Looking through the smoke screen: reviewing the risks of occasional smoking

This editorial refers to ‘Occasional smoking is a risk factor for myocardial infarction in the population–based Tromsø Study, 2001–21’, by S. Tiwari et al., https://doi.org/10.1093/eurjpc/zwaf182. Over the last decade, the prevalence of daily smoking has decreased, while occasional smoking has become increasingly common.1 Occasional cigarette smoking is heterogeneously defined, including light or low volume smoking, non-daily, intermittent smoking, or chipping. Its current prevalence in Europe shows a wide variation depending on the country, from 6% to 28% of smokers.2 The shift from daily to occasional smoking could be partly due to global tobacco control policies, denormalization of smoking in public, and the rise of alternative nicotine products like vaping or pouches. The article by Tiwari et al.3 in this edition of the Journal, sheds new light on the cardiovascular risks of occasional smoking. Occasional smokers usually show specific characteristics when compared with daily smokers. They are usually younger and have a higher level of education.2 As such, they are a heterogenous group, with variability in the number and frequency of cigarettes used, as well as their likelihood of transitioning to either quitting or progression to daily smoking.4 Subsequently, the long-term health effects of occasional smoking remain poorly delineated, and it is crucial to better understand the risks these individuals face. The Tromsø study is a Norwegian prospective cohort study running from 1974 to 2016. Seven Rounds of survey have been conducted providing a rich prospective repository of data on >45 000 subjects. The current study involved 15 617 participants from the Tromsø 5 (2001) and Tromsø 6 (2007–8) cohorts. Occasional smoking was defined as ‘sometimes’ in Tromsø 5 and further clarified as ‘sometimes but not daily’ in Tromsø 6. Ascertainment of myocardial infarction (MI) was performed through linkage to national registries, with a reported high degree of accuracy. The mean follow-up duration was for 11 years and the end of follow-up period was determined at 31 December 2021. Consistent with global trends, the authors found an increase in the prevalence of occasional smoking from 6.2% to 9.7% between 2001 and 2007–8. Occasional smokers had a higher education level, and a lower prevalence of hypertension compared with daily smokers. There were 1297 participants who experienced an MI during the follow-up period. Participants who were never smokers had the lowest incidence of MI (33.6 per 10 000 person years) and daily smokers had the highest incidence (64.6 per 10 000 person years). Compared to never smokers, occasional smokers had a 41% (HR 1.41) higher age- and sex-adjusted risk of MI even after adjusting for multiple confounding variables. Occasional smokers also had a higher age- and sex-adjusted risk when compared with former smokers (HR 1.35) suggesting an improvement in CV risk with quitting. Interestingly, sex-specific analysis showed that women who were occasional smokers experienced twice the risk as never smokers (HR 2.08), whereas men experienced only an 11% increase in risk (HR 1.11). This sex difference while not statistically significant, is consistent with the increased smoking-related risk seen in women in other studies.5 The strength of this study is the large prospective cohort with a high participation rate and a long duration of follow-up. The study suffers from limitations of self-reported data, potential selection bias due to the voluntary nature of survey and is limited in the granularity available on the nature of cigarette use beyond pack years. While prior data from the Tromsø study show an association between overall smoking and total mortality, other CV risks of occasional smoking are not as well defined.6 Table 1 presents a synopsis of major studies exploring this risk, among which an increased hazard associated with occasional smoking in women is mostly described. The current study highlights these risks and confirms a dose response relationship between smoking and CV risk, with the lowest risk being in non-smokers and the highest in daily smokers, the risk in occasional smokers being between these two extremes. This is especially important to highlight as educated occasional smokers tend to underestimate their own risk, self-categorize as ‘non-smokers’ and have a greater belief in their agency to quit anytime they choose.11 These smokers may be more motived to quit when educated upon the dangers of occasional smoking. There is also a need to develop novel strategies to help these smokers. For example, both the 5As smoking cessation tool and cessation pharmacotherapy are known to be effective in daily smokers, but the applicability to occasional smokers remains to be studied. Studies of cardiovascular risks associated with occasional smoking Studies of cardiovascular risks associated with occasional smoking This study is unique in its addition to the expanding body of research on the dangers of occasional smoking, particularly in women. It reinforces that there is no safe level of smoking and underscores the importance of identifying the heterogeneity in this group when developing policy and tobacco cessation initiatives.