A second study, also published in the Jan. 24 issue of the New England Journal of Medicine, found, for the first time, that women smokers are dying just as quickly – and from the same conditions – as men who smoke.
"The relative risks of death from lung cancer, chronic obstructive pulmonary disease, ischemic heart disease, any type of stroke, and all causes are now nearly identical for female and male smokers," Dr. Michael Thun and his colleagues wrote (N. Engl. J. Med. 2013:368:351-64). "This finding is new and confirms the prediction that, in relative terms, ‘women who smoke like men die like men.’ "
Dr. Thun, an epidemiologist with the American Cancer Society, and his colleagues drew their three study cohorts from seven national studies and databases. The entire study group comprised 1.32 million women and 899,000 men. Two of the cohorts were considered historical, covering 1959-1988; five were considered contemporary, covering 2000-2010. The participants’ ages by the end of each group’s follow-up period ranged from 50 years to more than 80 years.
For never-smokers, the analysis showed a general overall improvement in mortality between the historical and contemporary cohorts. But smokers did not enjoy this benefit. Between the historical and contemporary cohorts, all-cause mortality was 50% higher in smokers than in nonsmokers.
Again, women were particularly at risk, the investigators noted. "In contrast, there was no temporal decrease in the all-cause death rate among women who were current smokers and there was a 23.6% decrease among men who were current smokers. ... The risk of death from lung cancer among male smokers appears to have stabilized since the 1980s, whereas it continues to increase among female smokers."
Dr. Thun and his associates also found the threefold increase in the risk of death between smokers and never-smokers. Their data determined that at least two-thirds of these deaths were directly associated with smoking, including ischemic heart disease, all other heart disease, stroke, and lung cancer.
A comparison of nonsmokers and smokers within all the time cohorts showed that the highest risks of death for most disorders occurred from 1982 to 1988. Since then, the mortality risks have declined and stabilized but still remain elevated compared with never-smokers. The lung cancer mortality risks were strikingly evident, the authors said: a relative risk of 25 for both men and women.
In contrast to the stabilized rates of other diseases, the mortality risk of chronic obstructive pulmonary disease has continued to increase in smokers. The biggest jump affected smokers older than 55 years and occurred after the 1980s period. The overall COPD mortality risk in the 2000-2010 cohort was more than double that of the 1980s (RR 10 vs. 25.6). The risks were similar for women (RR, 10.3-22.3) and men (RR, 12.5-27.3).
The increase is somewhat of a mystery, the authors said. It can’t be explained by aging, smoking duration, or the improved ability to diagnose COPD. Instead, the finding may be related to changes in the way cigarettes are manufactured.
"For example, the introduction of blended tobacco and genetic selection of tobacco plants lowered the pH of smoke; as a result, inhalation was easier and deeper inhalation was needed for the absorption of protonated nicotine. Other design changes, such as the use of more porous wrapping paper and perforated filters, also diluted the smoke. Deeper inhalation of more dilute smoke increases exposure of the lung parenchyma," they wrote.
Histologic studies have also found a change paralleling these manufacturing differences, the authors noted. The changes "may also have contributed to the shift, beginning in the 1970s, in the histological and topographic features of lung cancers in male smokers, with an increase in the incidence of peripheral adenocarcinomas that largely offset the decrease in squamous-cell and small cell cancers of the central airways. The likely net effect of deeper inhalation on COPD could be wholly detrimental, since COPD results from injury to the lung parenchyma."
Dr. Jha’s study was funded by the Fogarty International Center, the National Institutes of Health, the Canadian Institutes of Health Research, and the Bill and Melinda Gates Foundation. Dr. Thun’s study was funded by the National Institutes of Health and the American Cancer Society. None of the authors of either study had any financial disclosures.