タバコ1本で寿命が11分縮む。

このエントリーをはてなブックマークに追加

2010年12月03日(Fri) 13:54

タバコの健康障害をわかりやすく説明する方法として、
喫煙者の平均寿命の短縮から、1本あたり何分短縮されるかを計算し、
「タバコ1本で寿命が○分縮む」と表現されることがあります。

その一例をご紹介しておきます。

=============================

BMJ. 2000 January 1; 320(7226): 53.
   
PMCID: PMC1117323

Time for a smoke? One cigarette reduces your life by 11 minutes

Mary Shaw, Economic and Social Research Council research fellow
Richard Mitchell, research fellow Danny Dorling, reader
School of Geographical Sciences, University of Bristol, Bristol BS8 1SS

Editor—Studies investigating the impact on mortality of socioeconomic
and lifestyle factors such as smoking tend to report death rates, death
rate ratios, odds ratios, or the chances of smokers reaching different
ages. These findings may also be converted into differences in life expectancy.
We estimated how much life is lost in smoking one cigarette.

Our calculation is for men only and based on the difference in life expectancy
between male smokers and non-smokers and an estimate of the total number of
cigarettes a regular male smoker might consume in his lifetime. We derived the
difference in life expectancy for smokers and non-smokers by using mortality
ratios from the study of Doll et al of 34 000 male doctors over 40 years.1

The relative death rates of smokers compared with non-smokers were threefold for
men aged 45-64 and twofold for those aged 65-84,1 as corroborated elsewhere.2

Average life expectancy from birth for the whole population or subgroups can
be derived from life tables. Applying the rates of Doll et al to the latest interim
life tables for men in England and Wales, with adjustment for the proportion of
smokers and non-smokers in each five year age group,3 

we found a difference in life expectancy between smokers and non-smokers of 6.5 years.
We used the proportion of smokers by age group, the median age of starting smoking,
and the average number of cigarettes smoked per week in the 1996 general household
survey.4

We calculated that if a man smokes the average number of cigarettes a year (5772)
from the median starting age of 17 until his death at the age of 71 he will
consume a total of 311 688 cigarettes in his lifetime.

If we then assume that each cigarette makes the same contribution to his death,
each cigarette has cost him, on average, 11 minutes of life:6.5 years=2374 days,
56 976 hours, or 3 418 560 minutes 5772 cigarettes per year for 54 years=311 688
cigarettes3 418 560/311 688=11 minutes per cigarette.

This calculation is admittedly crude—it relies on averages, assumes that the health
effects of smoking are evenly spread throughout a smoker's lifetime, presupposes
that the number of cigarettes smoked throughout a lifetime is constant, and ignores
 the difficulties in classifying people as either lifetime smokers or non-smokers.5

However, it shows the high cost of smoking in a way that everyone can understand.
The first day of the year is traditionally a time when many smokers try to stop,
and on 1 January 2000 a record number might be expected to try to start the new
millennium more healthily. The fact that each cigarette they smoke reduces their
life by 11 minutes may spur them on. The table shows some better uses for
the time they save.

1. Doll R, Peto R, Wheatley K, Gray R, Sutherland I. Mortality in relation to smoking:
40 years' observations on male British doctors. BMJ. 1994;309:901–911. [PMC free article] [PubMed]
2. Phillips AN, Wannamethee SG, Walker M, Thomson A, Davey Smith G. Life expectancy
in men who have never smoked and those who have smoked continuously: 15 year follow
up of large cohort of middle aged British men. BMJ. 1996;313:907–908. [PMC free article] [PubMed]
3. Office for National Statistics. 1997 mortality statistics: general. London:
Stationery Office; 1999. (Series DH1 No 30.)
4. Office for National Statistics. General household survey. Living in Britain.
London: Stationery Office; 1996.
5. Suidicani P, Hein HO, Gyntelberg F. Mortality and morbidity of potentially
misclassified smokers. Int J Epidemiol. 1997;26:321–327. [PubMed]


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