Smoking kills at least 1 out of 2 smokers?--A 10-year follow-up study in Hong Kong, China

INTRODUCTION:  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.

METHODS:  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.

RESULTS:  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%.

CONCLUSIONS:  Our study has shown that smoking kills one out of two older smokers and one out of four oldest old smokers in Hong Kong which is at an earlier stage of epidemic (by about 20 years) than the West. Global disease burden estimates due to smoking based on an RR of 2 may need to be revised upwards.