The impact of tobacco on
health has been extensively documented. This report does not seek to repeat this
information in detail but simply to summarize the evidence. The section is divided into
two parts: first, a brief discussion of nicotine addiction; and second, a description of
the disease bur-den attributable to tobacco.
The addictive nature of tobacco smoking
Tobacco contains nicotine, a substance that is
recognized to be addictive by international medical organizations. Tobacco dependence is
listed in the Inter-national Classification of Diseases. Nicotine fulfills the key
criteria for addiction or dependence, including compulsive use, despite the desire and
repeated attempts to quit; psychoactive effects produced by the action of the substance on
the brain; and behavior motivated by the "reinforcing" effects of the
psycho-active substance. Cigarettes, unlike chewed tobacco, enable nicotine to reach the
brain rapidly, within a few seconds of inhaling smoke, and the smoker can regulate the
dose puff by puff.
Nicotine addiction can be established quickly.
In young adolescents who have recently taken up smoking, saliva concentrations of
cotinine, a breakdown product of nicotine, climb steeply over time toward the levels found
in established smokers (Figure 2.1). The average levels of nicotine inhaled are sufficient
to have a pharmacological effect and to play a role in reinforcing smoking. Yet many young
smokers underestimate their risks of becoming addicted. Between half and three-quarters of
young smokers in the United States say they have tried to quit at least once and failed.
Surveys in the high-income countries suggest that a substantial proportion of smokers as
young as 16 regret their use of cigarettes but feel unable to stop.
It is of course possible to abstain permanently,
as is the case with other addictive substances. However, without cessation interventions,
the individual success rates are low. The most recent research concludes that, of regular
smokers who try to quit unaided, 98 percent will have started again within a year.
Within the next year, tobacco is
expected to kill approximately 4 million people worldwide. Already, it is responsible for
one in 10 adult deaths; by 2030 the figure is expected to be one in six, or 10 million
deaths each year-more than any other cause and more than the projected death tolls from
pneumonia, diarrheal diseases, tuberculosis, and the complications of childbirth for that
year combined. If current trends persist, about 500 million people alive today will
eventually be killed by tobacco, half of them in productive middle age, losing 20 to 25
years of life.
Smoking-related deaths, once largely confined to men in the
high-income countries, are now spreading to women in high-income countries and men
throughout the world (Table 2.1). Whereas in 1990 two out of every three smoking-related
deaths were in either the high-income countries or the former socialist states of Eastern
Europe and Central Asia, by 2030, seven out of every 10 such deaths will be in low- and
middle-income countries. Of the half-billion deaths expected among people alive today,
about 100 million will be in Chinese men.
Long delays between exposure and disease
However, the toll of death and disability from smoking
outside the high-in-come countries has yet to be felt. This is because the diseases caused
by smoking can take several decades to develop. Even when smoking is very common in a
population, the damage to health may not yet be visible. This point can be most clearly
demonstrated by trends in lung cancer in the United States. While the most rapid growth in
cigarette consumption in the United States happened between 1915 and 1950, rates of lung
cancer did not begin to rise steeply until about 1945. Age-standardized rates of the
disease trebled between the 1930s and 1950s, but after 1955 the rates increased much more:
by the 1980s, rates were 11-fold higher than levels in 1940.
In China today, where one-quarter of the world's smokers
live, cigarette consumption is as high as it was in the United States in 1950, when per
capita consumption levels were reaching their peak. At that stage of the U.S. epidemic,
tobacco was responsible for 12 percent of all the nation's deaths in middle age. Forty
years later, when cigarette consumption in the United States was already in decline,
tobacco was responsible for about one-third of the nation's middle-aged deaths. Today, in
a striking echo of the U.S. experience, tobacco is estimated to be responsible for about
12 percent of male middle-aged deaths in China. Researchers expect that within a few
decades, the pro-portion there will rise to about one in three, as it did in the United
States. In contrast, smoking among young Chinese women has not increased markedly in the
past two decades, and most of those women who do smoke are older. Thus, on current smoking
patterns, female tobacco-attributable deaths in China may actually drop from their current
level of about 2 percent of the total to less than 1 percent.
Even in the high-income countries whose populations have been
exposed to smoking for many decades, a clear picture of tobacco-related diseases has taken
at least 40 years to emerge. Researchers calculate the excess risk of death in smokers
through prospective studies that compare the health outcomes of smokers and nonsmokers.
After 20 years of follow-up, in the early 1970s, researchers believed that smokers faced a
one-in-four risk of being killed by tobacco, but now, with more data, they believe that
the risk is one in two.
How smoking kills
In the high-income countries, long-term prospective studies
such as the American Cancer Society's Second Cancer Prevention study, which followed more
than 1 million U.S. adults, have provided reliable evidence of how smoking kills. Smokers
in the United States are 20 times more likely to die of lung cancer in middle age than
nonsmokers and three times more likely to die in middle age of vascular diseases,
including heart attacks, strokes, and other diseases of the arteries or veins. Because
ischemic heart disease is common in high-income countries, the smoker's excess risk
translates into a very large number of deaths, making heart disease the most common
smoking-related cause of death in these countries. Smoking is also the leading cause of
chronic bronchitis and emphysema. It is associated with cancers of various other organs,
including the bladder, kidney, larynx, mouth, pancreas, and stomach.
