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Smoking kills 3 out of 4 smokers?–A 10-year follow-up study in Hong Kong, China


World Health Organization states “Tobacco kills up to one in every two users”. This absolute risk of 1/2 was based on a relative risk (RR) of 2 and the attributable fraction (AF) in the exposed of 50% ((RR-1)/RR)) for total mortality due to smoking. Recent large UK and US cohort studies have shown an RR of 3, meaning 2 out of 3 smokers will be killed by smoking. RRs could be under-estimated partly because few studies examined oldest old smokers separately. We examined RR and AF of total mortality due to smoking in the older (65-84y) and oldest old (85+y) people in Hong Kong, China.


Multivariable Cox regression was used to assess the risks of total mortality from smoking using a population-based prospective cohort of 65,510 Chinese aged 65+ years enrolled from 1998 to 2001 and followed until May 2012.


For participants aged 65-84 years, after adjustment for sex, age, education, social security assistance, housing type, monthly expenditure, alcohol use and health status, the RR was 1.93 (95% confidence interval (CI) 1.84-2.03), corresponding to an AF of about 50%. For 85+ years, the adjusted RR was 1.29 (1.05-1.58), corresponding to an AF of about 25%. Therefore for every 12 smokers who start smoking at young age, 4 will be killed by smoking at middle age, 4 at old age, leaving 1/4 oldest old surviving smokers to die from smoking later.


Our study has shown that smoking kills one out of four oldest old smokers, and together with existing evidence, we conclude that the total mortality risk due to smoking starting at young age is greater than 1/2, should be at least 2/3, and could be up to 3/4. Global disease burden estimates due to smoking based on an RR of 2 may need to be revised upwards.

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