Association between duration or intensity of tobacco smoking and olfactory function: A cross-sectional study among smokers willing to quit smoking

Introduction: A range of studies suggests that people who smoke tobacco have impaired olfactory function, but few have explored the association between smoking history, such as duration or intensity, and olfactory function. We aimed to determine the prevalence of olfactory dysfunction among adult smokers and to test the association between duration or intensity of smoking and olfactory function. Methods: For this cross-sectional study we consecutively invited adult smokers, participating in a smoking cessation trial conducted in five Swiss study sites, to undergo olfactory function testing at baseline from September 2020 to June 2021. We tested olfactory function with the Burghart's Sniffin' Sticks 16-item identification test resulting in an olfactory identification score (OIS) of 0-16 points. We defined olfactory dysfunction as an OIS ≤11 points. We fitted multivariable regression models to test the association between the OIS or olfactory dysfunction and self-reported smoking parameters [cigarettes per day (CPD), years of smoking (YOS) and pack-years] adjusted for relevant confounders such as demographics, substance use and comorbidities. Results: Of 388 eligible participants, 375 (96.7%) completed the olfactory testing. Mean age was 39.0 years (SD=13.2), and 44.8% identified as women. The participants smoked on average 15 (SD=7.1) cigarettes per day for a median duration of 18 years (IQR: 11-28). Mean OIS was 13.3 (SD=1.8) and 12.0% had olfactory dysfunction. Olfactory dysfunction was significantly associated with pack-years (OR=1.03; 95% CI: 1.00-1.05) but not with YOS or CPD. OIS was negatively associated with pack-years (coefficient= -11.11; 95% CI: -4.29 - -17.94). OIS was not significantly associated with YOS or CPD. Conclusions: Among smokers smoking ≥5 cigarettes per day participating in a smoking cessation trial, about one in ten had olfactory dysfunction. Higher number of pack-years were associated with a worse measure of olfactory function and with olfactory dysfunction. Clinical trial registration: This sub-study of the ESTxENDS trial is pre-registered on the official website of ClinicalTrials.gov. Identifier: NCT04617444.