Science and medicine have pushed human life expectancy to its natural limit, about 85 years, researchers said Thursday.

"Even if we found a cure for most fatal diseases such as heart disease and cancer, the natural degeneration of the body puts a cap of about 85 years on the average age of death," scientists at the University of Chicago and Argonne National Laboratory said.It will remain at 85 "unless major breakthroughs occur in controlling the fundamental rate of aging," they added.

However, not everyone agrees with these findings and they will be questioned by others in the field, according to an expert at the National Institute on Aging.

"The past is littered with examples of people who predicted a cap and were left behind," said Richard Suzman, a health science administrator at the institute. "This is going to be the start of a very hot scientific debate."

The Chicago researchers suggested it is time to move beyond merely keeping people alive longer and look for ways to make the last years of life worth living - the latter already an area of growing concern among experts.

Since the middle of the 19th century, life expectancy in developed nations has nearly doubled - from 40 years to nearly 80. A person born today in Japan can expect to live 79 years on average, 75 years in the United States.

Most of the gains during the past 150 years have come from reductions in infant and maternal childbirth deaths.

S. Jay Olshansky of the Department of Medicine at the University of Chicago, one of three authors of the study published Thursday in Science magazine, added:

"Death rates in children and young adults in the United States are so low that eliminating all causes of death before the age of 50 - about 12.4 percent of all deaths, including accidents - would increase life expectancy at birth by only 3.5 years."

Suzman of the Institute on Aging told Reuters other researchers have come to "very, very different conclusions."

He said some researchers have found that certain Mormon groups in Utah - who abstain from tobacco, alcohol and caffeine - already have life expectancies "well over age 85." Other studies have found islands in Japan where women already can expect to live to 83 with likelihood of living longer if the risk of death from strokes could be eliminated.