Smoking lowers life expectancy in Japan by 10 years

Smoking cuts life expectancy by ten years in Japan, researchers report in a paper published by the BMJ on bmj.com on Oct. 25, 2012.

by Bruce Sylvester – taken from the British Medical Journal (BMJ) – The investigators in Oxford (UK) and Japan evaluated the impact of smoking on mortality in a large group of Japanese people living in Hiroshima or Nagasaki in 1950.

The Life Span Study (LSS) was initiated in 1950 to study effects of radiation in over 100,000 subjects. Most had experienced minimal radiation exposure, and the data could therefore be used to study other risk factors. The LSS researchers got smoking information for 68,000 men and women,  with an average of 23 years follow-up on these subjects.

As background the investigators noted that older generations did not usually begin smoking until  adulthood, and usually smoked only a few cigarettes per day. However, Japanese subjects in the study born from 1920-45 usually started to smoke in early adult life, like Western counterparts.

The differences in smoking commencement age is reflected in the mortality patterns. Smokers born before 1920 lost just a few years. Men born between 1920-45 who started  smoking before age 20 lost nearly a decade of life expectancy. Results for women who had smoked before age 20 were similar, though the total number of female smokers was much smaller.

The investigators found that smokers who stopped smoking before age 35 avoided almost all the excess risk among continuing smokers, and those who stopped by age 40 avoided most of the risk.