5. Cardiovascular Changes
In microgravity, the heart no longer works against gravity to pump blood throughout the body. As a result, it can become more spherical and may even lose muscle mass over time. These changes often lead to lower blood pressure and a condition known as orthostatic intolerance—difficulty standing upright without feeling faint—once astronauts return to Earth. Ongoing research aims to find ways to keep astronauts’ hearts healthy on long-duration missions. [Source: American Heart Association]