Growing older can take a serious toll on the body. Bones become brittle, muscle shrinks, the immune system loses strength, and age-related ailments like arthritis can set in. More serious complications like declining cognitive function and heart disease can also take hold as the later years of life progress.

These symptoms can also come from something less common—space travel. Flying through outer space has dramatic effects on the body, and people in space experience aging at a faster rate than people on Earth. Several papers recently published in the Cell family of journals look at the health hazards that spending time in outer space has had on astronauts. These studies showed that space alters gene function, function of the cell’s powerhouse (mitochondria), and the chemical balance in cells.

Hanging Out in Space Mimics Age-Related Disorders

The health effects of spending time in space resemble some age-related disorders, like cancer and osteoporosis. While the similarities of spaceflight to aging give concern for long-term space missions, like a voyage to Mars, the outer space environment also provides an opportunity to study aging processes in the body.

Scientists estimate that the heart, blood vessels, bones, and muscle deteriorate about 10 times faster in space than in natural aging. In other words, scientists don’t need to wait for their biological study subjects to grow older naturally on Earth—with accelerated health effects in space, they can run experiments on astronauts on the International Space Station (ISS).

But the effects of space travel are not exactly the same as aging, and many of the changes that occur in space reverse themselves when people return to Earth. The comparisons can still be useful, though, and scientists say time spent in space provides a good model for understanding the chronic process of aging. Maybe outer space living could reveal new methods for protecting ourselves from processes that make us grow old.

The Effects of Space Travel

Space affects different cell types in different ways, according to Michael Roberts, interim chief scientist of the ISS National Laboratory in a report in National Geographic. “It’s not a single acute exposure to toxic agents, for example; it’s something that’s long-term, chronic, and persistent.” Space life changes the body’s equilibrium for optimal functioning, thereby rebooting the way that cells respond.

In the microgravity atmosphere of outer space, the heart, bones, and muscle don’t need to work as hard as they do on Earth, so they weaken from disuse. Fluid-filled tissues may change shape because liquid flows differently in microgravity, which can change the shapes of organs like the brain. Not only that but higher background radiation outside of Earth’s atmosphere can cause DNA damage and increase cancer risk.

An Astronaut Twin Study

The new research on the health effects of outer space living started with a study on astronaut twin brothers, Scott and Mark Kelly. Ten research teams monitored changes in Scott’s body during his year-long trip to space. The scientists then compared the changes to Scott’s identical twin brother Mark who stayed on Earth during that time. The research teams recorded differences in the twin astronauts ranging from changes in gene expression profiles, microorganisms in the gut (the microbiome), cognitive abilities, and cardiovascular systems.

A striking discovery from the NASA Twins Study was that Scott’s telomeres changed length. Telomeres are regions of DNA at the ends of chromosomes that protect the rest of the DNA from damage, decay, and fraying. Telomere lengths diminish with age and how quickly they shorten is an important indicator of health and aging.

While Scott was in Space, his telomeres lengthened, but when he returned to Earth, they rapidly shrunk. Although his telomeres were longer during spaceflight, he ended up with shorter telomeres than he started with. Shortened telomeres have been linked to cardiovascular disease while longer telomeres are associated with cancer. So, either of these changes in telomere length can have negative health consequences.

Some of the health effects of spaceflight seem to equilibrate after a certain amount of time in space like decreased blood volume and changes in the lungs and heart. Astronauts haven’t spent enough time on the ISS to say with any certainty whether these changes in the body will reach a steady-state, though.

A Cosmic Opportunity

Thanks to the unique environment that comes from space travel, researchers can now look for creative ways to boost human health. Many health-promoting therapies have come from scientists’ efforts to boost humans’ adaptation to space, like obtaining protein from near-indestructible microorganisms called tardigrades, which could also address aging-related diseases that plague humanity.