I just came on two important papers — 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 and Association between long-term low-intensity cigarette smoking and incidence of smoking-related cancer in the National Institutes of Health-AARP cohort by Maki Inoue Choi and her colleagues at the National Cancer Institute and FDA — that show that even a little smoking is dangerous. They used the NIH-AARP Diet and Health Study to assess the dose-response between smoking and a wide range of diseases over a lifetime.
While they found a dose-response, i.e., heavier smoking is worse than lighter smoking, the risk did not decrease proportionally. For example, people who consistently smoked less than 1 cigarette per day over their lifetime had about 44% the risk of death as very heavy smokers who smoked 21-30 cigarettes per day (hazard ratio 1.64; 95% CI 1.07-2.51 for <1 CPD vs 3.73; 3.23-4.31 for 21-30 CPD).
The specific risks varied by disease. Smoking <1 CPD carried about 22% of the lung cancer risks as smoking 21-30 CPD whereas for cardiovascular disease the risks were almost the same.
Quitting smoking at any age was associated with lower risks among light smokers (see figure above, which is from their JAMA Internal Medicine paper).
These results are also consistent with a meta-analysis conducted by FDA that found that simply reducing cigarettes per day was not associated with a significant reduction in all-cause mortality.
What are the implications for harm reduction?
In the face of evidence that e-cigarettes as consumer products do not help smokers stop smoking, e-cigarette advocates have claimed that e-cigarettes help smokers cut down. While the evidence for this claim is mixed, the fact that even a little smoking still carries substantial risks means that any benefits of cutting down are likely to be less than a proportionate reduction in risk, even ignoring the risks e-cigarette use carries. Including the e-cigarette risk likely leads to an overall increase in risk even if cigarette consumption drops.
And, of course, quitting smoking (and e-cigarettes) entirely is always a good idea.
Here are the full citations and abstracts for the two papers:
Inoue-Choi M, Liao LM, Reyes-Guzman C, Hartge P, Caporaso N, Freedman ND. 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. JAMA Intern Med. 2017 Jan 1;177(1):87-95. doi: 10.1001/jamainternmed.2016.7511. PMID: 27918784; PMCID: PMC5555224. It is available here.
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.
Inoue-Choi M, Hartge P, Liao LM, Caporaso N, Freedman ND. Association between long-term low-intensity cigarette smoking and incidence of smoking-related cancer in the national institutes of health-AARP cohort. Int J Cancer. 2018 Jan 15;142(2):271-280. doi: 10.1002/ijc.31059. Epub 2017 Oct 10. PMID: 28929489; PMCID: PMC5748934. It is available here.
An increasing proportion of US smokers smoke ≤10 cigarettes per day (CPD) or do not smoke every day, yet the health effects of low-intensity smoking are poorly understood. We identified lifelong smokers of <1 or 1-10 CPD and evaluated risk of incident cancer among 238,525 cancer-free adults, aged 59-82, in the NIH-AARP Diet and Health Study. A questionnaire administered in 2004-2005 assessed CPD during nine age-periods (<15 to ≥70). We estimated hazard ratios (HR) and 95% confidence intervals (CI) using multivariable-adjusted Cox proportional hazards regression with age as the underlying time metric. Of the 18,233 current smokers, (7.6%), 137 and 1,243 reported consistently smoking <1 CPD and 1-10 CPD, respectively. Relative to never smokers, current smokers who reported consistently smoking 1-10 CPD over their lifetime were 2.34 (95% CI = 1.86-2.93) times more likely to develop smoking-related cancer. Current lifetime smokers of <1 CPD were 1.89 (95% CI = 0.90-3.96) times more likely to develop tobacco-related cancer, although the association did not reach statistical significance. Associations were observed for lifelong smoking of ≤10 CPD with lung cancer (HR = 9.65, 95% CI = 6.93-13.43); bladder cancer (HR = 2.22, 95% CI = 1.22-4.05); and pancreatic cancer (HR = 2.03, 95%CI: 1.05-3.95). Among lifelong ≤10 CPD smokers, former smokers had lower risks of smoking-related cancer with longer time since cessation and longer smoking duration. Lifelong <1 and 1-10 CPD smokers are at increased risk of incident cancer relative to never smokers and would benefit from cessation, providing further evidence that even low-levels of cigarette smoking cause cancer.