FEW numbers tell a happier story than those that measure life expectancy. An American born in 1900 could expect to live 47 years. Thanks to colossal improvements in sanitation and medicine, that figure is now 75 for men and 80 for women. And the poorest Americans have gained the most: blacks, for example, live more than twice as long now as they did a century ago.
So it is both alarming and surprising when life expectancy falls, even for a small part of the population. Yet that is what some researchers at Harvard have found. They looked at death rates by county, having corrected for migration and merged sparsely populated ones so that America's 3,141 counties became 2,068 “county units”.
For most Americans, life expectancy continues merrily to rise. But between 1983 and 1999, it fell significantly (by about a year) for women in 180 county units, and stagnated in another 783. Men fared less poorly: their life expectancy fell significantly in only 11 county units, and stagnated in another 48.
Put differently, life expectancy appears to have either stagnated or fallen slightly for some 4% of American men and 19% of women. The main culprits are diseases linked to smoking or obesity, such as lung cancer and diabetes. The crucial question is whether this represents a blip or the start of a trend.
Majid Ezzati, one of the study's authors, says it is too soon to say. An optimist would point out that women took up smoking later than men. It was not until after the second world war that they started puffing at anything like the male rate. The bulge of poor women now dying of lung cancer may be a hangover from the end of the taboo on female smoking. But both sexes have quit in droves since the 1970s, so the death toll may fall in the future.
A pessimist would reply that the other big killer, obesity, keeps spreading, especially among the poor. “We've been saying for ages that it must have peaked, but it keeps going up,” says Dr Ezzati. Two decades ago, no state had an obesity rate above 15%. Now, 22 have passed the 25% mark. The counties where life expectancy has fallen are nearly all in the South or Appalachia, where huge deep-fried portions are the norm and waistlines are among America's widest. Neither are getting any smaller. (The Economist, 4.24.2008) http://www.economist.com/world/na/displaystory.cfm?story_id=11089916