• Overview
• Definition
• Incidence, prevalence and trends
• Risk factors
• Health consequences
• Costs
• Contributors

Risk Factors

We have divided these into risk factors for taking up smoking (which occurs mainly in adolescence) and risk factors for stopping smoking (which occurs mainly in adulthood).

Risk factors for smoking in adolescence

There are many risk factors for smoking in adolescence. These are summarised in two systematic reviews. ^{1 2} In general, most attention has focused on the social environment.

Friendships

The observational evidence is clear that the more smokers there are in the social environment, the higher the chance that a young person will become a smoker. ^{1 2} However, interventions (even intensive interventions) that have tried to change this have generally not shown any long term benefits in reducing the uptake of smoking. ³ Others have emphasised that young people select their friends because they are like minded and this explains some or all of the association between having friends that smoke and becoming a smoker. ^{4 5 6 7 8} It is an active area of research.

Educational involvement

Any variable that measures success at school, liking school, or thinking school is useful is strongly associated with a decreased likelihood of smoking. ^{1 9} There is also some evidence that school characteristics may influence the likelihood that young people will smoke. ^{10 11 12}

Social class

There is a much weaker relationship between social class and regular (weekly) smoking in adolescence than in adulthood. However, if we define a smoker as smoking at least daily the social class gradient is stronger. If we define a smoker as smoking as several cigarettes per day it is stronger still. ¹³

Smokers from poorer backgrounds start smoking at an earlier age than do smokers from wealthier backgrounds. ¹⁴ A study following young people from early adolescence to early adulthood showed that, although there was little relation between current (parental) social class and smoking in adolescence, smoking in adolescence predicted the social class of destination of the young person. ^{15 16} This is probably due to the association between educational engagement and smoking. ^{1 9}

Risk factors for smoking in adults

The risk factors for smoking in adulthood are related to the factors that cause adolescents and young adults to start smoking and the factors that help or hinder cessation. In a strict epidemiological sense, these risk factors are not helpful explanatory risk factors, but they do carry an important public health message.

Lopez described four phases of the tobacco epidemic. ¹⁷ The UK is in the fourth phase, where smoking becomes increasingly concentrated in the most disadvantaged sectors of society. Almost every marker of social disadvantage and socioeconomic status is associated with smoking. In the 1960s, there was little association between smoking and disadvantage. It is becoming increasingly strong and this will continue unless we take specific public health actions.

Socioeconomic status

Even among a group of poor people, those who are very poor are more likely to smoke. In one study, 80% of poor people with all the risk factors listed in Box 1 smoked compared with 20% people who had none of these risk factors. ¹⁸ People who can least afford to smoke are most likely to do so, and many smokers go without food and other basics to smoke. ¹⁸

Poorer smokers are more responsive than richer ones to tobacco tax rises. ¹⁹ Most smokers do not stop in response to tax rises, so they are retrogressive (although helpful to people who do give up).

Mental illness

Smoking is strongly associated with mental illness. There are three possible reasons ²⁰ :

• The illness and smoking have a set of common or associated risk factors, such as growing up in poverty
• The illness causes people to smoke. This may be a form of self medication, such as in attention deficit hyperactivity disorder where the stimulant nicotine might reduce symptoms of the condition. It may also be as a reaction to medications (such as to antipsychotic drugs in schizophrenia) that reduce dopamine in the reward system and which might be counteracted by nicotine
• Smoking may cause mental illness. Smokers believe that smoking helps them deal with stress, but studies show that most people are less stressed once they stop smoking.

Most people with severe mental illness smoke and smoke more heavily than healthy peers. Rates of death from cardiovascular disease are much higher in people with mental illness than expected, so stopping smoking is an important part of care. ²⁰

Risk factors for stopping smoking

We know surprisingly little about what makes people attempt to stop smoking.

Risk factors for wanting to, intending to, and attempting to stop smoking

Some studies report that social class is a risk factor for attempting to stop smoking. ²¹ UK data, however, show no association between social class and wanting to stop. There is a weak association between lower social class and intention to stop, and no association between social class and having tried to stop. ^{14 22 23} One study reported that people who attempted to stop smoking believed more strongly that smoking was bad for their health and that their partner wanted them to stop, and rated smoking as giving them less enjoyment. ²³ All these associations were weak.

Risk factors for successful cessation

Unsurprisingly, and not very informatively, there is a strong association between wanting to and intending to stop smoking and actually attempting it. ²⁴ However, recent evidence suggests that even people who do not intend to stop smoking do attempt it. ²⁵ Offering treatment to people who do not intend to stop in the future may therefore be helpful.

Because nearly all attempts to stop smoking fail, the risk factors for success are different from the risk factors for attempting to stop. The same study that found that social class did not predict attempts to stop smoking showed that lower social class predicted that those attempts would be more likely to fail. ²³ Even people of lower social class attending stop smoking services are about 50% more likely to fail than their more affluent neighbours. ²⁶ However, most factors associated with success were related to nicotine dependence: the more dependent a person is on nicotine, the lower the likelihood of a successful quit attempt. ²³ Because nicotine dependence and social class are associated, part of the reason for the higher failure rate in people from lower social classes may be due to nicotine dependence.

It is a truism in behavioural research that past behaviour predicts future behaviour. Consistent evidence shows that the longer a person has abstained for in previous attempts, the greater the probability of achieving long term success. ²⁷ However, the predictive accuracy of these risk factors is poor, so we cannot use them to guide treatment.

Risk factors for cessation in pregnancy

Stopping smoking in pregnancy is strongly associated with socioeconomic position. More than 60% of managerial and professional class smokers stop during pregnancy, while more than 60% of routine and manual groups continue to smoke. ¹⁴