A 2014 study on 12 astronauts found that the human heart becomes 9.4 percent more spherical after long exposure to weightlessness in space. This could cause heart problems. Dr. James Thomas of NASA explained,
“The heart doesn’t work as hard in space, which can cause a loss of muscle mass. That can have serious consequences after the return to Earth, so we’re looking into whether there are measures that can be taken to prevent or counteract that loss."
Although the damaging changes to the heart are reversed once the astronaut lands on Earth, the long-term effects on the heart are unknown. Researchers are involved in long-term studies as to the effects of space flight on the heart, the results of which may also benefit heart patients on Earth. One study currently being conducted is based on the possible formation of atherosclerosis in astronauts.
Read about nine other health risks to astronauts on deep space missions here.