Commentary on Lam <i>et al</i> . 2015: The slow hazards of smoking and the rapid benefits of cessation

From 2000 to 2010, world-wide death rates before age 70 years fell by approximately 19%, driven in large part by reductions in child mortality 1. Death rates from tobacco-related diseases at these ages fall less slowly, partly because previous generations, characterized by fewer people smoking seriously throughout adult life, are being succeeded by generations where many do 2-4. Hence, the proportion of adult deaths due to smoking is set to rise. Indeed, if current smoking patterns persist, tobacco will kill approximately 1 billion people this century, mainly in low- and middle-income countries (LMICs). The details of the evolution of the smoking epidemic in the 21st century have become clearer only in recent years. Large recent studies in the United Kingdom, United States, Japan and India have examined the eventual effects on mortality in populations of men and women where many began to smoke in early adult life and did not quit 5-10. These studies found that in middle age (approximately 30–69 years), cigarette smokers had two or three times the mortality rate of otherwise similar never-smokers, leading to a loss of approximately 10 years of healthy life. This average reduction combines zero loss for those not killed by tobacco with an average loss of substantially greater than a decade for those killed by it. In this issue of Addiction, Lam and colleagues show that elderly Hong Kong residents aged more than 65 years who currently smoke have a mortality rate just lower than twice that for similar never smokers 11. Many of those killed from smoking worldwide are still in middle age (and in India, fully 70% of tobacco deaths occur in middle age [10]), losing many years of good life. Some of those killed in middle age might have died soon in any case, but others might have lived on for decades. On average, those killed in middle age lose approximately 20 years of never-smoker life expectancy. World-wide, approximately 1.3 billion people now smoke, mainly in LMICs where cessation remains uncommon 12. In China, cigarette consumption continues to rise steeply, and now accounts for more than 2 trillion of the global total of approximately 6 trillion cigarettes consumed per year 3. There is a delay of approximately half a century between the widespread adoption of smoking by young adults and the main effect on mortality in later life 2. In US adults, cigarette consumption per adult averaged one, four and 10 per day in 1910, 1930 and 1950. Tobacco caused 12% of all US deaths in middle age in 1950, and this proportion increased to 33% by 1990. A similar pattern was seen approximately 40 years later in Chinese men, who consumed approximately one, four and 10 cigarettes per day in 1952, 1972 and 1992. In 1990, tobacco caused approximately 12% of Chinese male deaths in middle age, and could well cause approximately 33% in 2030 13, 14. Hong Kong men started smoking 2 decades earlier than mainland Chinese men, and among them approximately 33% of all deaths are due to smoking 15. Note that smoking causes few deaths in Chinese women, as fewer than 1% of Chinese women born since 1950 smoke 12. Among men in LMICs, where many smoke but the death rates in middle age from smoking are not yet substantial, a full decade of life expectancy will eventually be lost by young adults who continue to smoke. Tobacco smoking already accounts for between 12 and 25% of adult male mortality in LMICs such as China 13, 14, India 10, Bangladesh 16 and South Africa 17, and on current smoking patterns these hazards are likely to increase. World-wide, approximately half a billion people below age 35 already smoke, and this number is set to increase if current uptake rates persist; at current cessation patterns, relatively few will quit 12. In comparison with the slow increase in tobacco-attributable mortality following the uptake of smoking, the effects of cessation emerge more rapidly 3, 5-10, 18. Those who have smoked cigarettes since early adult life but stop at 30, 40 or 50 years of age regain, respectively, approximately 10, 9 and 6 years of life expectancy, compared with those who continue smoking 5-10. The paper by Lam and colleagues shows that even elderly former smokers reduce their excess risk of all-cause death by approximately 50% compared to current smokers. This might underestimate the hazards of smoking and benefits of cessation: many smokers quit as a result of disease, not to avoid it, and among current smokers some quit between the time of interview and study follow-up. The most important tobacco control strategy is to get current smokers to quit. Substantial increases in excise taxes are the best intervention to raise cessation rates 3, 19, but unfortunately too many governments, most notably China's, are not using substantial increases in excise taxes to curb consumption. None.

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