BMJ Open. 2026 Aug 4;16(8):e107667. doi: 10.1136/bmjopen-2025-107667.
ABSTRACT
OBJECTIVES: To assess levels of and trends in knowledge that smoking and secondhand smoke (SHS) cause lung cancer and cardiovascular disease (CVD) in 46 countries over two decades.
DESIGN: Longitudinal cohort and repeat cross-sectional surveys.
SETTING: Nationally representative surveys in 26 International Tobacco Control (ITC) Project countries (2002-2022) and 32 Global Adult Tobacco Survey (GATS) countries (2008-2020).
PARTICIPANTS: Adults (aged 18+ years) who smoke tobacco (26 ITC countries: n=133 410; 32 GATS countries: n=110 537).
ANALYSIS OUTCOMES: Current use of cigarettes at least monthly (all ITC countries) and/or bidis at least monthly (ITC India, Bangladesh and Zambia) and current use of any combustible tobacco products (all GATS countries). We conducted individual-level analyses of the ITC and GATS data separately, without combining the datasets or analysing previously published summary statistics. Generalised estimating equations and weighted multinomial regression models assessed country-level prevalence of knowledge for three smoking and two SHS outcomes. Multilevel models estimated mean prevalence across all countries and tested within-country linear trends over time for five disease indicators by survey. Across 12 countries with data from both surveys, correlations between ITC and GATS assessed consistency across indicators.
RESULTS: Knowledge that smoking causes lung cancer was highest (ITC=92.2%, GATS=91.9%), followed by heart disease (ITC=84.7%)/heart attack (GATS=80.0%) and stroke (ITC=75.0%, GATS=66.1%). Knowledge that SHS causes lung cancer (ITC=77.3%, GATS=82.1%) was highest, followed by heart attack (ITC=61.8%)/heart disease (GATS=72.5%) (all p<0.0001). In ITC and GATS countries, the average change in knowledge across the five diseases was +0.14% per year. There was agreement between the ITC and GATS data (range: Pearson correlations=0.60-0.81 across the five indicators).
CONCLUSIONS: There is a need to improve and sustain people's knowledge of diseases caused by smoking and SHS, especially CVD risks.
PMID:42552006 | DOI:10.1136/bmjopen-2025-107667