![]() Weightlessness has a profound impact on macrophage metabolism, growth and reproduction, as well as the modes of communication between macrophages and the rest of the body's immune system, the review authors wrote. Prolonged exposure to microgravity can reduce the number and function of macrophages, a type of white blood cell that kills harmful microbes and regulates the action of other immune system cells, according to a 2021 review published in the journal npj Microgravity. The cosmic radiation, microgravity and overall physical and mental stress involved in space travel can weaken astronauts' immune systems and thus make them more susceptible to infections and systemic diseases. In microgravity, however, this daily fluctuation is lost, the review authors wrote. This turnover allows the disc to maintain optimal levels of hydration and thus preserve its structure and functionality. During sleep, in a horizontal position, the gravity load is lost and the discs can rehydrate. Under normal gravity conditions, the spine is compressed, which causes the discs to expel water throughout the day. Intervertebral disc degeneration in space appears to be caused by water loss. In addition, weightlessness may lead to the degeneration of their intervertebral discs, the shock-absorbing cushions located in between vertebrae, according to a 2023 review published in the journal Frontiers in Physiology. However, prolonged stints in microgravity may weaken muscles that support their vertebrae. The human spine is flexible, so short space missions are unlikely to cause lasting damage. In fact, astronauts can "grow" up to three inches (7.6 centimeters) in a weightless environment, according to NASA. In microgravity, the spinal column elongates and somewhat straightens. The culprit driving this pain is microgravity and its profound effect on the human spine.Įarth's gravity keeps the spinal column compressed and in its typical, slightly curved shape. Back painĪstronauts often complain of back pain after returning home from long-haul space flights. Prolonged exposure to microgravity can also lead to a degenerative condition called Spaceflight Associated Neuro-ocular Syndrome (SANS), the symptoms of which include flattening of the eyeball, white lesions on the eye's innermost layer known as "cotton wool spots," and other tissue damage to various parts of the eye. ![]() They found that long periods in microgravity lead to a significant change in the accuracy and speed of eye rotations, which in turn may impair the astronauts' ability to visually track objects, the study authors wrote. Researchers examined astronauts who took part in long-haul missions on the International Space Station, before and after their flights. In microgravity, these eye movements may be disrupted, according to a 2006 study published in the journal Human Physiology. Gravitational forces help keep the eyeballs in their correct positions and allow them to swivel in the eye sockets, according to a 2009 review published in the journal Annals of the New York Academy of Sciences. Vision is also affected by several factors including Earth's gravity. ![]() For example, the nerves that extend from the back of the eye may change in microgravity and then warp upon being returned to Earth gravity. Vision problemsĮyes are undoubtedly some of the most delicate and complex organs in the human body, so it comes as no surprise that going into space can have a damaging effect on our eyes and sense of vision. In space, there is no force pulling the body and its internal fluids down towards the Earth, which in turn may affect the distribution of factors that control the formation of bone tissue, the meta-analysis authors noted.Īs bone tissue rapidly degrades in space, it can releases a flood of minerals into the blood, elevating the risk of hypercalcemia (excessive levels of calcium), which in turn can cause kidney stones, according to a 1995 review published in the journal Acta Astronautica. Bones in the lower limbs and the lumbar spine may lose up to 1% of mass per month a person spends in space, while the density of the skull bones can actually increase, according to a 2020 meta-analysis published in the journal npj Microgravity. Interestingly, microgravity's effects on specific bones may depend on their location in the body. Astronauts can suffer decades' worth of bone loss after spending six or more months in space, which makes them more prone to bone fractures and osteoporosis. The human skeleton also relies on weight-bearing exercises to maintain its mass and density.
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