2013年1月22日 星期二

Lifespan and the sexes 已開發國家的兩性平均壽命漸相近


2013-01-21 Web only 作者：經濟學人
第 三大因素則是肥胖，或是肥胖帶來的健康問題。表面上來看，兩性的肥胖率差別不大，但肥胖對女性的影響可能比較大；肥胖會提升高血壓和糖尿病的風險，而且女 性的升幅高於男性。另一方面，因心血管疾病而死亡的男女性都減少超過50%，但由於男性死亡人數是女性的2倍，所以男性死亡率的降幅也比較高。
兩 性健康最大的生物學差異來自睪固酮，兩性都有睪固酮，只是男性的分泌量較多。睪固酮會增加侵略性和風險行為，也會壓抑免疫系統；這表性男性死於意外和暴力 的機會高於女性，自殺機會也比較高。因此，研究機構指出，就算男性採行更健康的生活方式，到了65歲之時，女性平均壽命還是會比男性高出1-2年。（黃維 德譯）
©The Economist Newspaper Limited 2013

Lifespan and the sexes
In the rich world, men are closing the longevity gap with women.
Jan 12th 2013 |From the print edition

REG DEAN, who died on January 5th at the ripe age of 110, was unusual. Centenarians are rare in themselves, of course, but male centenarians particularly so. In Britain, where Mr Dean lived, five times as many women as men receive the famed card of congratulation from the queen when they celebrate their 100th birthdays. That may, however, cease to be the case in the future, for the fact that women tend to live longer than men, though still true, is less true than it was, and the gap is shrinking—in rich countries, at least—every year.

In England and Wales, the biggest peacetime difference between the life expectancies at birth of the two sexes was 6.3 years. That was in 1967. It is now 4.1 years, and falling. In the early 1980s women who made it to 65, the traditional age of retirement for British men, could expect to live four years longer than their male counterparts. The gap now is less than three years (see chart), though there is still some way to go before things return to the nine-month gap that prevailed in the 1840s, when records began. Other industrialised countries, except Japan and Russia, show something similar.

This trend is superimposed on another: that life expectancy in most developed countries has been improving for both sexes. But of late it has been improving more for men than for women.

A report about to be published by the Longevity Science Advisory Panel (a group of scientists and actuaries set up by Legal & General, an insurance company) examines the factors behind these trends. The biggest by far is changes in the use of tobacco.

All are equal
Around half the difference in the longevity of the sexes can be explained by smoking. One reason why Russia bucks the trend towards equal life expectancies for the two sexes (women there live 12 years longer than men) is that its men have not followed their Western confrères and cut down on the cancer sticks.

In Britain in the 1960s, when the habit was commonplace, men were much more likely to be smokers than women. But they have also been more likely than women to give up cigarettes over the past half-century. As a result, between 1979 and 2009 male smoking-related deaths fell by 64% and the male-to-female ratio of such deaths fell from 2.1 to 1.7. Deaths from cancers of the lung, trachea and bronchus in particular fell by 39% between 1991 and 2005 among Englishmen over 49. For women the comparable figure was 3%.

A further fifth of the longevity gap between the sexes is explained by alcohol. In this case, however, the gap is widening. In 1979 two men died from alcohol-related causes for every woman who succumbed. In 2009 it was 2.4.

A third important factor is obesity—or, rather, the physiological complications obesity brings, such as high blood pressure and type-2 diabetes. On the face of things, there is little difference between the sexes in this area: 15.6% of women in the EU are obese, compared with 15.4% of men. But obesity may have a greater impact on women because it increases the risks of both hypertension and diabetes in their sex more than it does in men. And men are also closing the gap in another area related to obesity and high blood pressure: coronary heart disease. In England, deaths from this fell more than 50% between 1991 and 2005 for both men and women. But, because heart disease kills twice as many men as it does women, the reduction in the male mortality rate has been greater.


A further biological difference between the sexes is in the lengths of their telomeres. These are sections of DNA that protect the ends of chromosomes from decay. Men's telomeres are shorter than those of women, and also degrade more quickly. Both of these attributes have been linked to reduced lifespans.

But some are more equal than others


But blaming testosterone for male risk-taking explains only the "how", not the "why". For that, you must turn to evolutionary biology. It is no coincidence that the gap between the sexes' mortality is widest in people's 20s. This is the peak period for reproduction. Men are fighting each other, and showing off to the girls, in a competition whose prize is, in an evolutionary sense, immortality itself—the passage of their genes to the next generation.


From the print edition: Science and technolog
©The Economist Newspaper Limited 2013