Explore - Health in Space

Effects of Space on the Human Body

Presentations: These are intended to provide background information for program providers, and not to be used directly in youth programs. These external resources are not necessarily 508 compliant.

  Human Space Travel: Medical Challenges Present and Future (4 MB PowerPoint)
Dr. Diane Byerly

  Space Radiation (13 MB PowerPoint)
Dr. Honglu Wu

  NASA's Plans for Space Exploration (14 MB Powerpoint)
Dr. Stephanie Shipp

  Space Nutrition (12 MB PowerPoint)
Dr. Sara Zwart, NASA Johnson Space Center

On Earth and in space we must maintain our health to perform our everyday tasks well. We need to eat well, exercise, stay clean, get enough sleep, relax, avoid too much sun, and more! While there are many commonalities for staying healthy shared by children and astronauts, living and working in space puts some unique twists on health issues.

Eat Right!

Eating well-balanced diets contributes to our physical and mental health. So is junk food allowed in space? You bet! Dr. Scott Smith, the leader of the Nutritional Biochemistry Laboratory at NASA's Johnson Space Center says, "You can eat any food in moderation! You just need to be sure that you are getting a balance of different foods." Astronauts take some special things to eat on board the spacecraft. Favorites include M&Ms, candy bars, and beef jerky. Even astronauts get the munchies!

Astronauts need well-balanced diets as well, but they face some special challenges caused by changes in the way their bodies function in space.

Expedition Science Officer Ed Lu

Expedition Science Officer Ed Lu uses chopsticks to hold a piece of food and with a drink packet floating in front of him.
Credit: NASA, ISS007E14837, Food in Space Gallery

Getting Enough to Eat. Many astronauts find that they are just not as hungry or the food is not as appetizing, or they are too busy to eat when they are in space. Most lose about 5% of their weight during a typical Space Station stay of 4 to 6 months. While not life threatening at these levels, they are encouraged by the medical team to eat balanced meals even when they are not hungry, and to eat higher calorie foods. To help ensure appetizing menus, the astronauts taste-test the food and select their personal menus well before blasting off into space. Menu selections help design meals that are balanced with the needed amount of vitamins, minerals and calories.

Wanted: Calcium. More than half of our living bone material is made of calcium and phosphorous. Bones are our body's "calcium bank" — calcium is constantly being taken out to use for other bodily processes. There is a constant balance of osteoblasts (the bone-forming cells) and osteoclasts (the bone resorbing cells) and osteocytes (the bone maintaining cells). We need to consume lots of calcium to maintain healthy bones, and keep the activity of these three cells in balance.

In space, the lack of gravity signals the osteoclasts to begin breaking down the unnecessary bone and the osteoblasts either don't change or slow their production of new bone. The net result is for a loss of bone mineral. Astronauts lose 1 to 2% of their bone mass for each month they are in space. Bone mass loss — on Earth or in space — means that bones become weaker and they fracture and break more easily when stressed. To counter bone mass loss, astronauts eat a diet rich in calcium. Once the astronauts return to Earth, the bone loss stops. Scientists are working to understand if the lost bone is completely replaced and if the new bone is the same strength or weaker than the original.

Vitamin D Dilemma. Our skin uses small amounts of natural ultraviolet radiation to manufacture vitamin D, which — like calcium — is vital to maintaining healthy bones. About 10 minutes of Sun each day allows our skin to make the recommended amount of vitamin D. To work outside in the space environment, astronauts have to wear space suits which shield them from ultraviolet radiation. So because astronauts cannot produce vitamin D naturally from sun exposure, they take supplements to help with this issue.

Iron in the Extreme: Astronauts accumulate iron in their body; likely related to a few causes. Upon entering weightlessness, the body begins to reduce the number of red blood cells and the volume of blood in the circulation, perhaps because it is easier to pump blood through the body in microgravity conditions. The iron from the excess blood samples is stored in places like the liver. Too much iron can be harmful, and reducing the amount of iron in the body is hard — as typically (on Earth) the body struggles to get enough iron.

