Philippe Tellier, MD
Chronic smoking remains a major cause of premature mortality on a global scale. Despite intensified efforts to combat this scourge, a quarter of deaths among middle-aged adults in Europe and North America are attributed to it. However, over the past decades, antismoking campaigns have borne fruit, and many smokers have quit before the age of 40 years, enabling some case-control studies.
Among those abstainers who made the right choice, the excess mortality attributable to smoking over a lifetime would be reduced by 90% compared with controls who continued smoking. The estimated benefit is clear, but the analysis lacks nuance. Is smoking cessation beneficial even at older ages? If so, is the effect measurable in terms of magnitude and speed of the effect? An article published online on February 8, 2024, in The New England Journal of Medicine Evidence provided some answers to these questions.
Four-Cohort Meta-Analysis
The study was a meta-analysis of individual data collected within four national cohort studies that were linked to each country’s death registry. Two of these studies were nationally representative. The National Health Interview Survey involved a sample of US citizens living in the community, aged 20-79 years, who were included annually in the cohort between 1997 and 2018. The second, the Canadian Community Health Survey, included subjects in the same age group, with samples analyzed between 2000 and 2014.
In Norway, three cohort studies conducted between 1974 and 2003, in which participants aged 25-79 years were included, were combined to form the Norwegian Health Screening Survey. These were the Counties Study (1974-1988), the 40 Years Study (1985-1999), and the Cohort of Norway (1994-2003), respectively. The fourth cohort was established through recruitment via the UK Biobank, with adults aged 40-73 years invited to participate in the survey. The data analysis ultimately covered a relatively heterogeneous total population of 1.48 million adults, all from high-income countries and followed for 15 years. It relied on the Cox proportional hazards model applied to each study, considering smoker vs nonsmoker status, as well as the time elapsed since smoking cessation (less than 3 years, between 3 and 9 years, or at least 10 years). Statistical adjustments made in the context of multivariate Cox analysis considered age, education, alcohol consumption, and obesity.
Excess Mortality Confirmed
At the end of follow-up, 122,697 deaths were recorded. The comparison of smokers and nonsmokers confirmed smoking-related excess mortality, with adjusted hazard ratios (HRs) estimated at 2.80 for women and 2.70 for men. Smoking shortened life expectancy in the 40- to 79-year-age group by 12 years for women and 13 years for men, in terms of overall mortality. In terms of smoking-attributable specific mortality, the corresponding figures reached 24 and 26 years, respectively. Respiratory diseases ranked highest in both sexes (HR, 7.6 for women and 6.3 for men), followed by cardiovascular diseases (HR, 3.1 for women and 2.9 for men) and cancers (HR, 2.8 for women and 3.1 for men).
The Earlier, the Better
Smoking cessation halves overall excess mortality. Above all, quitting before age 40 years brings overall mortality back to the level of nonsmokers as early as the third year after quitting. The excess mortality decreases even more as the cessation period is prolonged, even after age 40 years. Thus, cessation ≥ 10 years in smokers aged 40-49 years almost cancels out overall excess mortality (−99% in women, −96% in men). The trend is almost as favorable in the older age group (50-59 years), with corresponding figures of −95% and −92%, respectively.
Long-term survival increases in the early years after cessation, especially if it occurs at a younger age, but the benefit remains tangible even in older smokers. Thus, cessation of less than 3 years, effective in patients aged 50-59 years, reduces overall excess mortality by 63% in women and 54% in men. In patients aged 60-79 years, the figures are −40% and −33%, respectively.
Naturally, the earlier the cessation, the greater the number of years gained. It is 12 years for cessation before age 40 years, reduced to 6 years for cessation between 40 and 49 years, and 2.5 years when it is even later (50-59 years). These quantitative results are approximate, given the methodology (a meta-analysis) and some heterogeneity in the studies, as well as the multitude of potential confounding factors that have not all been considered. Nevertheless, the results probably contain a kernel of truth, and their optimistic implications should be highlighted to encourage smokers to abstain, even older ones. Better late than never, even if the benefit of cessation is maximal when it occurs as early as possible, knowing that a minimum of three years of cessation would be sufficient to gain years of life.
This story was translated from JIM, which is part of the Medscape professional network, using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.
Leave a Reply