Socioeconomic status (SES) is strongly associated with smoking behaviour.1,2,3,4
Not only are social inequalities in smoking prevalence pervasive, but they have been widening in such countries as Australia, the UK, the USA, Spain, Italy and Denmark in the past few decades.1,5,6,7,8,9,10,11
Social class differences in smoking contribute substantially to social inequalities in mortality.1
Unless action is taken to address the high prevalence of smoking among lower SES groups, we can expect a future widening of social inequalities in health. Any such action requires knowledge of the pathways from SES to smoking behaviour. This study examines SES variations in knowledge of the health effects of smoking and thereby sheds light on the mechanism of the SES–smoking relationship.
Many theories of behaviour change rely on a person's risk awareness and access to information.12,13,14
Knowledge of the health effects of smoking is one of the possible prerequisites for quitting and is targeted by prevention programmes.12
In a study of 9500 employed men in the USA, Nourjah and colleagues reported that knowledge of smoking as a risk factor for heart disease was a significant predictor of being an ever‐smoker, intention to quit, and having quit smoking.15
Risk perception is shaped by such factors as warning labels on and availability of tobacco products, health education in media, and pattern of use by celebrities.16
An Australian study revealed that health warnings (including information on carbon monoxide in cigarette smoke) on cigarette packs were associated with increased knowledge of the constituents of cigarette smoke and a reduction in cigarette consumption.17
In developed countries, the majority of people are aware of the association of smoking with heart disease and lung cancer.18
Awareness of the association of smoking and other conditions such as stroke and impotence (which directly affects only men) is less and rarely reported.
Less is known about smokers' knowledge of the constituents of tobacco smoke. Cigarette smoke contains numerous toxic chemicals such as carbon monoxide, cyanide and arsenic. Carbon monoxide is a major contributor to cardiovascular disease from smoking. It impairs oxygen transportation in the blood, thereby reducing the amount of oxygenated blood circulated to body organs and tissues. It is also strongly linked with the development of coronary heart disease.19
Cyanide released from a cigarette can be 160 times more than the level considered safe. It has a direct, harmful effect on the cilia, a part of the natural lung clearance mechanism in humans, thereby increasing the likelihood of developing disease.19
The risk indices of cyanide and arsenic, related to the cardiovascular system, are significant with just one cigarette per day.20
The few reports that assess smokers' awareness of these toxins in smoke suggest a very low level of awareness.21,22
The association between SES and knowledge of some of the health effects of smoking has been reported in the past. Nourjah and colleagues found that, in the USA, white‐collar employees were more likely to be knowledgeable of the effect of smoking on heart disease.15
Ayanian used a sample of 737 smokers in the USA and reported that high education was related to a greater awareness that smoking increased the risk of myocardial infarction.23
Similar findings about the association of education and occupation with the knowledge of heart disease are reported in Canada12
The few studies that have examined the association of SES with knowledge of lung cancer25,26
suggest a positive relationship. There are no published studies on knowledge that smoking is a cause of impotence. Neither do we know of any studies on SES variations in knowledge of chemical constituents of smoke.
Given that having knowledge of the health effects of smoking is essential for behaviour change, an examination of socioeconomic differences in knowledge can help explain part of the pronounced SES differentials in smoking prevalence and cessation rates. The aim of this study was to use population data from the USA, UK, Canada and Australia, and investigate socioeconomic and country variations in smokers' knowledge that smoking causes heart disease, stroke, impotence and lung cancer, and that smoke contains cyanide, mercury, arsenic and carbon monoxide. We also examined SES and country variations in whether smokers thought nicotine causes most of the cancer. Nicotine is the addictive drug in cigarette smoke but there is no evidence that it causes cancer. Knowledge of this is important because nicotine replacement therapies are a proven effective therapy for smoking cessation, and if smokers believe nicotine causes cancer they are unlikely to want to use these treatments.