Fabulous Folate: Folate is an important vitamin, and among other functions, it helps to repair cellular damage from high energy solar radiation and from the pure oxygen astronauts breathe at times during their flight (such as during space walks). Astronauts eat diets rich in folate. — but there are concerns that the vitamins in food may not be stable in the radiation environment.

Healthy Hydration: Water makes up about 2/3 of our weight. Our cells need water to create the chemical reactions that sustain us, and water in our blood helps our circulatory system carry nutrients. Water helps to carry toxins out of our bodies. Everyone — including astronauts — loses water when they sweat, go to the bathroom, and even when they breathe. Astronauts, like children on Earth, have to drink lots of water to keep their bodies functioning well. Six to 8 glasses of water are recommended for children and astronauts each day.


Exercise keeps our heart healthy, makes our muscles and bones stronger, keeps us flexible, and makes us feel better all around. On Earth, gravity pulls against us when we walk, run, and play ball — this makes our muscles work hard — and keeps them strong! It also stresses our bones and tells our bone cells to continue to make more bone. But in space, astronauts float around and don't have to use their muscles nearly as much and they don't need their bones to help support them. On the Space Station objects have no weight — and little effort is required to lift things or move around. Standing, walking, and even breathing on Earth requires more muscle and bone strength than in space.

Because astronauts don't need as much muscle and bone in space, their body stops maintaining them — their muscles atrophy (even their heart muscles get smaller because the heart does not have to pump as hard in microgravity) and their bones deteriorate. Astronauts have to exercise — almost 2 hours a day! — to make their muscles and bones physically work and stay healthy for their return to Earth.

Astronaut Peggy Whitson

Astronaut Peggy Whitson exercises during her stay aboard the International Space Station.
Credit: NASA, Your Body in Space: Use it or Lose It

What kind of exercises do astronauts do? They perform "resistive" exercises; they pull against the exercise machines in various ways — making it seem like they are lifting weights with their arms and legs. They also pedal on a recumbent stationary bicycle and walk and run on a treadmill. The bicycle and treadmill can be programmed to provide resistance to their pedaling or walking, so they get quite a workout even in microgravity. Astronauts always have to be attached to the machines — to keep from floating away! Even with this much exercise, astronauts still experience muscle and bone loss and have to build their muscles when they are back home.

On Earth, we also need to exercise to maintain healthy and strong muscles and bones. If you stay in bed for a long time — a month or more — when you finally get out, your muscles are very weak and you will tire quickly. So stay active!

Stay Clean!

Staying clean helps to prevent the spread of germs and diseases — at home or in space. On Earth, this means bathing, washing our hands, brushing our teeth, and wiping dirty surfaces with disinfectant. In space, it means the same thing, only different ways to do so! You cannot have free-flowing water in space; in microgravity, the water does not simply flow down the drain! Astronauts use sanitizing wipes to keep their bodies and hands clean. They use rinse-less shampoo to wash their hair; just rub it in and towel it off! To brush their teeth astronauts can either swallow the toothpaste (yuck) or spit it into a wipe or cloth. Dishes and surfaces are cleaned with sanitizing wipes.

NASA/Mir-23 researcher Jerry Linenger

NASA/Mir-23 researcher Jerry Linenger brushes his teeth while other personal hygiene items float around him — including toothpaste, deodorant, brush and Astro gel.
Credit: NASA, Welcome to Shuttle Mir

Sleep Well!

Getting plenty of sleep helps our bodies to rest and recover from activity and keeps our brains thinking clearly when we are awake. Eight hours is the recommended number of hours of sleep each day for children and for astronauts! However, children often are tucked into their beds and astronauts are strapped into theirs. In microgravity astronauts float; their movements need to be restricted so that they do not bump into places they shouldn't. Like on Earth, it can be hard to get a full 8 hours of sleep in space. It is exciting to be in space, and who wants to miss the adventure by sleeping through it? Daylight is also an issue; because the Space Station is going around Earth at a high rate of speed, the Sun rises every 90 minutes. This pattern of darkness and sunlight can be disruptive to sleep; astronauts pack sleep masks. Physical changes that the astronauts' bodies go through in space — lengthening of their spines, shifting of their fluids — can cause discomfort that prohibits sleep as well. And finally, sometimes the job underway requires the crew to work shifts; it's hard to sleep when your team mates are banging around and talking! Once the astronauts are back on Earth, their sleep patterns return to normal.

