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

Health Consequences

The risks of smoking

Tobacco smoking is the biggest risk factor for premature morbidity and mortality in the UK. It is responsible for half of the deaths of all those who continue to smoke, and a half of these deaths occur before retirement age. ¹

• The relative risk for all cause mortality for men who smoke has been estimated at 2.3 and at 2.19 from two different studies. ^{2 3} For women who smoke the relative risk is 1.8. ² This means that people who smoke are about twice as likely to die at any given age.
• The size of the risk varies with the level of consumption, from 1.79 among people who smoke one to 15 cigarettes per day to 2.61 among people who smoke 25 or more cigarettes per day. ³
• People who continue to smoke lose 10 years of life. ³

Smoking kills people in the UK primarily by inducing cardiovascular disease (coronary heart disease and stroke), some cancers, and respiratory disease (primarily chronic obstructive pulmonary disease). An exhaustive list of the diseases that are associated with smoking and thought to be caused by it, along with an appraisal of the evidence linking the exposure (smoking) to the outcome (the disease), is presented in the Surgeon General’s report. ⁴ An estimate of the size of the risk and the relation to consumption levels is presented in British Doctors Study, which was the first study to show that smoking caused lung cancer. ³

Coronary heart disease

In the British Doctors Study smokers were 45% more likely to die from coronary heart disease than were non-smokers. The relative risk of developing coronary heart disease from smoking is 1.45. Other data indicate that the relative risk of developing ischaemic heart disease from smoking is higher than this: overall between 2.0 and 3.0, but that the relative risk is much higher for premature heart disease than for heart disease in old age. ²

One study found that the relative risk (95% confidence intervals) of death arising from smoking one to four cigarettes per day was 2.65 (2.02–3.48), whereas from the relative risk from smoking 10–14 cigarettes per day was 3.24 (2.81–3.74). ⁵ For cardiovascular disease the number of cigarettes smokes has little affect; smoking more cigarettes is not much worse than smoking fewer. The corollary of this, however, is that even for light smokers smoking is an important risk factor for heart disease. Given the high likelihood of disease and death from heart disease, even light smokers face substantial risks to their health.

Cancer

Smokers are 14 times more likely than non-smokers to die from lung cancer, which is the most common form of cancer caused by smoking. The relative risk of lung cancer is 14. However, coronary heart disease is seven times more common than lung cancer. This means that smoking causes more deaths from heart disease (3.1/1000/year) than from lung cancer (2.3/1000/year). The population attributable risk is higher.

In general, for most cancers there is a strong dose–response relation. This means that people who have smoked for longer and who smoke the most are at markedly greater risk of developing cancer than those who smoke fewer cigarettes of for not as long. The relative risk (95% confidence interval) for developing lung cancer from smoking one to four cigarettes per day was 2.84 (0.96–8.45) but the relative risk from smoking 10–14 cigarettes per day was 17.98 (10.92–29.61).

The number of deaths from cancer is shown in Figure 1, with cancers caused by smoking marked by a black arrow. Smoking is a more important risk factor for some cancers than others, and more detail on the size of the risk faced by smokers and former smokers can be found on the American Cancer Society website. ⁶

Chronic obstructive pulmonary disease

Around 13% of current smokers older than 35 and 40% of current smokers older than 65 have chronic obstructive pulmonary disease, much of it undiagnosed. ⁸ It is usually progressive, disabling in some, and can lead to an unpleasant death.

The benefits of stopping smoking

The benefits of stopping smoking are considerable, even after many years. The best data come from the British Doctors Study. ³ This study found that if people stopped smoking between age 25 and 34 their mortality rate was the same as that of people who had never smoked.

For every decade people smoke for after age 40, they lose three years of life. In other words, each year of smoking after age 40 loses a smoker 3.6 months, which emphasises the imperative to give up soon.

Cardiovascular disease

The benefits of stopping smoking vary by disease. In coronary heart disease the benefits occur soon after stopping. A study in middle aged women (where the relative risk from smoking is high) found that smokers were 4.23 times more likely to develop ischaemic heart disease than were people who had never smoked, while for former smokers the relative risk was 1.48. ⁹ One third of the excess risk from smoking was eliminated within two years of stopping (the relative risk dropped to about 3.0) and the risk then declined over 10–14 years to that of people who had never smoked.

It is possible to undo all the damage to coronary arteries if smokers stop smoking. Stopping confers a benefit even in people who already have ischaemic heart disease. The relative risk (95% confidence intervals) of ischaemic heart disease is 0.68 (0.57–0.82), and this benefit is apparent within two years of stopping. ¹⁰

Cancer

For cancers, particularly those strongly related to smoking such as lung cancer, former smokers face substantially raised risks of getting cancer even 20 or more years after stopping. These risks, however, are also substantially lower than for continuing smokers. ¹

Chronic obstructive pulmonary disease

Progression of chronic obstructive pulmonary disease is measured by the reduction in forced expiratory volume in one second (FEV1). (This is how much air can be exhaled in one second). FEV1 peaks at age 25 and declines with age. On average, smokers’ lung function declines faster than that of non-smokers. But after stopping smoking lung function improves slightly in the first year and subsequently the rate of decline of lung function returns to that of non-smokers. ¹¹ Smokers with impaired lung function or early chronic obstructive pulmonary disease can therefore substantially reduce their chance of developing severe respiratory disability by stopping smoking.

The benefits of reducing smoking

Given the clear dose–response relation between cigarette consumption and disease, it is reasonable to assume that reducing smoking would reduce the risk of disease also. However, there is evidence that this is not the case. In a 30 year follow up of Norwegian smokers, people who smoked 15 or more cigarettes at baseline and then reduced consumption by at least 50% were compared with people who continued smoking 15 or more cigarettes per day. The relative risks (95% confidence intervals) of people who reduced their consumption compared with those who did not were 1.02 (0.84–1.22) for all cause mortality, 1.02 (0.75–1.39) for cardiovascular disease, 0.96 (0.45–1.41) for ischaemic heart disease, 0.86 (0.57–1.29) for smoking related cancer, and 0.66 (0.36–1.21) for lung cancer. ¹²

This means that reducing consumption of cigarettes has minimal benefit. People who become used to a certain level of nicotine consumption consciously or unconsciously regulate their intake to achieve this. Reducing the number of cigarettes smoked per day usually leads to compensatory increases in nicotine intake (and therefore the tars that carry the nicotine into the lungs). This effect might explain these seemingly contrary findings.

The risks of smoking and benefits of stopping smoking in pregnancy

Smoking is the most important modifiable risk factor for poor outcome in pregnancy. There is some, but not conclusive, evidence that the risk of miscarriage is increased with smoking. Smoking increases the risk of placenta praevia and placental abruption, but lowers the incidence of pre-eclampsia. Smoking causes preterm delivery and fetal growth restriction. ⁴

Stopping smoking reduces the incidence of preterm delivery and intrauterine growth restriction and interventions to help women stop have shown clear evidence of these benefits. ¹³

Sperm quality is reduced in men who smoke.