How a year in space affected Scott Kelly's health | Science News for Students

How a year in space affected Scott Kelly's health

A comparison to his twin looks at how long-term spaceflight changes the human body
May 17, 2019 — 6:45 am EST
A photo of astronauts Scott and Mark Kelly

Astronaut Scott Kelly (left) spent a year in space on the International Space Station while his identical twin brother, astronaut Mark Kelly (right), remained on Earth. They were part of a landmark study to help researchers understand how space flight affects the human body.


For nearly a year, identical twins Scott and Mark Kelly lived in different worlds — literally. Mark enjoyed Earth-bound retirement in Tucson, Ariz. Meanwhile, Scott floated in microgravity aboard the International Space Station some 400 kilometers (250 miles) above the planet. That year apart has given scientists the clearest look yet at how long-term spaceflight can affect the human body.

Ten science teams in NASA’s Twins Study examined the brother astronauts before, during and after Scott’s 340 days in space. The teams studied each twin’s body functions. They ran memory tests. And they examined the men’s genes, looking what differences might be due to space travel.

The long-awaited results appeared April 12 in Science. They confirm that lengthy space travel stresses the human body in many ways. Space living can change genes and send the immune system into overdrive. It can dull mental reasoning and memory.

This is “the most comprehensive view that we’ve ever had of the response of the human body to spaceflight,” says Susan Bailey. She studies radiation and cancer at Colorado State University in Fort Collins. She also led one of the NASA research teams. She says it’s still unclear, however, whether the changes seen will cause long-term harm.

Genes in space

The scientists couldn’t go with Scott when he entered space in March 2015. So he had to help them out. While in orbit, he collected samples of his blood, urine and feces. Other visiting astronauts carried them back to Earth. Then, the research teams ran a host of different tests to analyze various body functions. They compared these data to those taken before and after Scott’s spaceflight.

Scott’s samples from space showed many genetic changes from those taken on Earth. More than 1,000 of his genes had chemical markers that weren’t in his preflight samples or in samples from Mark. These chemical markers are called epigenetic (Ep-ih-jeh-NET-ik) tags. They can be added or removed due to environmental factors. And they affect how genes work. A tag might affect their activity by determining if, when or how long a gene is turned on or off.

Some of Scott’s genes changed more than others. Those with the most epigenetic tags helped regulate DNA, Bailey’s team found. Some handle DNA repair. Others control the length of the tips of chromosomes, called telomeres.  

Telomeres are thought to protect chromosomes. Shortened telomeres have been linked to aging and health risks, such as heart disease and cancer. The scientists had expected Scott’s telomeres might shorten in the low gravity and high radiation of space. So they were surprised to find that they actually had grown — 14.5 percent longer.

That growth didn’t last, however. Within 48 hours of his March 2016 return to Earth, Scott’s telomeres quickly shrank. Within several months, most of them were back to preflight lengths. But some telomeres had gotten even shorter. “That could be where he might be at increased risk” of cancer or other health problems, Bailey says.

a photo of Scott Kelly testing his mental abilities on the International Space Station
Scott Kelly performs a test of mental abilities during his time on the International Space Station. It helped track how spending extensive time in space affects reactions, memory and reasoning. 

Christopher Mason studies human genetics at Weill Cornell Medicine in New York City. His group looked at which genes were affected by spaceflight. In Scott’s early blood samples from space, Mason’s team noted many immune-system genes switched onto active mode. While a body is in space, “the immune system is on almost a high alert as a way to try and understand this new environment,” says Mason.

Scott’s chromosomes also went through many structural changes, another team found. Chromosome parts were swapped, flipped upside down or even merged. Such changes can lead to infertility or certain types of cancer.

Michael Snyder, who led another of the teams, was not surprised by such changes. “These are natural, essential stress responses,” he says. Snyder studies human genetics at Stanford University in California. His group looked for stress-caused shifts in the twins’ immune systems, metabolism and production of proteins. It’s likely that high-energy particles and cosmic rays in space worsened the changes in Scott’s chromosomes, Snyder says.

Lasting effects

Most changes that Scott experienced in space reversed once he returned to Earth. But not everything.

The researchers tested Scott again after six months back on land. Roughly 91 percent of the genes that had changed activity in space were now back to normal. The rest stayed in space mode. His immune system, for instance, remained on high alert. DNA-repair genes were still overly active and some of his chromosomes were still topsy-turvy. What’s more, Scott’s mental abilities had declined from preflight levels. He was slower and less accurate on short-term memory and logic tests.

