The key is muscle-derived stem cells, which—like other stem cells—are unspecialized cells that can become any type of cell in the body.

When injected with muscle stem cells from young mice, older mice with a condition that causes them to age rapidly saw a threefold increase in their life spans, said study co-author Johnny Huard, a stem-cell expert at the McGowan Institute for Regenerative Medicine in Pittsburgh.

(See "Liposuction Fat Turned Into Stem Cells, Study Says.")

"I've been doing science for the last 20 years," Huard said. What "makes the story so amazing is that in the beginning, I didn't believe the result," he said.

"I bet that we mixed up