A person's risk of developing lung cancer is affected more
strongly by the amount of time that they have been a smoker than by the number of
cigarettes they have smoked daily. Put differently, a threefold increase in the duration
of smoking is associated with a 100-fold risk of lung cancer, whereas a threefold increase
in the number of cigarettes smoked each day is associated with only a threefold risk of
lung cancer. Thus those who start to smoke in their teens and who continue face the
For some years, cigarette manufacturers have marketed certain
brands as "low tar" and "low nicotine," a modification that many
smokers believe makes cigarettes safer. However, the difference in the risk of premature
death for smokers of low-tar or low-nicotine brands compared with smokers of ordinary
cigarettes is far less than the difference in risk between nonsmokers and smokers.
The epidemic varies in place as well as in time
Because most long-term studies have been confined to the
high-income countries, data on the health effects of tobacco elsewhere have been scant.
How-ever, recent major studies from China, and emerging studies from India, indicate that
although the overall risks of persistent smoking are about as great as in high-income
countries such as the United States and the United Kingdom, the pattern of smoking-related
diseases in these nations is substantially different. The data from China suggest that
deaths from ischemic heart disease make up a much smaller proportion of the total number
of deaths caused by tobacco than in the West, while respiratory diseases and cancers
account for most of the deaths. Strikingly, a significant minority involve tuberculosis.
Other differences may emerge in other populations; for instance, in South Asia, the
pattern may be affected by a high underlying prevalence of cardiovascular disease. These
results underscore the importance of monitoring the epidemic in all regions. Nevertheless,
despite the different patterns of smoking-related disease in different populations, it
appears that the overall proportion who are eventually killed by persistent cigarette
smoking is generally about one in two in many populations.
Smoking and the health disadvantage
of the poor
As tobacco use is associated with poverty and low
socioeconomic status, so are its damaging effects on health. Analyses for this report show
the impact of smoking on the survival of men in different socioeconomic groups (measured
by income, social class, or educational level) in four countries where the smoking
epidemic is mature-Canada, Poland, the United Kingdom, and the United States.
In Poland in 1996 men with a university education had a 26
percent risk of death in middle age. For men with only primary-level education, the risk
was 52 percent-twice as great. By analyzing the proportion of deaths due to smoking in
each group, researchers estimate that tobacco is responsible for about two-thirds of the
excess risk in the group with only primary-level education. In other words, if smoking
were eliminated, the survival gap between the two groups would narrow sharply. The risk of
death in middle age would fall to 28 percent in men with only primary-level education and
20 percent in those with university education (Figure 2. 2) . Similar results emerge from
the other countries in the study, indicating that tobacco is responsible for more than
half of the difference in adult male mortality between those of highest and lowest
socioeconomic status in these countries. Smoking has also contributed heavily to the
widening of the survival gap over time between affluent and disadvantaged men in these
countries (Figure 2.3).
The risks from others' smoke
Smokers affect not only their own health but the health of
those around them. Women who smoke during pregnancy are more likely to lose the fetus
through spontaneous abortion. Babies born to smoking mothers in high-income countries are
significantly more likely than the babies of nonsmokers to have a low birth weight and up
to 35 percent more likely to die in infancy. They also face higher risks of respiratory
disease. Recent research has shown that a carcinogen found only in tobacco smoke is
present in the urine of newborn babies born to smokers.
Cigarette smoking accounts for much of the health
disadvantage of babies born to poorer women. Among white women in the United States,
smoking alone has been found to be responsible for 63 percent of the difference in birth
weight between babies born to college-educated women and babies born to those who received
a high school education or less.
Adults exposed chronically to others' tobacco smoke also face
small but real risks of lung cancer and higher risks of cardiovascular disease, while the
children of smokers suffer a range of health problems and functional limitations.
Nonsmokers who are exposed to smoke include the children and
the spouses of smokers, mostly within their own homes. Also, a substantial number of
nonsmokers work with smokers, or in smoky environments, where their expo-sure over time is
The earlier a smoker starts, the greater the risk of
disabling illnesses. In high-income countries with long-term data, researchers have
concluded that smokers who start early and smoke regularly are much more likely to develop
lung cancer than smokers who quit while they are still young. In the United Kingdom, male
doctors who stop smoking before the age of 35 survive about as well as those who never
smoked. Those who quit between the ages of 35 and 44 also gain substantial benefits, and
there are benefits at older ages, too.
In sum, then, the epidemic of smoking-related disease is
expanding from its original focus in men in high-income countries to affect women in
high-income countries and men in low- and middle-income countries. Smoking is increasingly
associated with social disadvantage, as measured by income and educational levels. Most
new smokers underestimate the risk of becoming addicted to nicotine; by early adulthood,
many regret starting to smoke and feel unable to stop. Half of long-term smokers will
eventually be killed by tobacco, and half of these will die in middle age.