Results from a large pooled cohort study in the USA show that even smoking less than 10 cigarettes a day significantly increases the risk of dying from lung cancer or respiratory disease.1
In the USA, the proportion of people who smoke is 14%. This is the lowest level ever. Within the smoking population, however, the proportion of light users has increased from 16% to 27%. It is therefore important to look at the risk of death from respiratory diseases and lung cancer in this group, who probably think that the risk is lower if they smoked less.
The pooled NHLBI cohort study adjusted the data of 4 US cohorts with information on the general population. 18,730 participants with a uniform smoking status participated in the study. The smokers were divided into light/social smokers (<10 CPD), smokers (10-20 CPD), and heavy smokers (>20 CPD) according to their amount of cigarettes per day (CPD). To calculate their risks, a proportional Cox risk regression was carried out, adjusted for potential confounding factors such as gender, age, ethnic background, education, and weight.
The respiratory mortality outcome was classified using ICD-9 and 10 for different lung diseases such as asthma, emphysema, COPD, chronic bronchitis, and respiratory insufficiency. Lung cancer mortality was also defined using ICD-9 and 10. Participants were followed up median over a period of 17 years. They had an average age of 63 years, 69% were Caucasian and 56% female, 2% were light smokers and 8% were heavy smokers.
The incidence density was 20 calculated cases per 10,000 person-years for respiratory mortality and 17 for lung cancer mortality. Light smoking led to 2.5 times higher risk of respiratory mortality and almost 9 times higher probability of dying from lung cancer compared to non-smoking (hazard ratio 8.6). Light smoking also increased the risk of respiratory mortality and lung cancer mortality. Compared to the risk of heavy smokers, it was as high as 49% and 71% respectively.
"In summary, our results suggest that low-intensity smoking is disproportionately harmful. The best way to reduce the risk of dying from respiratory disease or lung cancer is to stop smoking completely," said Dr. Pallavi Balte (Columbia University, New York).
1. Balte P, et al Association of low-intensity smoking with respiratory and lung cancer mortality. E-Poster no.4389. ERS International Virtual Congress 2020, 7-9 September, 2020.