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No Safe Level of Smoking: Mortality Risks Described for Occasional Smokers and Smokers Who Cut Back

Posted on November 26, 2018

Computer-illustrated pack of cigarettes with red circle and slash

Tobacco products are estimated to cause seven million deaths per year worldwide, including 480,000 deaths from cigarette smoking alone. Even though smoking rates have declined over the last few decades, about 15% of US adults currently smoke and 39% smoked regularly at some point in their life. Additionally, an estimated 189 million adults, worldwide, smoke tobacco “occasionally” but not every day. However, few studies have examined how non-daily smoking and changes in the number of cigarettes smoked per day over the lifetime affect mortality. DCEG investigators conducted two studies to begin addressing this gap in knowledge.

In a study published in American Journal of Preventive Medicine on October 24, 2018, investigators reported that lifelong non-daily cigarette smokers who had never smoked daily were 1.7 times more likely to die from any cause during the follow-up period than never smokers. Additionally, relative to never smokers, lifelong non-daily smokers lived five years less and daily smokers lived ten years less. The data came from the 1991, 1992, and 1995 U.S. National Health Interview Surveys (NHIS), a nationally representative sample of 70,913 U.S. adults (aged 18–95 years), as well as additional supplements that collected more detailed information on smoking habits.

A second study published in American Journal of Epidemiology on October 9, 2018, examined the impact of changes in the number of cigarettes smoked per day (CPD) on risk of all-cause and cause-specific mortality. The authors noted a dose-response with changes in CPD: risk of death during the follow-up period was lowest among never smokers and progressively increased among former smokers, those who reduced their CPD but did not quit, those who maintained a consistent CPD, and those who increased their CPD from ages 25-29 to 50-59. Notably, relative to never smokers, participants who only decreased their CPD but did not quit were more than twice as likely to die from any cause. The data came from over 250,000 participants in the NIH-AARP Diet and Health Study.

These results may also have implications for risk prediction. Currently, eligibility for lung cancer screening is typically determined based on life-time pack-years of exposure, the product of smoking duration, and typical or recent CPD. These studies demonstrate that lung cancer mortality risk varies substantially with changes in CPD over the lifetime. Models that incorporate CPD at just a single time in life may not optimally identify people who should be screened for lung cancer.

References:

Inoue-Choi M., et al. Non-Daily Cigarette Smokers: Mortality Risks in the U.S. Am J Prev Med. 2018 Oct 24. [Epub ahead of print] DOI: 10.1016/j.amepre.2018.06.025.

Inoue-Choi M., et al. Reductions in Cigarettes per Day and Mortality Among Older Adults in The United States. Am J Epidemiol. 2018 Oct 9. [Epub ahead of print] DOI: 10.1093/aje/kwy227