Student Projects

Independent-learning super-curriculum projects: reading, research and ideas shared by Perse students

How Space Affects Astronauts’ Bodies

Charlotte H – Y7

Living and working in space with zero gravity is a dangerous matter. Being in zero gravity affects an astronaut’s muscular, skeletal and vestibular (sensory) systems. Before they leave, astronauts have to learn how to control all of these problems. Some of the things that happen to their bodies, scientists are still exploring.

Space creates a lot of problems to the human bodies, this is largely due to the fact that up in space, there is no gravitational pull and so the body doesn’t have to work as hard to function as it does down on earth. One of the consequences of this that scientists have discovered is that space makes you ‘grow’ no matter what age you are. Muscles will relax and extend because there is no gravitational pull down on them.  Another of the quirky things that happen to astronauts is known as ‘Puffy heads and bird legs’. Two thirds of our bodies are made up of fluids. On Earth, gravity pulls most of this towards our legs. In zero gravity, fluids naturally travel upwards into our face and head, causing them to puff up and look swollen.


This gives astronauts ‘puffy face syndrome’. The extra fluid in the head may lead to blocked noses and ears, however once astronauts are back on Earth, they return to their normal appearance. This fluid shift can result in the loss of about a litre of fluid in each leg, creating very thin legs which are known as ‘bird legs’. The fluid movement in zero gravity causes blood pressure to equalize at about 100 mmHg throughout the body, whereas on earth the blood pressure on the brain is lower than in the feet. This shift in blood pressure sends a warning signal to our brains. Our bodies expect a blood pressure gradient. Higher blood pressure in the head raises an alarm: The body has too much blood! Within two to three days of weightlessness, astronauts can lose as much as 22 percent of their blood volume as a result of that important message. This change also affects an astronaut’s heart. If they have less blood, then their hearts don’t need to pump as hard and heart rates slow down.

While in space, astronauts lose a lot of calcium essential to their bones which makes them weaker and more fragile – it’s a bit like osteoporosis here on Earth! Osteoporosis is when your bones go fragile and brittle because of the loss of calcium or vitamin D. Scientists believe that this is caused by the lack of ‘load-bearing exercise’ e.g. running, walking, lifting or anything that works against earth’s gravitational pull. After five months in orbit above the Earth, an astronaut would typically lose as much as 40% of muscle and 12% of bone mass. To minimise this as much as possible, astronauts do exercise every day attached to bungees or springs to mimic the gravitational resistance. British astronaut Helen Sharman OBE spent 8 days on the Russian Mir space station in 1991. Whilst in space she conducted research on bone loss by taking various blood samples over the course of her expedition. These samples were combined with samples from other astronauts as well. The research was published several years later showing that calcium was not being absorbed by the astronauts’ intestines and that the bone was being broken down and re-absorbed elsewhere into the body. The authors of the research suggested this was due to a lack of vitamins (eg. Vitamin D and Vitamin K) which are essential for calcium absorption and healthy bones.


When astronauts return to Earth, they will experience problems standing up and balancing because of the effects of space on their vestibular system. As well as this, astronauts’ ‘hand eye coordination’ will worsen whilst in space. This is due to the fact that your inner ear tells you when you are stopped, moving, which way is up, which way is down, when you are standing on your head and when you are lying on your side. When you are in space this stops working so well because there is no gravity telling the inner ear which way is down, so it gets all confused. Astronauts will also experience motion sickness when they first enter zero gravity for the same reason.


Astronauts are likely to face a loss of nutrition due to the fact that the food equivalents aren’t as great up in space as they are down on Earth. It used to be believed that the astronauts’ bones start to perish because they lose lots of iron when they are in space. However, since we now know their blood volume contracts in zero gravity, they actually have a higher storage and therefore the blood that they do have is highly packed with iron. When astronauts are in space they don’t get vitamin D because the sun can’t reach them while they are working. To help the vitamin D intake, astronauts will do short ‘sun bathes’ however in space you are more vulnerable to the sun’s UV rays because there is no protective shield like there is on earth. When astronauts are in space they therefore have to be careful they aren’t in the sun for too long or it could be extremely dangerous. When astronauts go into space they take with them dried food because the fresh food would go off during their time in the space station. This dried food loses most of the vitamins and minerals as it gets dried and then stays in plastic bags in the space station before it gets eaten. Nutritionists plan astronaut meals to make sure they get as much of the nutrients and vitamins they need to perform their important work in space, however despite taking daily vitamin supplements, astronauts will never get all of the vitamins that they need. Some astronauts begin to experience digestive problems after they’ve been in space a long time. Experts believe these problems may be caused by a decrease in the number of “good” bacteria in astronauts’ bodies as a result of not eating enough fibre.


Astronauts have trouble sleeping whilst in space. Those that have returned from space have reported seeing flashes of light zap through their eyes as they try to rest, making it difficult for them to sleep on the space station. These flashes are actually from cosmic rays — high-energy particles that beam through the solar system — shooting through the orbiting outpost. Astronauts have described the flashes as “fireworks” or “streaks.” A lack of sleep can itself have detrimental effects on the body.


The problems don’t end once astronauts return home. In fact, most astronauts have more trouble re-adapting to Earth’s gravity than adapting to microgravity in orbit. Sometimes, astronauts will drop things, forgetting that gravity is influential back on Earth. After six months in microgravity conditions, it is difficult to adjust to life in a place where materials fall if you drop them. They also have to get used to normal balance which takes a while. Sometimes astronauts won’t be able to drive a car to begin with due to the problems with balancing and self-awareness. Their muscles and bones will have weakened, making it difficult to walk and the heart has to recondition itself to pump blood harder to overcome gravity. Each of the astronauts have their own normal recovery time however this will vary depending on the astronaut. One of the quickest things to return is the blood volume which is typically restored within a few days. Astronauts get thirstier than normal when returning from space because of the loss of blood volume, so when they return they have to regain this. The main way to this is by drinking lots of water. Muscle, too, can be recouped. Most comes back “within a month or so, “although it might take longer to recover completely after they return from space. Bone recovery has proven problematic though. For a three to six month space flight it might require two to three years to regain lost bone – if indeed it is going to come back, and some studies have suggested that it doesn’t. You really have to exercise a lot as it won’t just ‘grow’ on its own.

Despite the negative effects of zero gravity, most astronauts say being in space and experiencing weightlessness is amazing. When asked about this, Helen Sharman said “Weightlessness is the most natural, free, relaxing feeling I have experienced. Although it feels uncomfortable to start with, the human body quickly adapts and I forgot what it was like to have weight i.e. to sit down and stand up. Sleeping on the wall or the ceiling is an entirely reasonable thing to do in space!”



Email to Helen Sharman

Scientific Paper: “Bone markers, Calcium Metabolism and Calcium Kinetics during extended duration space flight on the Mir Space Station” Journal of Bone and Mineral Research, 2004



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