Study Rejects Concept of Aging Limit

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Human beings are living longer than ever, and the steady increase in life span shows no indication of plateauing, according to a study released today by a UC Berkeley professor.

In a survey in today's issue of the journal Science, UC Berkeley Demography Professor John Wilmoth has presented evidence contradicting the belief that the maximum human life span will eventually level off.

"There was never any solid scientific evidence that there was a maximum life span that was immutable," Wilmoth said yesterday. "What this paper shows is that we're pushing up the maximum as well as the average, so the whole distribution of age has been increasing."

Wilmoth and a team of Swedish researchers studied Sweden's national death records dating back to 1861 and found the number of years a human is capable of living follows a steady upward trend. In the 1860s, the oldest age of death on record centered around 101 years. That number rose to around 108 in the 1990s, and will most likely continue to grow, researchers predict.

"For every year of time we took the national statistics, (we recorded) the oldest age at death for the person that year," Wilmoth said. "Within each year, we take the oldest age of death and we plot those two over time. We plot it and look at the trend and did some statistical analysis."

Analysis of the Swedish data showed that human life expectancy increased slightly until 1970, when the graph shifted upward. Prior to 1969, the maximum age increased approximately 0.44 years per decade. Since then, life span has increased 1.11 years per decade.

The increase in life span is the result of a variety of improvements in many fields, including public health, sanitation and medicine, Wilmoth said. The largest contribution to increased life span is the fact that humans over the age of 70 are healthier now than they have ever been, he said.

"It's actually quite complex," he said. "Elderly people today are healthier in part because they didn't suffer as much disease when they were children and young adults. They were better nourished so they arrive into old age with stronger bodies and better health endowment."

Another contribution to the increase in life span is new technology and treatments available to the elderly, Wilmoth added.

"We have made a lot of progress in treating people, especially in the last 30 years, for cardiovascular disease in older ages and the risk factors for cardiovascular disease like high blood pressure and hypertension," he said. "These sorts of medical interventions have helped extend life span."

Wilmoth's findings oppose the belief that the life span of humans will increase until it hits a maximum. Many believe that the human life span will grow until it reaches the limit of approximately 115 years.

Although scientists have found that cells cultured in labs will die after a specific number of cell divisions, many have been too quick to associate this with humans, Wilmoth said. Cells in the laboratory can replicate approximately 50 times before they die.

"Some people said, 'Then look, that's a kind of clock. Once you've used up all those cell doublings, then life could not go on,'" Wilmoth said. "To be honest, there's a huge gap between that knowledge of the process that takes place in cells and what we know about the human life span. There was never a solid linking the two."

According to Wilmoth, the life span limit has no scientific backing.

"It's hard to say where they got that idea (of leveling off)," he said. "It's a common belief but it's hard to figure out what the source of it is. For some people, it's an article of faith that there's a maximum life span."


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