Astronauts’ Blood Vessels Don’t Function Well in Space
published during a full moon.

Living in microgravity is hazardous to astronauts’ health and can affect bones, muscles, motor skills, posture, microbiomes, immune systems, vision, and even genes. A new kinesiology study from Kansas State University (KSU) researchers indicates that the decline of astronauts’ physical health is due in part to blood vessels not being able to function as well as they do on Earth.

Astronauts get a lot of exercise on the ISS in an attempt to offset some of the negative consequences of microgravity. Despite these efforts, the exercise itself is far less effective than it is at 1G—the KSU study found a 30-50% drop in astronauts’ ability to exercise while in space because blood vessels struggle to carry oxygen to the muscles.

blood vessels

Diagram of blood vessel structure. Credit: Kelvin Ma

Astronauts’ bodies can’t take in as much oxygen as they’re used to and as much as muscles need for exercise to be optimally beneficial. When that happens, astronauts experience a widespread decline in physical abilities. “When your cardiovascular function decreases, your aerobic exercise capacity goes down. You can’t perform physically challenging activities anymore,” says Carl Ade, an exercise physiology professor who worked on the study. Scientists previously thought heart function accounted for the decrease in the ability to exercise, and while this study doesn’t contradict that theory, it provides a more complete view of what happens in astronauts’ bodies in space—namely, that other processes account for the drop, particularly “at the level of the microcirculation within capillaries,” according to Ade.

The study involved nine astronauts who served the usual six-month stint on the ISS. Before they launched, they had a baseline exercise test to gauge their exercise capacity, as well as their bodies’ ability to take in and transport oxygen. After the astronauts returned from space, they did the test again. The results indicate that lack of gravity affects the relationship between red blood cells and blood vessel capillaries, but scientists aren’t yet entirely sure how or why that happens.

The study will help scientists devise strategies for keeping astronauts healthy on the ISS and on other long-duration spaceflights and missions, including crewed trips to Mars. Because astronauts need to physically function to complete high-stakes tasks in a variety of different environments, it’s imperative that scientists figure out how to prevent problems that decrease their ability to perform. It may be possible to address the problem with medication or an altered exercise regime. Scientists have recently engineered blood vessels in a lab, which raises other possibilities to combat these effects. The research may also provide insights for cardiac patients on the ground, potentially leading to breakthroughs regarding the treatment or prevention of heart failure.