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© REUTERS/Camilla Svensk/HandoutJonas Frisén of Sweden's Karolinska Institute in an undated photo.

London-- Scientists said on Thursday they had shown the human body regenerates heart cells at a rate of about one percent a year, a discovery that could one day reduce the need for transplants.

The study of 50 volunteers, using a dating method that detects traces of a carbon isotope left by Cold War nuclear bomb tests, raises the prospect of artificially stimulating the renewal process some day, they reported in the journal Science.

"It would be a way to try and help the heart to some self-help rather than transplanting new cells," Jonas Frisen of Sweden's Karolinska Institute said in a telephone interview.

"Taking advantage of the heart's own capacity to generate new cells either using pharmaceutical compounds or, if it is possible, by exercise or any other environmental factor."

Heart cells are unusual in that they stop dividing early in life. Doctors knew there were master cells called stem cells in the heart, but heart muscle usually simply forms scar tissue after damage and never fully regenerates.

In their four-year study, Frisen and colleagues employed an ingenious method to find out whether there is any regeneration at all.

"The DNA of all plant and animal cells incorporated high concentrations of carbon-14 released into the atmosphere by above-ground nuclear testing during the Cold War, and this unfortunate episode provides a unique opportunity to test cell population dynamics in human tissues," Charles Murry of the University of Washington and Richard Lee of Harvard Medical School wrote in a commentary.

Carbon-14 dating showed that overall, the hearts of their 50 volunteers were "younger" than the patients' ages.

Frisen said the rate at which the new cells are produced slows as we get older, with a young adult in their twenties renewing cells at a rate of about 1 percent a year, falling to half a percent a year by the age of 75.

"If you exchange cells at this rate it means that even if you live a very long life you will not have exchanged more than 50 percent of your cells," said Frisen.

"So at any given time your heart is a mosaic of cells you carry with you from birth and cells that that have been added later to replace cells that have been lost during life."

The finding could also help scientists determine whether some people are predisposed to heart disease, by looking at the heart's ability to renew cells.

"We are interested in studying whether some heart diseases could potentially be caused by too low an ability to replace heart cells," Frisen added.