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Social smoking: Do not underestimate the risks

Presented by
Dr Pallavi Balte, Columbia University, USA
ERS 2020
The risk of smoking even less than 10 cigarettes a day should not be underestimated as it still entails a substantial risk of lung cancer or respiratory diseases as cause of death [1].

The proportion of people in the USA who smoke has decreased from 20.9% in 2005 to 13.7% in 2018 [2]. Yet, within the smoking population, the rate of so-called light smokers has risen from 16% to 27% [3]. A good reason to look at the risk of mortality of respiratory disease and lung cancer in these smokers, who probably think that their smoking entails a low risk.

Dr Pallavi Balte (Columbia University, USA) presented results from the NHLBI pooled cohort study [1]. Dr Balte and colleagues harmonised data from 4 cohorts with information on the general population including 18,730 participants with consistent smoking status. Smokers were classified according to their number of cigarettes per day (CPD) into light/social smoker (<10 CPD), smokers (10-20 CPD), and heavy smokers (>20 CPD). To calculate their risks, a Cox proportional hazard regression was fit that adjusted for potential confounders like sex, age, race, education, and weight. The outcome of respiratory mortality was classified using the International Classification of Diseases (ICD)-9 and IC-10 codifications for several diseases, including asthma, emphysema, COPD, chronic bronchitis, and respiratory failure. Likewise, lung cancer mortality was also defined by ICD-9 and ICD-10 codes. Participants were followed up for a median of 17 years. They had a mean age of 63 years, 69% were Caucasian, 56% were female, and 2% were light and 8% were heavy smokers.

The incidence density rate was calculated in cases per 10,000 person-years with 20 for respiratory mortality and 17 for lung cancer mortality. Light smoking lead to a risk of respiratory mortality that was 2.5 times greater than the risk for non-smokers and had a nearly 9 times higher likelihood of lung cancer mortality (HR 8.6). Interestingly, light smoking was also associated with a risk for respiratory mortality and lung cancer mortality that was as high as 49% and 71% of the risk of heavy smokers.

“In conclusion, our findings suggest that low-intensity smoking is disproportionately harmful and in order to reduce the risk of dying from respiratory disease or lung cancer the best action is to quit smoking completely,” was the bottom line according to Dr Balte.


    1. Balte P, et al. Association of low-intensity smoking with respiratory and lung cancer mortality. Abstract 4389, ERS International Virtual Congress 2020, 7-9 Sept.
    2. Centres for Disease Control and Prevention. Retrieved from: https://www.cdc.gov/tobacco/data_statistics/fact_sheets/adult_data/cig_smoking/index.htm [Accessed on 30 September 2020].
    3. Hackshaw A, et al. BMJ. 2018;360:j5855.


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