The Biggest Health Risks in Space


Since people began travelling in space in 1961, and Yuri Gagarin became the first human to orbit Earth, many people have been dreaming about travelling into orbit, to the Moon or even beyond. However, venturing into the environment of space can have negative effects on the human body. In the words of Star Trek’s legendary doctor Leonard “Bones” McCoy, “Space is disease and danger, wrapped in darkness and silence!” He has a point; space travel leaves you weak, tired, sick, and possibly, depressed.

Gravity in space is much weaker than it is on Earth; when people travel in space, they seem to become weightless. Following the advent of space stations that can be inhabited for long periods of time, exposure to weightlessness has been demonstrated to have some deleterious effects on human health. The most common problem experienced by humans in the initial hours of weightlessness is known as Space Adaptation Syndrome (SAS); commonly referred to as space sickness manifested by nausea and vomiting, vertigo, headaches, lethargy, and overall malaise. The first case of SAS was reported by cosmonaut Gherman Titov in 1961; since then, roughly 45% of all people who have flown in space have suffered from this condition. The duration of space sickness varies, but rarely has it lasted for more than 72 hours, after which the body adjusts to the new environment.

Significant adverse effects of long-term weightlessness include also muscle atrophy and deterioration of the skeleton. Without the effects of gravity, skeletal muscles are no longer required to maintain posture. In a weightless environment, astronauts put almost no weight on the back muscles or leg muscles used for standing up. Those muscles then start to weaken and eventually get smaller and atrophy rapidly. Though these changes are usually temporary, without regular exercise and a special diet, astronauts can lose up to 20% of their muscle mass in just 5–11 days.

One other effect of weightlessness on humans is that some astronauts report a change in their sense of taste when in space. Some astronauts find that their food is bland, others find that their favorite foods no longer taste as good; some astronauts enjoy eating certain foods that they would not normally eat, and some experience no change whatsoever. Multiple tests have not identified the cause; several theories have been suggested, including food degradation, and psychological changes such as boredom. Astronauts often choose strong-tasting food to combat the loss of taste.

The environment of space is lethal without appropriate protection. The greatest threat in the vacuum of space derives from the lack of oxygen and pressure, although temperature and radiation also pose risks. A certain amount of oxygen is required in the air we breathe; the minimum concentration, or partial pressure, of oxygen that can be tolerated is 0.16 bar. In the vacuum of space, gas exchange in the lungs continues as normal, but results in the removal of all gases, including oxygen, from the bloodstream. After 9–12 seconds, the deoxygenated blood reaches the brain, resulting in the loss of consciousness and possibly leading to hypoxia and death.

On the other hand, unprotected by the Earth’s atmosphere and magnetic field, astronauts are at greater risk from the high levels of radiation emitted by the Sun and by distant stars and galaxies. A year in Low-Earth Orbit results in a dose of radiation 10 times that of the annual dose on Earth. High levels of radiation damage lymphocytes—cells heavily involved in maintaining the immune system—which contributes to the lowered immunity experienced by astronauts. Radiation has also recently been linked to a higher incidence of cataracts in astronauts. Long periods of exposure to radiation can trigger cases of cancer, while even short-duration exposure to extremely high levels, such as that generated by solar flares, can cause potentially fatal radiation poisoning.

Astronauts sleep poorly in space. On some space shuttle missions up to 50% of the crew take sleeping pills, and over all nearly half of all medication used in orbit is intended to help astronauts sleep. Even so, space travelers’ average sleep hours each night in space are about 2 hours less than they do on the ground. Fatigue, on Earth or in space, is a serious problem; it affects performance, increases irritability, diminishes concentration, and decreases reaction time, thus increasing the risk of accidents as well. Scientists hope to help crews increase their alertness and reduce performance errors through improvements to spacecraft lighting, sleep schedules, and the scheduling of work shifts.

Those are just some of the effects a trip to space can have on the human body. Scientists and physicians are still working to enhance medical care in space and find solutions to the health challenges of living and working in space for long periods of time. The techniques addressing astronaut health risks on long missions will also benefit patients suffering from similar conditions on Earth; such as bone loss, muscle wasting, shift-related sleep disturbances, and balance disorders.


Top Image: Astronaut photo created by Rochak Shukla -

This article was first published in print in SCIplanet, Winter 2017 issue.

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