STOCKHOLM, Sweden

Swedish scientists have found mice appear to age more quickly after their cells' energy systems have been damaged.

The study, carried out by Nils-Goran Larsson of the Karolinska Institute in Stockholm and summarized in the latest issue of the journal Nature, is the first directly to link signs of aging to genetic damage in mitochondria.

Mice with damaged mitochondria suffered premature hair loss, had thinner bones and less body fat and became infertile.

"Old animals or old humans get exactly the same problems," Larsson said.

In addition to such signs of aging, the animals lived an average of 48 weeks, about a third of the normal life span.

The findings lend support to theories that DNA damage that accumulates during life may be a key cause of aging.

"People have been thinking for a long time that aging is caused, at least in part, by mutations that accumulate in mitochondria," said Cynthia Kenyon, a gerontologist at the University of California, San Francisco.

Every cell contains many mitochondria, which help turn protein and fats into energy. Mitochondria are unusual because they have their own DNA, separate from the DNA in the nucleus of all cells.