Graph showing number of asteroids and time billions of years ago

Astronauts Frederick Sturckow (top), pilot, and Jerry Ross, mission specialist, strap themselves into sleeping bags to prevent themselves from floating around the Space Shuttle while they snooze. Credit: NASA, Living in Space

Stand on Your Head!

Not really. On Earth, our blood tends to go toward our feet because of the pull of gravity. Our strong heart muscle keeps the blood circulating. In microgravity, however, our internal fluids — those in our cells and blood — shift from our legs toward our heads. Astronauts suffer from shrunken legs and puffy heads very soon after going into space. This can cause headaches and stuffy heads.

Astronauts also grow taller! Our spines — backbones — are made of 33 vertebrae that are separated by thin pads of tough fiber (inter-vertebral discs). This inter-layering of bone and disk allows our spines to be flexible — letting us bend and twist, but still protecting the important nerves in our spinal cord. Earth's gravitational force compresses our spines; we do not sense the compression because we are used to it. But in microgravity settings this compressive force is no longer present — and our spines stretch! Astronauts actually grow 2 to 3 inches taller (5 to 8 centimeters) when they are in space! The stretching can cause them some pain; many astronauts have back pain while they are in space and the stretching can potentially injure nerves.
Unfortunately, there is little that can be done for any of these conditions — from swollen heads to increased height; astronauts just have to tough it out until they get back to Earth and the conditions go away.

Stay Balanced!

On Earth we know where "down" is. You fall there. In microgravity, however, there is no "up" or "down." Our inner ear contains tiny "motion detectors" that — along with information from our eyes, ears, and skin — send signals to our brain about our condition of motion and balance. Without a key, such as "down," our sensitive systems have a difficult time sensing our orientation. Indeed, astronauts often feel disoriented and upside down — they are suffering from "space adaptation syndrome." Many astronauts have nausea, vomiting, and headaches that disappear after the first few days of space travel.

Use Sun Block!

Our Sun produces many types of energy, some of which is dangerous to humans and other organisms because it can damage our tissue. Much — not all — of this dangerous radiation is filtered by our atmosphere. Some ultraviolet radiation passes through our atmosphere. While we cannot see or feel this ultraviolet energy, it interacts with our tissue. On the plus side, it helps our skin manufacture vitamin D, a necessary vitamin for bone production and immune system health. However, too much ultraviolet radiation causes our skin to burn. On Earth, we can protect ourselves by wearing clothing, using sun block, and staying out of the Sun.

Astronauts work above Earth's protective atmosphere and are exposed to high levels of ultraviolet radiation and other radiation such as high energy X-rays, and gamma-rays and even more dangerous cosmic rays. Ultraviolet radiation is not as much of a concern; they work in spacecraft that have special shielding, wear special suits when they work outside of the spaceship, and even have special visors to protect their eyes. This equipment has been coated with special UV-blockers.

Lunar rocks

Astronaut James H. Newman is protected from harmful ultraviolet radiation by the spacesuit and specially coated visor on the helmet. The spacecraft also protects the astronauts from some of the radiation in space.
Credit: NASA, STS088-E-5056 (12-07-98), STS-88 Shuttle Mission Imagery

However, some high energy radiation can still pass through the shielding. Astronauts receive 10x the amount of radiation exposure as we do on Earth. Such high exposure can damage the immune system, causing astronauts to be susceptible to infection while in space. Long-term exposure can damage cells and DNA, leading to cataracts and cancers. Astronauts wear instruments, called dosimeters, that monitor how much radiation each of them has received. Once they reach certain levels, they do not continue to work in space. NASA and other space agencies are exploring the effects of radiation and testing different materials that may be used in suits and spacecraft to protect space travelers from radiation.

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