Oct. 2 (Bloomberg) -- More than half of babies born today in rich nations will live for 100 years as earlier diagnoses and better treatment of illnesses such as heart disease extend lives, scientists estimate.

Life expectancy increased by three decades or more over the 20th century in countries such as the U.S., U.K., France, Germany, Canada and Japan, and that trend will continue, according to a review published today in The Lancet medical journal. Without any further improvement in longevity, three- quarters of babies will mark their 75th birthdays, the Danish and German researchers wrote.

“The linear increase in record life expectancy for more than 165 years does not suggest a looming limit to human lifespan,” wrote lead researcher Kaare Christensen, a professor at the University of Southern Denmark’s Danish Ageing Research Centre, in the review.

Better health care for the elderly, particularly in the U.S., has extended lives by making illnesses like heart disease manageable over time and allowing earlier detection and intervention, the authors said. Public health campaigns against smoking have also aided longevity, they said.

People are also living longer without becoming severely disabled, the scientists said, citing four health surveys in France.

The aging of society has left nations struggling with how to fund programs for older citizens, the reviewers said. In Germany, the number of elderly for every 100 working-age people has risen from 16 in 1956 to 29 in 2006, and is forecast to reach 60 by 2056, the researchers said.

Shorter Work Weeks

Shortened work weeks over longer working lives may further extend longevity, they wrote.

“If people in their 60s and early 70s worked much more than they do nowadays, then most people could work fewer hours per week than is currently common,” the researchers said.

Such a redistribution of employment might help countries cope with the economic demands of an aging society, though it won’t be enough to meet those demands, they said.

Christensen and colleagues from the University of Rostock and the Max Planck Institute for Demographic Research, both in Germany, based their review on data available since 2004. The research was funded by a grant from the U.S. National Institutes of Health in Bethesda, Maryland. The Danish Ageing Research Centre gets support from the Velux Foundation, based in Switzerland.

To contact the reporter on this story: Kristen Hallam in London at khallam@bloomberg.net

Last Updated: October 1, 2009 18:30 EDT