National Geographic News
They may not be able to mend a broken heart, but our heart cells are replaced over our lifetimes, a new study says.
The discovery, made by analyzing heart cells irradiated by 1950s nuclear bomb tests, might lead to new heart treatments, scientists say.
It's long been a mystery whether human adults have a set number of heart cells or whether cells are added to replace old ones over time.
As it turns out, heart muscle cells, which are responsible for the contractions that pump blood through our bodies, can in fact renew themselves. The cells regrow at an annual rate of 1 percent at age 25, slowing to about 0.45 percent by age 75, the new study says.
This slow turnover has made it "very difficult" to prove that heart muscle regenerates, said study co-author Jonas Frisén, a cell biologist at Sweden's Karolinska Institutet medical school.
"It's easy to study renewal of short-lived cells," Frisén said, but "if the [cell] exchange rate is low, you cannot use the regular tricks."
So in the new study, researchers employed a "very clever use" of history.
By identifying traces of radiation from aboveground 1950s nuclear bomb tests in people born before the tests, the team determined the irradiated cells must have appeared sometime after birth.
"The bottom line is that, despite the fact we [had] some evidence there is turnover in heart cells, there's been a bit of controversy," Tomaselli said.
"Now this data suggest there is a renewal of heart cells within the heart."
During the nuclear bomb tests of the 1950s, the radioactive carbon isotope carbon-14 dramatically increased in the atmosphere. As a result, everyone alive at the time has traces of carbon-14 in their tissues.
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