Cigarette smoking history, e-cigarette use, and Long COVID: a population-based analysis

Long COVID imposes a substantial public health burden following the SARS-CoV-2 pandemic, yet the contribution of electronic cigarette (e-cigarette) use, alone or alongside cigarette smoking, remains inadequately characterized in population-representative data. We conducted a cross-sectional analysis of 9274 adults aged 16 years and older from the pooled 2023-2024 Scottish Health Survey, a nationally representative household survey. Cigarette smoking and e-cigarette use were classified into seven mutually exclusive categories, and the outcome was survey-defined self-reported Long COVID, based on symptoms persisting for more than four weeks after first having COVID-19. Survey-weighted logistic regression was used to estimate crude and adjusted odds ratios, with adjustment for survey year, age group, sex, area deprivation, ethnicity, alcohol use, and educational attainment. Overall, 7.4% of adults reported Long COVID. Compared with never cigarette/e-cigarette users, adjusted odds were higher among former cigarette smokers currently using neither product (adjusted odds ratio 1.40, 95% confidence interval 1.12-1.76) and among former smokers currently using e-cigarettes exclusively (1.56, 1.09-2.24). No statistically detectable associations were observed among former e-cigarette users who had never smoked, current e-cigarette users who had never smoked, exclusive current cigarette smokers, or dual users. The two elevated associations persisted after additional adjustment for asthma, chronic obstructive pulmonary disease, diabetes, and cardiovascular disease. The observed pattern may reflect previous cigarette exposure, health-related smoking cessation or switching, reverse causation, and residual selection or confounding; the cross-sectional design does not permit an independent contribution of e-cigarette use to be determined.