In a recent study published in the EClinicalMedicine, a group of researchers assessed how tobacco use and exposure influence stroke risk, varying by type, region, and income level.

Background

Tobacco use significantly contributes to global mortality, disability, and cardiovascular diseases, with 29.6% of men and 5.3% of women worldwide being daily smokers. In 2016, stroke was responsible for 5.5 million deaths and 116.4 million disability-adjusted life years (DALYs), accounting for 11.5% of global deaths. Although global smoking rates are declining, some regions report increases among both genders.

Smoking is a top risk factor for stroke, especially ischemic strokes, with the INTERSTROKE study showing a 12.4% global stroke risk from smoking. Exposure to secondhand smoke also increases stroke risk, though quitting smoking can quickly reduce this risk. Further research is essential to develop targeted interventions and policies that address the impacts of tobacco use and exposure on stroke risk across diverse populations and regions.

About the study 

The INTERSTROKE study, conducted internationally, embarked on identifying stroke risk factors by enlisting participants from 142 centers across 32 countries from January 11, 2007, to August 8, 2015. The study spanned various regions, including Western Europe, North America, Eastern Europe, the Middle East, Africa, South Asia, China, Southeast Asia, and South America, and classified countries based on income levels into high, upper-middle, and low-middle/low income. It focused on individuals experiencing their first acute stroke, confirmed through neuroimaging, compared to community or hospital-based controls, with all participants providing informed consent.

Data collection involved a structured questionnaire and physical examinations to ascertain tobacco use habits, including cigarettes, non-cigarette smoked and smokeless tobacco, and environmental tobacco smoke (ETS) exposure, alongside physiological measurements and health history. Tobacco use was categorized into current, former, and never, with additional details on the type and frequency of usage. The study precisely recorded ETS exposure based on interactions with smokers in the participant’s environment.

Statistical analysis employed univariate associations for preliminary data exploration, with more complex multivariable logistic regression models adjusting for potential confounders like age, sex, and lifestyle factors to assess the impact of tobacco on stroke risk. The population attributable risk (PAR) was calculated to estimate the impact of tobacco use on stroke incidence, adjusted for confounders, and stratified by various subgroups. Analyses utilized advanced statistical software, ensuring a comprehensive understanding of the relationship between tobacco exposure and stroke risk.

Study results 

In the present study, researchers presented baseline characteristics of both controls and cases, focusing on various stroke subtypes and the impact of different tobacco products, including age, body mass index (BMI), and cholesterol levels, among others. The data revealed gaps in several areas, such as psychosocial factors and diabetes history, though the majority of participants had recorded data for lipids and Hemoglobin A1c (HbA1c) levels.

The prevalence of smoking, detailed by region, sex, and quantity of tobacco products used daily, highlighted significant regional variations. For instance, Eastern Europe and North America showed a higher prevalence of smoking among young females, while the highest rates among young males were observed in China. 

The findings indicated that current smoking was linked to an increased risk across all stroke types, with the risk being particularly pronounced for ischemic stroke and less so for intracerebral hemorrhage (ICH). Among ischemic stroke etiological subtypes, current smokers showed varied odds ratios (ORs), with large vessel stroke presenting the highest risk.

Filtered cigarettes, non-filtered cigarettes, and beedies (alone or in combination) were all associated with increased stroke risk. Notably, the risk of ischemic stroke escalated with the number of cigarettes smoked per day, showing a dose-response relationship, but former smoking did not significantly impact stroke risk.

The study further revealed that the risk and PAR of stroke associated with current smoking varied significantly by region, with Western Europe/North America exhibiting the highest risk and PAR, especially among young smokers. Income levels also influenced the odds ratio and PAR, decreasing from high-income countries to low-middle/income countries. A notable dose-response relationship between the number of cigarettes smoked per day and stroke risk was evident across income levels, particularly in high-income countries.

Exposure to ETS was reported by a significant portion of controls, with increased exposure hours correlating with higher odds of ischemic stroke, ICH, and various Trial of Org 10172 (TOAST) subtypes. Extended weekly exposure to ETS heightened the risk for all stroke types, underlining the detrimental effects of both active smoking and secondhand smoke exposure on stroke risk.