Knowing the risks
Over the years, epidemiological studies have associated smoking with many different serious and fatal diseases.
The diseases most studied have been lung cancer, chronic obstructive pulmonary disease and coronary heart disease, mainly because these are all important causes of death in many countries.
These statistical studies consistently report very strong associations between smoking and lung cancer, such that it is reasonable to conclude that smoking is an important cause of lung cancer. The statistics report higher incidence of lung cancer in groups that smoke for more years and smoke more cigarettes per day, with the length of time people have been smoking thought to be the most important factor. It has been estimated (though estimates vary considerably) that around 10-15 per cent of lifelong smokers get lung cancer and, that of all the people who get lung cancer, around 90 per cent are smokers. After quitting, risks begin to decline and will vary according to a person’s smoking history. A former smoker’s level of risk may approach that of a non-smoker after about 10 years or so of abstinence.
COPD includes chronic bronchitis and emphysema. The statistical studies consistently report strong relationships between smoking and COPD that are of similar magnitude to the risks identified between smoking and lung cancer. As with lung cancer, the incidence is highest in groups that smoke for longer and smoke more cigarettes per day. Quitting is thought to slow the progression of the disease. Risks in groups of ex-smokers tend to remain higher than for non-smokers, but lower than for those who continue to smoke.
Smoking is one of the causes of coronary heart disease. Heart disease is linked with many factors along with smoking; health authorities also regard high cholesterol, high blood pressure, obesity and lack of exercise as important. Some studies have reported that the risks for heart disease are greater in groups of people that have more than one of these risk factors (for example, smokers who take little exercise). The smoking-related risks of heart disease reduce relatively rapidly after quitting.
Public health authorities advise that pregnant women should not smoke, and have publicised this widely. Many statistical studies have reported a link between lower birth weight in babies and mothers who smoke throughout pregnancy. Some statistical studies have reported, amongst other factors, links between smoking in pregnancy and infant mortality, premature birth, miscarriage and stillbirth.
Epidemiological studies have reported various increased risks of other diseases among smokers. These include stroke (cerebrovascular disease), heart attack, aortic aneurysm, diseases affecting the circulation (such as peripheral vascular disease) and cancers of the throat, mouth, bladder, stomach and kidneys. The strength of the evidence linking these illnesses with smoking varies amongst the diseases and amongst different groups of people in different countries.