Tobacco smoking is projected to cause one billion deaths worldwide this century. Two-thirds of adult men in China smoke.
In a study from Oxford Population Health and elsewhere, scientists found smoking increases the risks of 56 diseases and kills more than one million adults in China each year from 22 different causes.
They found that around half of those who start smoking cigarettes as young men (before the age of 18) will eventually be killed by tobacco, unless they give up permanently.
Smoking also increases the risks of developing a wide range of conditions that do not generally cause deaths, such as asthma, peptic ulcer, cataract, diabetes, and other metabolic diseases.
The adverse effects of smoking have been known for many years, but very few studies, even those in high-income Western countries, have systematically assessed the impact of smoking on an extensive range of diseases within the same population.
In the study, the researchers used data from the China Kadoorie Biobank to comprehensively assess the health effects of tobacco smoking on death and hospitalization from a range of diseases and to examine the benefit of smoking cessation.
The team tested 512,000 adults who were recruited during 2004–08 from 10 diverse urban and rural areas across China.
Of all of the participants, 32.4% had ever smoked regularly; this was much higher in men (~74%) than in women (~3%).
Participants were followed for a median of 11 years, during which more than 48,800 participants died and around 1.14 million new disease events occurred.
The team found among almost 85 causes of death and 480 diseases studied, smoking was linked to higher risks of 22 causes of death (17 for men and nine for women) and 56 diseases (50 for men and 24 for women).
Compared with people who had never smoked, men who had ever smoked regularly had about 10% higher risk of developing any disease, ranging from 6% higher risk to 216% for larynx cancer.
They also experienced much more frequent and longer stays in hospital, particularly due to cancers and respiratory diseases.
People who stopped smoking voluntarily (ie before developing major diseases) were found to have similar levels of risk of developing the disease as people who had never smoked, about 10 years after quitting.
Despite the lower smoking prevalence and intensity in female smokers, they had comparable relative risks of major respiratory diseases, demonstrating a special vulnerability to the harm of tobacco (compared to men).
The results are a stark reminder of the serious consequences of smoking and the benefits of stopping before any major illness develops.
Although some associations were weaker than those seen in high-income populations, these are likely to be explained by the more recent widespread uptake of smoking in China.
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The study was conducted by Ka Hung Chan et al and published in The Lancet Public Health.
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