LONDON (AP) -- Men in Iceland and women in Cyprus have the lowest risk of dying worldwide, a new study says.

In a survey from 1970 to 2010, researchers found a widening gap between countries with the highest and lowest premature death rates in adults aged 15 to 60. The study was published Friday in the medical journal, Lancet.

The findings are in contrast to the trends in child and maternal mortality, where rates are mostly dropping worldwide. Health officials have long thought if child deaths were decreasing and health systems were improving, adult deaths would similarly decline. But that's not what researchers found.

"The new analysis challenges the common theories," wrote Ai Koyanagi and Kenji Shibuya of the department of global health policy at the University of Tokyo, in an accompanying commentary. They were not linked to the study. Koyanagi and Shibuya said it wasn't clear why there were such major differences among countries in adult deaths.

Researchers in Australia and the U.S. calculated death rates in 187 countries using records from government registries, censuses, household surveys and other sources. It was paid for by the Bill & Melinda Gates Foundation.

Only a few countries have cut death rates by more than 2 percent per year in the last 40 years: Australia, Italy, South Korea, Chile, Tunisia and Algeria. The U.S. lagged significantly behind, dropping to 49th in the rankings for women and 45th for men. That puts it behind all of Western Europe as well as countries including Peru, Chile and Libya.

"The U.S. is definitely on the wrong trajectory," said Chris Murray, director of the Institute for Health Metrics at the University of Washington, one of the study's authors. "(The US) spends the most on health out of all countries, but (it) is apparently spending on the wrong things."

Murray said they weren't sure why some countries -- like Australia and South Korea -- were particularly successful in reducing death rates, but guessed better policies on things like tobacco control and road accidents might be responsible.

Death rates were highest for men in Swaziland and for women in Zambia. Researchers also found death rates jumped in eastern Europe, perhaps because health systems fell apart after the collapse of the Soviet Union and widespread smoking. In sub-Saharan Africa, deaths have fallen, possibly due to the rollout of lifesaving AIDS drugs.

Murray said adult deaths have largely been neglected by the U.N., except for AIDS and tuberculosis programs. "We need to recognize just how bad things are getting in some parts of the world," he said.

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