- Category: Other Health News
- Published on Tuesday, 29 January 2013 00:00
- Written by Liz Highleyman
Smoking can knock a decade off life expectancy relative to people who never smoked, and smoking-related mortality rates are now nearly equal for men and women, according to 2 studies published in the January 24, 2013, New England Journal of Medicine. But quitting by age 40 cuts the risk by 90%, and even later is still beneficial.
It is well known that smoking is a major cause of morbidity and mortality, contributing to a range of conditions including cancer, cardiovascular disease, and chronic obstructive pulmonary disease (COPD). Men have long had high smoking-related mortality; smoking among women became socially acceptable later, but they have now caught up.
Analysis of 7 Cohorts
As described in the first study, Michael Thun from the American Cancer Society and colleagues looked at trends in mortality across 3 time periods -- 1959-1965, 1982-1988, and 2000-2010 -- comparing absolute and relative risk of death according to sex and self-reported smoking habits.
The analysis included more than 1 million people in 2 historical U.S. cohort studies (Cancer Prevention Studies I and II, which began enrollment in 1965 and 1982, respectively) and more than 900,000 participants in 5 pooled contemporary U.S. cohort studies, all of whom reached the age of 55 years during follow-up.
Most were white and they had a higher level of education than the general population, with many of the contemporary cohort participants being healthcare workers. More than half of the contemporary current smokers reported smoking fewer than 20 cigarettes per day in 2000, but about 25% had smoked for at least 50 years.
- In the contemporary cohorts the proportion of current smokers decreased over time, to 9.3% among men and 9.7% among women.
- Among participants who had never smoked, all-cause mortality decreased by about half between 1959-1965 and the contemporary period.
- Women smokers, in contrast, saw no decrease in all-cause mortality, while men who smoked saw a decrease of only about one-quarter.
- Risk of death from all causes among current smokers increased across all time periods, with a relative risk (RR) of 2.80 for men and 2.76 for women compared with never-smokers.
- Among men age 55-74 and women age 60-74 who were current smokers in the contemporary period, the rate of death from all causes combined was at least 3 times higher compared with those who never smoked.
- Women who currently smoked had relative risks of death from lung cancer of 2.73 in the 1960s, 12.65 in the 1980s, and 25.66 in the contemporary studies relative to those who had never smoked.
- For men, the corresponding relative risks were 12.22, 23.81, and 24.97, respectively, indicating that men and women have similar risk in the contemporary era.
- Men and women smokers in the contemporary cohorts also had similar relative risks for death due to other causes:
o COPD: RR 25.61 for men and 22.35 for women;
o Ischemic heart disease: 2.50 and 2.86, respectively;
o Stroke: 1.92 and 2.10, respectively;
o All causes combined: 2.80 and 2.76, respectively.
- Relative risks of death due to lung cancer, COPD, and all causes rose with increases in the number of cigarettes smoked per day and the number of years of smoking.
- Mortality due to COPD among men who smoked continued to rise in the contemporary cohorts in nearly all age groups and for all categories of duration and intensity of smoking.
- Former smokers who stopped smoking at earlier ages had progressively lower risk of death due to lung cancer and COPD compared with those who continued to smoke in the contemporary period.
- People who quit smoking by age 40 "avoided nearly all the excess smoking-related deaths" from these conditions.
- People who quit before age 60 had lower relative risk than those who did not quit, even if they smoked fewer than 10 cigarettes per day.
"The risk of death from cigarette smoking continues to increase among women and the increased risks are now nearly identical for men and women, as compared with persons who have never smoked," the study authors concluded.
"Convergence of the relative risks for men and women results from the convergence of smoking patterns among men and women since the 1960s," they explained in their discussion, confirming the maxim that "women who smoke like men die like men."
On the bright side, "Our analyses of data from former smokers confirm that quitting smoking at any age dramatically lowers mortality from all major smoking-related diseases," they wrote. "[N]early all the excess risk can be avoided if a person quits smoking before 40 years of age."
