Changes in knowledge of the major harms of tobacco smoking and secondhand smoke exposure among adults who smoke: findings from 26 countries of the International Tobacco Control (ITC) Project (2002-2022) and 32 countries of the Global Adult Tobacco Survey (GATS) (2008-2020).

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.