 5 study periods. As can be seen from the graph, mortality rates halved in non smokers but actually increased by around 20% in current smokers.
In non-smokers, doctors born between 1851-1899 had a 45% of living to 80 and a 13% chance of living to 90. In non smoking doctors born between 1900-1930, the changes of living to 80 increased to 65% and chances of living to 90 had doubled to 26%. For smoking doctors born between 1851-1899, the chances of living to 80 and 90 were just 31% and 5% respectively. These figures barely changed in the cohort born between 1900 and 1930 with 32% and 5% living to 80 and 90.
The researchers estimated that as many as 2 in 3 smoking British doctors born in the 1920s would eventually be killed by their habit, much higher than the 1 in 2 estimate from earlier studies.
The authors wrote:”It is easy enough to understand why the mortality in nonsmokers should have improved, but why has it not done so in cigarettes smokers, who have generally experienced the same benefits of prevention and therapeutic medicine?”
The researchers put the widening gap in life expectancies down to the fact that early studies wouldn’t have captured the full extent of a lifetime of cigarette smoking because cigarette smoking didn’t become widespread until the 1920s. The earliest studies would therefore have included very few smokers who had smoked for more than 30 years.
It is unclear whether this would account for all of the increase in the gap between non-smokers and smokers, and in-fact data from other studies shows that even when duration of smoking is accounted for, the gap between non-smoking and smoking death rates is still widening.
Cancer Prevention Study I & II
CPS I & II were two prospective studies involving around 1 million American men and women each. CPS-I began in 1959 and CPS-II in 1982. The goal of the studies was to determine the effect of various lifestyle and environmental factors on the risk of developing cancer.
A 1995 study, published in the American Journal of Public Health, used data from CPS I (1959-65) & II (1982-88) to determine changes in mortality among cigarette smokers over the 20 year interval between the two studies.
The researchers found significant increases in the relative risk of death in smokers vs non-smokers for a variety of chronic diseases from CPS I to II. Mortality from all causes was 70% higher in smoking men and 20% higher in smoking women compared to non-smokers in CPS-I however in CPS-II the corresponding figures were 130% and 90% for men and women respectively.
The increases in smokers’ lung cancer death rates from CPS-I to CPS-II were particularly concerning. In lifelong non-smokers, the age-adjusted death rate remained relatively constant, decreasing from 15.7 to 14.7 per 100,000 per year in men and increasing from 9.6 to 12.0 per 100,000 per year in women. The lung cancer death rate for smokers on the other hand increased two-fold in men, from 187.1 to 341.3 per 100,000 per year, and six-fold in women, from 26.1 to 154.6 per 100,000 per year.
While increasing smoking intensity and duration explained part of the increase in lung cancer mortality over this period, smoking mortality in CPS-II vs CPS-I was still elevated by around 30% in men, and 150% in women, even after adjustment for these two variables.
American Journal of Public Health Study
A study, published online last month in the American Journal of Public Health used data from the National Health Interview Survey (NHIS) to calculate trends in mortality for smokers vs non smokers from 1987 to 2006. The researchers found that the risk of death for smokers increased by 25.4% over the 20 year period relative to non smokers. The relative risk of death for former smokers vs non-smokers also increased, but to a lesser extent. The researchers noted that the increases in the relative risk of death were not the result of increased smoking intensity or smoking duration.
There are many possible explanations for the increases in excess mortality due to smoking. It is possible that other environmental and lifestyle variables interact with cigarette smoking to raise lung cancer risks such as previous asbestos exposure or a declining intake of fruit and vegetables among current smokers (some studies have suggested a protective effect on lung cancer from a high fruit and vegetable intake). It is also possible that smokers under-report their current level of cigarette use due to increasing social stigma or that measures of current cigarette smoking do not accurately represent past smoking habits which may have been significantly higher.
What is apparent is that low-tar and filtered cigarettes have had little effect on smoking related mortality. Most studies show that smokers compensate for the reduced nicotine content of the cigarettes by inhaling more deeply, taking less time between puffs, and covering the filters. In some cases, this may actually result in greater exposure to the lungs for certain carcinogens.
Given all this information it is clear that smokers have not enjoyed the same reductions in all cause mortality that have occurred in non-smokers over the past 50 years and that if anything, the health risks of smoking have been underestimated due to reliance on older data.
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