Some of us may label astronauts as heroes, and that’s because they have every right to that title. If you’ve seen the movie Gravity then you already know about the (extreme) risks they face going out into space. But simply living in space can have its risks as well. A recent study found that living in a microgravity environment could accelerate cardiovascular disease and the biological aging of cells among astronauts living at the International Space Station.

Believe it or not, being in space does not mean that there’s no gravity, instead of pulling astronauts and their spacecraft toward earth, it’s pulling them around earth — in orbit — and creates the illusion that gravity is non-existent because everything is moving at the same rate. This is called microgravity.

Researchers from the Institute of Molecular Science and Technologies in Milan, Italy, studied the thin layer of cells that line the interior surface of blood vessels, known as endothelial cells. They conducted deep gene expression and protein analysis on 12 cell cultures at the International Space Station (microgravity) and 12 cultures on Earth (normal gravity) in order to see what the differences in gravitational pressure did to the cells.

They found that after just 10 days, the cells — many of which are involved in cell adhesion — that were subjected to microgravity expressed 1,023 genes differently, and secreted larger amounts of proteins that cause inflammation. What was especially concerning was that the differentially expressed genes promoted oxidative stress. Cells that aren’t able to properly detoxify undergo oxidative stress, which results in increased production of peroxides and free radicals that kill proteins, lipids, DNA, and ultimately the cells themselves.

As a whole, the researchers say that oxidative stress paired with an increased production in inflammatory proteins could cause cardiovascular disease and accelerated cell aging. “Our study further supports the role of oxidative stress in accelerating aging and disease,” Silvia Bradamante, a researcher from the Institute, said in a statement.

Atherosclerosis, one of the cardiovascular diseases mentioned by the researchers, is characterized by the buildup of fats and cholesterol in and on the artery walls. It can lead to other forms of cardiovascular disease, including coronary artery disease, which can cause heart attacks and heart failure.

Astronauts put themselves at risk for many other health conditions as well. Studies have linked space travel to Alzheimer’s disease, eye and brain damage, and sleep disorders, which in turn, can lead to a slew of other conditions.

As we plan to send people deeper into space than ever before, and for longer flights, we’ve got to make sure that they remain in [the] best health possible,” Gerald Weissmann, M.D., editor-in-chief of The FASEB Journal, which the study was published in, said in the statement. “We’ve evolved to rely on gravity to regulate our biology, and without it, our tissues become confused. Worst of all: they age faster!”

Source: Versari S, Longinotti G, Barenghi L, et al. The challenging environment on board the International Space Station affects endothelial cell function by triggering oxidative stress through thioredoxin interacting protein overexpression: the ESA-SPHINX experiment. The FASEB Journal. 2013.