How do our bodies change in space?

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Space is one of the most hostile environments a human could be exposed to. The microgravity (very weak gravity), the radiation from the sun and the lack of day and night distinction are all examples of the factors astronauts endure while on space missions. This article will discuss how our bodies change in space as it adapts to this new environment and other changes which may occur as a result of being away from the Earth’s protective atmosphere.

Increase in height Gravity provides a compressive force on the discs between vertebrae of the back. This compressive force is absent in space due to microgravity and therefore these discs expand. On average height can increase by between 5cm-8cm. Unfortunately, this can also have medical implications such as back ache and nervous system problems. Luckily, this increase in height is short lived and reverts back to it’s original value within a few months of an astronauts return to earth and should not result in long term health issues.

Decrease in bone density Microgravity in space changes how astronauts move and massively decreases the weight-bearing function of bones. This is a particular problem in the lower half of the body, where it can lead to bone breakdown which results in a decrease in bone density. Radiation can also contribute to this on missions which leave the orbit of the Earth. Up to 1% of bone mass can be lost each month by astronauts in space, but can be minimized by performing regular exercise. A decrease in bone density can increase the chances of broken bones when back on Earth and although bone loss stops once back on Earth, it is uncertain whether complete regeneration occurs.

Redistribution of fluid On Earth, gravity pulls fluid in the body down, so there is more present in the lower extremities compared to upper parts of the body. Since there is no direction in space, the microgravity which acts on the body acts evenly throughout. This causes a redistribution of fluid throughout the body, as fluid migrates from the legs to the face, resulting in a puffy face and skinny legs. The extra fluid in the face can lead to blocked sinuses and result in ‘space sniffles.’

Decrease in muscle mass

The loss of gravity in space comes with the loss of work and load put on to the muscles that would normally power musculoskeletal abilities e.g. the act of walking. Due to the loss of demand for muscles in the legs for example, results in muscle loss or atrophy (wasting) of the muscles. Despite this, astronauts are now encouraged to take part in ‘in-flight exercise’ that helps to reduce the extent of this whilst in space.

Loss of cognitive function The atmosphere of the Earth provides a wealth of protection from the harmful radiation of the sun. In missions outside the Earth’s orbit, radiation from space can pose a significant risk to astronauts. Radiation of course is known to be a cause of cancer but it can also lead to degenerative diseases and a loss of cognitive function- this is a particular problem as astronauts are required to carry out many complex tasks whilst on missions. Evidence for the degenerate and cognitive issues is provided through NASA funded studies in mice.


Unlike on earth, where the day/night cycle regulates our circadian rhythm and helps maintain a healthy sleeping pattern, in space this cycle can be irregular or not exist at all.

During this normal earth cycle, hormones are produced that may be wake-promoting or sleep-promoting and this can be altered due to exposure to the different wavelengths the sun emits.

However compare this to the different situations experienced by astronauts, for example in low Earth orbit, the sun rises and sets in a 90 minute cycle, meaning daylight is just 45 minutes. In some areas such as near mars, the wavelengths during daylight hours represent a red/brown colour which will also alter the hormones, and confuse the body more. As a result most astronauts have to rely on sleeping tablets or have to become accustomed to a new body clock before launch.

So, with all these changes to your body, would you still want to go into space?

#EmmaBrudenell #LaraMonkiewicz #Space #Health #Biology

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