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Muscle atrophy - In the microgravity environment of space, muscles do not need to support the body’s weight in the way that they do on Earth. If you were to travel to space, you would find your muscle fibers weakening due to muscle atrophy. All astronauts are subject to rigorous exercise regimes to mitigate these effects.

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Bone density loss -

Astronauts experience significant bone density loss due to the lack of gravitational forces in space. The bones lose minerals and become weaker and more susceptible to fractures, which poses serious long-term health risks upon return to Earth.

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Fluid redistribution -

In microgravity, bodily fluids shift upwards towards the head, which causes puffiness in the face, nasal congestion, and increased intracranial pressure.

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Peripheral edema -

The head isn’t the only place where fluid goes. While in space, bodily fluid flows to other extremities like the hands and feet, causing them to swell. This condition is known as peripheral edema, and can be truly uncomfortable.

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Cardiovascular deconditioning -

The heart and blood vessels also undergo changes in space. If regular exercise is not maintained, the heart may shrink, and the efficiency of blood circulation can decrease, leading to potential cardiovascular problems.

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Red blood cells -

Spaceflight can cause changes in red blood cell production and function, leading to conditions such as space anemia. This can result in fatigue and reduced oxygen in the blood, although this is rare.

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Radiation exposure -

Space travel exposes astronauts to higher levels of cosmic radiation than on Earth, since our atmosphere protects us from this. Higher radiation increases the risk of cancer and acute radiation syndrome.

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Psychological stress -

Isolation, confinement, and the absence of natural environmental cues can lead astronauts to experience psychological stress, anxiety, and depression. Astronauts are usually subjected to strict psychological evaluations to ensure they are good to go.

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Sleep disruption -

The absence of a natural day-night cycle in space can disrupt the body’s circadian rhythms, leading to sleep disorders. Poor sleep quality affects cognitive function and overall health, making it essential for astronauts to manage sleep patterns carefully.

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Immune system suppression -

Spaceflight has been shown to alter the human body’s immune function, making astronauts more susceptible to infections and diseases. The stress of space travel can further exacerbate these immune system changes and pose a significant health challenge.

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Immune system reactivation -

Interestingly, spaceflight can also reactivate dormant viruses in the body (such as the herpes virus) due to changes in the immune system. If treatment measures aren’t put in place, this reactivation can lead to outbreaks of conditions like shingles.

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Vision changes -

Long-duration spaceflight can cause changes in vision, often referred to as spaceflight-associated neuro-ocular syndrome (SANS). This includes swelling of the optic disc, changes in the retina, and also degradation of visual acuity.

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Vestibular system adaptations -

The human vestibular system, which helps maintain balance and spatial orientation, is extremely disrupted in microgravity, which can result in space motion sickness and impair an astronaut’s balance and orientation, especially upon reentry to Earth’s gravity.

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Nutritional challenges -

Maintaining proper nutrition in space is challenging due to altered taste perception and appetite changes. Even space food offers limitations, since it typically comes in flash-frozen packages.

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Dental health issues -

The unique conditions of space can even impact dental health. Changes in saliva production, diet, and oral hygiene routines can increase the risk of dental problems, which means that astronauts must maintain proper dental care and preventive measures in space.

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Skin conditions -

Due to the space environment’s impact on skin physiology, astronauts sometimes experience various skin issues, such as dryness and rashes. Proper skincare routines are important to manage these conditions.

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Microbial changes -

The confined environment of a spacecraft can alter the microbiome of both astronauts and their surroundings. This change can increase the risk of infections and impact overall health, which means that there are stringent protocols on spacecraft to ensure proper hygiene.

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Cognitive performance -

Spaceflight can have a minor effect on cognitive function, including memory and attention. Factors such as stress, sleep disruption, and radiation exposure can contribute to cognitive decline and have a drastic impact on a mission’s success.

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Decompression sickness - Astronauts may face the risk of decompression sickness–which can cause neurological issues–during spacewalks due to changes in atmospheric pressure between the outside and inside of the spacecraft. Space agencies have put proper protocols in place to prevent this.

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Kidney stones -

The body experiences many alterations in space that include fluid shifts and changes in calcium metabolism. These alterations can increase the risk of developing kidney stones, although a strict diet and hydration can mitigate it.

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Weight loss -

Space missions often result in a loss of body mass due to changes in metabolism and diet, not to mention the lack of gravity that causes muscle to weaken.

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Reproductive health -

The effects of spaceflight on reproductive health are not fully understood, but there is concern about potential impacts on fertility and reproductive function due to radiation exposure and other factors.

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Hearing loss -

Sometimes, it isn’t microgravity that causes health issues for astronauts. The increased noise levels within a space craft can lead to hearing loss if a person is exposed to it for a prolonged period.

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Gastrointestinal issues -

Microgravity can have a large effect on the digestive system. Some astronauts have been known to experience indigestion and even constipation while in space.

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Decreased lung function -

Changes in gravity can also have an effect on the body’s respiratory mechanics, which is why spacecraft is generically equipped with state-of-the-art air quality control systems.

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Spinal elongation -

In microgravity, the spine stretches due to the lack of gravity, and astronauts experience an increase in height. If the human body is subjected to microgravity for extended periods, it may experience back pain and spinal issues.

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Hydration -

Maintaining proper hydration in space is challenging due to the difficulty of drinking in microgravity. Dehydration can cause significant health problems, so adequate fluid intake is essential.

Sources: (National Geographic) (Space.com) (NASA) (Astronomy Magazine)

See also: Astronauts who have been in space the longest

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