A large international study has found that millions of smokers still do not fully understand how tobacco damages the cardiovascular system, despite more than two decades of warnings, smoke-free policies and global public-health campaigns. Researchers from the University of Waterloo and the Global Tobacco Control Program at the U.S. Centers for Disease Control and Prevention analyzed information from more than 240,000 adult smokers in 46 countries. Their findings suggest that public knowledge of tobacco’s most dangerous effects remains sharply uneven: lung cancer is widely recognized, but the links between smoking, heart attack, stroke and second-hand smoke are far less understood.
The study offers a striking picture of what smokers know—and what they do not. More than 90 percent of participants understood that smoking can cause lung cancer. However, only about 80 percent identified heart disease or heart attack as a consequence of smoking, while roughly 70 percent knew that smoking can cause stroke. These gaps are medically significant because cardiovascular disease accounts for a substantial proportion of tobacco-related deaths. Smoking is not simply an irritant that harms the lungs; it is a systemic exposure that alters blood vessels, promotes clot formation and accelerates the biological processes underlying heart attacks and strokes.
Tobacco smoke contains thousands of chemicals, including nicotine, carbon monoxide, fine particulate matter and numerous oxidizing compounds. Nicotine stimulates the sympathetic nervous system, increasing heart rate and blood pressure while contributing to dependence. Carbon monoxide binds to haemoglobin more readily than oxygen does, reducing the blood’s oxygen-carrying capacity. Other components injure the endothelium, the thin layer of cells lining blood vessels. Once this protective surface is damaged, inflammation and the accumulation of fatty plaques become more likely. Smoking also makes platelets more prone to clump together, increasing the chance that a disrupted plaque will produce a life-threatening clot.
These mechanisms help explain why tobacco exposure can trigger an acute cardiovascular event even in people who do not consider themselves heavy smokers. A heart attack generally occurs when blood flow through a coronary artery becomes severely restricted or blocked, while an ischemic stroke occurs when a clot prevents oxygen from reaching part of the brain. Smoking can contribute to both conditions by narrowing arteries, destabilizing arterial plaques and increasing coagulation. The danger is compounded when smoking is combined with other risk factors such as high blood pressure, diabetes, elevated cholesterol, obesity or physical inactivity. Yet the researchers found that these cardiovascular pathways have not become nearly as familiar to the public as the connection between cigarettes and lung cancer.
Awareness of second-hand smoke was even more troubling. In several high-income countries—including Australia, Germany, England, the United States, New Zealand and Canada—fewer than half of adult smokers knew that breathing other people’s tobacco smoke can cause heart disease or heart attack. China, home to approximately 300 million smokers, was among the countries where awareness was lowest. Second-hand smoke contains a complex mixture of sidestream smoke released from a burning cigarette and exhaled mainstream smoke. Even relatively brief exposure can impair vascular function, increase platelet activation and produce measurable changes in blood pressure and arterial stiffness, meaning that cardiovascular harm does not require years of active smoking.
The researchers examined trends across two decades and found little overall progress in knowledge about the health risks of smoking and second-hand smoke. Some countries, including Bangladesh, India, Thailand and Vietnam, recorded increased awareness of cardiovascular harms. In contrast, knowledge about the cardiovascular effects of second-hand smoke declined in most of the high-income countries included in the analysis, among them Canada, the United States, New Zealand, England and Japan. The result is particularly unexpected because many of these countries have implemented extensive tobacco-control programs. The findings suggest that progress in legislation does not automatically guarantee progress in public understanding, especially when health messages become less visible or fail to emphasize risks beyond lung disease.
Knowledge of second-hand smoke’s relationship to lung cancer also remained lower than knowledge about active smoking, with little improvement over time. This distinction matters because people who do not smoke may still be exposed at home, in vehicles, workplaces or other environments where tobacco smoke accumulates. Children, pregnant people, older adults and individuals with existing heart or lung conditions can be especially vulnerable. Although smoke-free laws reduce exposure in public settings, household exposure remains difficult to address without clear communication about its consequences. A message focused only on smell, discomfort or respiratory irritation may not convey that second-hand smoke can also affect the circulation and heart.
Dr. Janet Chung-Hall, a research scientist with the International Tobacco Control Policy Evaluation Project at Waterloo and lead author of the study, described the knowledge gaps as deeply concerning. She emphasized that smoking causes more than two million cardiovascular deaths worldwide each year, making the lack of awareness a major public-health problem rather than a minor communications failure. Dr. Geoffrey T. Fong, principal investigator of the ITC Project and a University Professor of Psychology and Public Health Sciences at Waterloo, said that knowledge is an important first step toward quitting and protecting others from second-hand smoke. Understanding risk does not guarantee behavior change, but it can strengthen motivation, increase receptiveness to cessation support and make tobacco-control policies more effective.
The researchers point to large pictorial health warnings and sustained mass-media campaigns as tools that could close the gap. Graphic warnings can communicate biological damage quickly, even when people do not read detailed text, while repeated campaigns can reinforce information that might otherwise fade from memory. Effective messaging would need to place cardiovascular disease alongside lung cancer, clearly explaining that smoking can cause heart attack and stroke and that second-hand smoke can harm the heart as well. The findings also support the broader implementation of measures contained in the World Health Organization Framework Convention on Tobacco Control, a global treaty with more than 180 signatory countries. As tobacco companies continue to market nicotine products across diverse populations, the study suggests that public education must remain persistent, scientifically precise and impossible to ignore.
Subject of Research: People
Article Title: Smokers still largely unaware of heart disease risks
News Publication Date: 4-Aug-2026
Web References: https://bmjopen.bmj.com/content/16/8/e107667
References: BMJ Open, DOI: 10.1136/bmjopen-2025-107667
Keywords: tobacco smoking, second-hand smoke, cardiovascular disease, heart attack, stroke, lung cancer, public health, tobacco control, health awareness, smoking cessation
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