With a return to the moon and a trip to Mars on the horizon, scientists are studying what effect longer space missions will have on astronauts’ health.

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Buzz Aldrin goes for a walk near the lunar module during the Apollo 11 mission. Getty Images

July 20, 2019, marks the 50th anniversary of the Apollo 11 moon landing.

With a return to the moon and a future mission to Mars moving closer to reality, scientists are focused on what will happen to astronauts’ bodies during these longer missions.

The human body undergoes many changes during spaceflight — from shifts in the heart and blood vessels to the bacteria in the gut.

Some changes are minor or return to normal when astronauts are back on Earth. But others could affect astronauts’ long-term health or their ability to function on the moon or Mars.

Ionizing radiation is a top concern for astronauts because it can damage DNA and other molecules in the body.

“Radiation isn’t such a problem during the mission, but the fear is that astronauts might have higher rates of cancer after the mission,” said Alan Hargens, PhD, a professor and director of the Orthopaedic Clinical Physiology Lab at the University of California in San Diego.

In space, ionizing radiation comes from solar flares and cosmic rays. It’s also present on Earth, emitted in smaller amounts from radioactive materials.

Current understanding of the effects of radiation on astronauts was recently boosted by the completion of a long-term NASA study of a pair of astronaut twins. Scott Kelly spent a year on the International Space Station, while his brother Mark Kelly remained on Earth as a “ground control” subject.

The study, which was published April 12 in the journal Science, found that Scott’s DNA changed in ways that fits with damage caused by exposure to space radiation.

These changes remained even up to six months after he returned to Earth — which was the end of the current study.

The Earth’s magnetic field and atmosphere protects people on the ground from ionizing radiation. Because of its low orbit, the International Space Station also receives some protection from the Earth’s magnetic field.

But as astronauts move further away from Earth, this protection diminishes. Even less is known about the radiation hazards astronauts will face on a three-year Mars mission.

Researchers also tested Scott’s and Mark’s thinking abilities using a series of 10 computerized tests.

While in space, Scott’s combined speed and accuracy for these tests — known as cognitive efficiency — was similar to his brother Mark’s performance during this time.

But after returning to Earth, Scott’s speed and accuracy decreased for most of the tests. His cognitive efficiency was also lower than his brother’s. These declines lasted for up to six months.

These effects weren’t alarming, and Scott adjusted well after returning to Earth. But it raises a possible “red flag” for missions to the moon or Mars, where astronauts would have to perform a number of technically challenging operations after landing.

Of around 300 astronauts surveyed, 29 percent who completed short-duration missions and 60 percent who did long-duration missions reported vision problems.

Hargens said, “Some of the vision impairment that astronauts get during long-duration spaceflight continues for over a year after they come back.”

Scientists don’t know exactly how this condition, known as spaceflight-associated neuro-ocular syndrome (SANS), develops. Hargens said it may be due to a shift of body fluids toward the head in weightlessness.

On Earth, when you stand or sit, gravity pulls fluids toward your feet. When you lie down, fluids shift toward your head — which is also what happens with no or low gravity.

Hargen’s group is testing special chambers on Earth that reduce the air pressure on the lower body. This simulates the effect of gravity on body fluids.

They found that people who spent just a short time in one of these chambers had decreased pressure inside the skull and the jugular vein in the neck.

Long-duration spaceflight also causes changes similar to a lack of physical activity on Earth.

“Significant changes in cardiorespiratory fitness, muscle mass and function, and cardiovascular function are known to occur with spaceflight,” said Carl Ade, PhD, an assistant professor of exercise physiology at Kansas State University in Manhattan, Kansas.

But he said research suggests that the body can recover from many of these changes after astronauts return to Earth. So far, though, this is mainly based on space missions shorter than a year.

Ade said many questions remain about longer missions, such as whether the changes will be large enough that they put astronauts at risk, or whether astronauts will recover in the partial gravity of the moon or Mars.

Astronauts may be able to minimize these effects with special diets, medications, and exercise most of all.

“Not surprisingly, exercise is one of the best therapeutic strategies we have for maintaining astronaut health,” Ade said.

“The challenge is determining how much and what type is the most effective.”

Researchers are also looking for ways to simulate gravity during exercise — to give the body a full weight-bearing workout.

One sci-fi favorite is a rotating spacecraft, which produces the feeling of gravity on the inside of the ship’s outer walls. But this is a long way from reality.

Hargen’s group has another option: Put a treadmill inside a lower-body negative pressure chamber. Their results show that this seems to reduce some of the bone loss caused by weightlessness.

Exercise may also help with another common problem astronauts face when they return to Earth: dizziness and fainting due to a drop in blood pressure when standing up.

A new study published today in Circulation found that astronauts who did daily endurance and resistance exercise training while in space and received intravenous fluids upon landing didn’t suffer from this kind of low blood pressure.

Many of the technological advances needed to put people in space over the past 50-plus years have benefited the rest of us on Earth — from freeze-dried food to improved radial tires.

Ade expects the medical advances needed to keep astronauts healthy on long missions will have the same effect.

First, there’s the super-long-distance telemedicine needed for these missions. If you can communicate with your Earth-based doctor from Mars, why not from your house in the mountains of Colorado?

There are also direct benefits of this research.

“If we can improve an astronaut’s cardiovascular, nervous, and musculoskeletal health when they’re in the confines of a long-duration spacecraft,” Ade said, “then we can take that knowledge and technology and apply it to people who are confined to at-home care or a bed.”