Is it possible for the human heart to shrink and if so, how does this change impact the human body?

Recently, scientists have discovered an unexpected similarity between long-distance swimming and spending a long duration of time in space -- both can cause the human heart to shrink over time!

These findings were based on the experiences of astronaut Scott Kelly, who spent 340 days in space in 2015, and Benoît Lecomte, an athlete who in 2018 swam 1753 miles (2,821 km) across the Pacific Ocean in 159 days. 

The Similarity

The absence of gravity in space means that the heart does not have to work as hard to pump blood through the aorta, the largest blood vessel that supplies oxygen to all parts of our body. As a result, the heart loses muscle mass, causing it to atrophy and reduce in size. 

The study was conducted by Professor Benjamin Levine, a professor of internal medicine at the University of Texas Southwestern Medical Center. He noted that the shrinkage was seen despite the fact that Scott Kelly exercised every day. 

Activities such as long-distance swimming can cause the heart to change similarly. Lecomte spent 5.8 hours swimming every day and then another 8 hours sleeping; therefore, he spent more time in a horizontal position than upright. This reduced the force of gravity acting on his body. 

Fortunately, though, while the heart did shrink in size for Kelly and Lecompte, it was just as strong and continued to function normally for both men. And in both cases, the heart regained its original mass and size after a return to normal daily lives.

This study is crucial as NASA prepares to send astronauts to Mars in the 2030s. Dr. Levine is working with NASA on a program called Cipher, which hopes to collect more information by following ten more astronauts’ year-long trips as well as conducting research on shorter trips to space.