National Health Interview Survey Analysis
In a related study described in the same issue, Prabhat Jha from the Center for Global Health Research in Toronto and coworkers looked at smoking and its relation to mortality in a large, prospective, nationally representative study, estimating the benefits of smoking cessation at various ages.
This analysis included data from 113,752 women and 88,496 men age 25 or older who participated in the U.S. National Health Interview Survey between 1997 and 2004. Mortality among survey participants was assessed by matching their records to the National Death Index. NIHS excludes prisoners, active-duty military personnel, and patients in long-term care facilities. Black and Hispanic populations are oversampled, but data are then weighted to match national racial/ethnic proportions.
Most smokers had started before age 20. Current smokers had lower education levels, lower body-mass index, and were more likely to drink alcohol than non-smokers. The proportion of participants who quit smoking rose with age, but women were less likely to quit than men.
- Among participants age 25-79, the all-cause death rate for current smokers was about 3 times higher than the rate for participants who had never smoked (hazard ratio 2.8 for men and 3.0 for women).
- Most excess mortality among smokers was due to cancer, cardiovascular, respiratory, and other diseases that can be caused by smoking, accounting for 60% of deaths.
- The probability of surviving from 25 to 79 years of age was about twice as great among those who had never smoked compared with current smokers (70% vs 38% for women; 61% vs 26% for men).
- Life expectancy decreased by more than 10 years among current smokers compared with those who never smoked.
- Adults who quit smoking at age 25-34 gained about 10 years, those who quit at age 35-44 gained 9 years, and those who quit at age 45-54 gained 6 years relative to those who continued smoking.
Based on these findings, the researchers wrote, "Smokers lose at least one decade of life expectancy, as compared with those who have never smoked. Cessation before the age of 40 years reduces the risk of death associated with continued smoking by about 90%."
"The women in this cohort represent the first generation of women in the United States in which those who smoked began early in life and smoked for decades, and the risks of death for these women are about 50% greater than the risks reported in the 1980s studies, they explained.
"Cessation at around 40 years of age results in approximately a 90% reduction in the excess risk of death associated with continued smoking in later middle age and old age," they wrote. "That is not to say, however, that it is safe to smoke until 40 years of age and then stop, for the remaining excess risk of about 20%... is substantial; it means that about 1 in 6 of these former smokers who dies before the age of 80 years would not have died if their death rates had been similar to those for persons who had never smoked who were similar in educational levels, adiposity, and alcohol use."
In an accompanying editorial, Steven Schroeder from the University of California at San Francisco noted that smoking prevalence in Thun's analysis was only 9.5% -- about half the prevalence found in a 2011 survey -- likely because the cohort studies overrepresented people who were better educated (a demographic that smokes less). The NHIS survey omitted groups known to have higher-than-average smoking rates, including incarcerated people.
"[B]ecause smokers in these populations smoke more cigarettes per day, the findings probably underestimate the overall mortality among smokers," he suggested.
Schroedersummarized the 2 important messages that emerge from these articles. "First, in terms of health benefits, it is never too late to quit," he wrote. "Second, the importance of smoking as a health hazard needs to be elevated. More women die of lung cancer than of breast cancer. But there is no 'race for the cure' for lung cancer."
"Because smoking has become a stigmatized behavior concentrated among persons of low social status," he continued, "it risks becoming invisible to those who set health policies and research priorities."
P Jha, C Ramasundarahettige, V Landsman, et al. 21st-Century Hazards of Smoking and Benefits of Cessation in the United States. New England Journal of Medicine 368(4):341-350. January 24, 2013.
M Thun, B Carter, D Feskanich, et al. 50-Year Trends in Smoking-Related Mortality in the United States. New England Journal of Medicine 368(4):351-364. January 24, 2013.
S Schroeder. New Evidence That Cigarette Smoking Remains the Most Important Health Hazard. New England Journal of Medicine 368(4):389-390. January 24, 2013.
L Shepherd, St. Michael's Hospital. Smokers Who Quit Before Age 40 Have Lifespan Almost as Long as People Who Never Smoked. Press release. January 23, 2013.