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Original Investigation
January 2017

Association of Long-term, Low-Intensity Smoking With All-Cause and Cause-Specific Mortality in the National Institutes of Health–AARP Diet and Health Study

Author Affiliations
  • 1Division of Cancer Epidemiology & Genetics, National Cancer Institute, National Institutes of Health, Rockville, Maryland
  • 2Office of Science, Center for Tobacco Products, US Food and Drug Administration, Silver Spring, Maryland
JAMA Intern Med. 2017;177(1):87-95. doi:10.1001/jamainternmed.2016.7511
Key Points

Question  Do people who smoke at low-intensity (ie, <1 or 1-10 cigarettes per day) over their lifetime have increased risk of mortality relative to those who never smoke?

Findings  Among 290 215 older adults of the National Institutes of Health–AARP Diet and Health Study cohort, low-intensity smoking over the lifetime was associated with a significantly higher risk of all-cause mortality, including deaths from lung cancer and cardiovascular disease. Former smokers who had consistently used fewer than 1 or 1 to 10 cigarettes per day but who had quit smoking had progressively lower risks with a younger age at cessation.

Meaning  This study provides evidence that individuals with lifelong, low-intensity smoking have higher mortality risks than those who never smoked and would benefit from cessation.

Abstract

Importance  A growing proportion of US smokers now smoke fewer than 10 cigarettes per day (CPD), and that proportion will likely rise in the future. The health effects of smoking only a few CPD over one’s lifetime are less understood than are the effects of heavier smoking, although many smokers believe that their level is modest.

Objective  To evaluate the associations of long-term smoking of fewer than 1 or 1 to 10 CPD (low intensity) with all-cause and cause-specific mortality compared with never smoking cigarettes.

Design, Setting, and Participants  Prospective cohort study of 290 215 adults in the National Institutes of Health–AARP (formerly known as the American Association of Retired Persons) Diet and Health Study who were aged 59 to 82 years in calendar years 2004-2005 (baseline). Data were gathered with a questionnaire assessing lifetime cigarette smoking history. Hazard ratios (HRs) and 95% CIs were determined for all-cause mortality and cause-specific mortality through the end of 2011. Hazard ratios and 95% CIs were estimated using Cox proportional hazards regression models using age as the underlying time metric and adjusted for sex, race/ethnicity, educational level, physical activity, and alcohol intake. Data analysis was conducted from December 15, 2015, to September 30, 2016.

Exposures  Current and historical smoking intensity during 9 previous age periods (from <15 years to ≥70 years) over the lifetime assessed on the 2004-2005 questionnaire.

Main Outcomes and Measures  All-cause and cause-specific mortality among current, former, and never smokers.

Results  Of the 290 215 cohort participants who completed the 2004-2005 questionnaire, 168 140 were men (57.9%); the mean (SD) age was 71 (5.3) years (range, 59-82 years). Most people who smoked fewer than 1 or 1 to 10 CPD at baseline reported smoking substantially higher numbers of CPD earlier in their lives. Nevertheless, 159 (9.1%) and 1493 (22.5%) of these individuals reported consistently smoking fewer than 1 or 1 to 10 CPD in each age period that they smoked, respectively. Relative to never smokers, consistent smokers of fewer than 1 CPD (HR, 1.64; 95% CI, 1.07-2.51) and 1 to 10 CPD (HR, 1.87; 95% CI, 1.64-2.13) had a higher all-cause mortality risk. Associations were similar in women and men for all-cause mortality and were observed across a range of smoking-related causes of death, with an especially strong association with lung cancer (HR, 9.12; 95% CI, 2.92-28.47, and HR, 11.61; 95% CI, 8.25-16.35 for <1 and 1-10 CPD, respectively). Former smokers who had consistently smoked fewer than 1 or 1 to 10 CPD had progressively lower risks with younger age at cessation. For example, the HRs for consistent smokers of fewer than 1 and 1 to 10 CPD who quit at 50 years or older were 1.44 (95% CI, 1.12-1.85) and 1.42 (95% CI, 1.27-1.59), respectively.

Conclusions and Relevance  This study provides evidence that individuals who smoke fewer than 1 or 1 to 10 CPD over their lifetime have higher mortality risks than never smokers and would benefit from cessation. These results provide further evidence that there is no risk-free level of exposure to tobacco smoke.

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