It’s unclear whether these results are definitely from spaceflight. That’s partly because the observations are from only one person. “Bottom line: There’s a ton we don’t know,” Snyder says.

a selfie of Scott Kelly on the International Space Station, to his right is a window showing Earth below
During the NASA Twins Study, Scott Kelly took an image of himself while aboard the International Space Station, where he spent 340 days.

More answers may come from upcoming missions. Last October, NASA funded 25 new projects that each could send up to 10 astronauts on yearlong space missions. And on April 17, NASA announced an extended space visit for U.S. astronaut Christina Koch. She reached the International Space Station in March. This mission, until February 2020, will make her spaceflight the longest yet for a woman.

But to learn how space really impacts health may call for even longer trips. A mission to Mars and back would take an estimated 30 months. It would also send astronauts beyond Earth’s protective magnetic field. That field shields against DNA-damaging radiation from solar flares and cosmic rays.

Only astronauts on the lunar missions have gone beyond Earth’s magnetic field. None of those trips lasted more than a few days each. So no one has spent even one year in that unprotected environment, let alone 2.5 years.

Markus Löbrich works at the Technical University of Darmstadt in Germany. Although not part of the NASA Twins Study, he does research into radiation’s effects on the body. The new data are impressive, he says, but highlight that we are not yet ready for longer-term space travel.

One way to avoid such long space exposures would be to speed up the trip, he notes. Perhaps new ways of propelling rockets through space could reach distant places more quickly. But most of all, he says, sending people to Mars will require better ways to protect people against radiation in space.

Power Words

(more about Power Words)

astronaut     Someone trained to travel into space for research and exploration.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chromosome     A single threadlike piece of coiled DNA found in a cell’s nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.

cosmic rays     Very high-energy particles, mostly protons, that bombard Earth from all directions. These particles originate outside our solar system. They are equivalent to the nucleus of an atom. They travel through space at high rates of speed (often close to the speed of light).

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

epigenetic     An adjective that relates to the molecular switches that can turn a gene on or off. Methyl groups — chemical clusters each made of one carbon and three hydrogen atoms — latch onto DNA near a gene. It’s these methyl groups that can alter the programmed activity of a gene. Individuals can acquire an epigenetic change at any time during their lives.

factor     Something that plays a role in a particular condition or event; a contributor.

feces     A body's solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

gravity     The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

immune     (adj.) Having to do with the immunity. (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

International Space Station     An artificial satellite that orbits Earth. Run by the United States and Russia, this station provides a research laboratory from which scientists can conduct experiments in biology, physics and astronomy — and make observations of Earth.

literally     A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

lunar     Of or relating to Earth’s moon.

magnetic field     An area of influence created by certain materials, called magnets, or by the movement of electric charges.

marker     (in biomedicine) The presence of some substance that usually can only be present because it signals some disease, pollutant or event (such as the attachment of some stain or molecular flag). As such, this substance will serve as a sign — or marker — of that related thing.

Mars     The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

metabolism     (adj. metabolic)  The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.

microgravity     Gravity that is a fraction of the force experienced at sea level on Earth.

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

orbit     The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

radiation     (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

rays     (in biology) Members of the shark family, these kite-shaped fish species resemble a flattened shark with wide fins that resemble wings.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

rocket     Something propelled into the air or through space, sometimes as a weapon of war. A rocket usually is lofted by the release of exhaust gases as some fuel burns. (v.) Something that flings into space at high speed as if fueled by combustion.

short-term memory     (also known as primary memory) The small amount of memory held actively in the mind for a short period of time, such as the series of digits in a telephone number.

solar flare     An explosive event that takes place on the sun when energy that has built up in 'twisted' magnetic fields (usually above sunspots) becomes suddenly released. The energy can in minutes heat to many millions of degrees, emitting a burst of energy. That energy consists of radiation across the electromagnetic spectrum, from gamma rays to radio waves.

stress     (in biology) A factor — such as unusual temperatures, movements, moisture or pollution — that affects the health of a species or ecosystem. (in psychology) A mental, physical, emotional or behavioral reaction to an event or circumstance (stressor) that disturbs a person or animal’s usual state of being or places increased demands on a person or animal; psychological stress can be either positive or negative.

telomere     A natural protective “cap” on the ends of chromosomes, made by successions of a six-nucleotide sequence of chemicals. This chemical sequence is found only on the ends of chromosomes. It’s known as TTAGGG, where each T corresponds to a molecule of thymine, each A is a molecule of adenine and each G is a molecule of guanine. Over time, telomeres shorten as they cell they’re in copies itself. If the telomere length gets too short, the cell stops dividing and dies.


Journal: F.E. Garrett-Bakelman et al. The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight. Science. Vol. 364, April 12, 2019. doi: 10.1126/science.aau8650.