Human heart adapts to space by shrinking 27%

Astronaut Scott Kelly jetted off on the adventure of a lifetime on March 27, 2015, where he spent an historic 340-day mission aboard the International Space Station. Kelly made sure to stay active by exercising six days a week with the help of a treadmill, a stationary bicycle, and a resistance machine. Upon his return, however, a scientific study reveals that his heart shrunk by a third, with the official results published in the journal Circulation on Monday, March 29 2021.

The study explains that due to the lack of gravity in space, the human body typically undergoes a number of transformations. Some of these transformations include a swollen head, shrivelled legs, and bones that become more brittle. Interestingly, the study reveals that another transformation came in the largest chamber of Kelly’s heart which caused it to shrink in mass from 189g to 139g - a decline of roughly 27%.

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Dr. Benjamin D. Levine, the senior author of the study and a professor of internal medicine at the University of Texas Southwestern Medical Center and Texas Health Presbyterian Dallas, explains that the change didn’t seem to have any negative effects on the astronaut.

“His heart adapted to the reduced gravity. It didn’t become dysfunctional, the excess capacity didn’t get reduced to a critical level. He remained reasonably fit. His heart shrank and atrophied kind of as you’d expect from going into space,” De Levine says.

Kelly admits that he pushed himself when it came to his exercise regime upon the International Space Station, but that the lack of gravity meant that his heart did not have to pump as hard and, therefore, lost some of its fitness from less strenuous use.

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Dr Levine explains that the shrinkage may be a cause of concern for future missions of that length. He says astronauts will “probably be okay but problems may arise if an astronaut became injured, sick or could not exercise.” 

When he returned home, Kelly said that he didn’t have “any [physical] symptoms from being in space.” He adds “Today, if you let me, I’d go do it all over again.” 

As a result of the discovery, NASA has provided financing to study the heart health of the next 10 astronauts who spend a year in space. 

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Image courtesy: NASA