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Spaceflight osteopenia refers to the characteristic bone loss that occurs during spaceflight. Astronauts lose an average of more than 1% bone mass per month spent in space.

Risk Of Early Onset Osteoporosis Due To Spaceflight

Osteoporosis results from gradual loss of bone density, so that the skeleton becomes weaker and more susceptible to fractures. Like patients with osteoporosis, astronauts who spend longer periods of time in space also experience bone loss, but at a much faster rate.

They typically experience bone loss in the lower halves of their bodies, particularly in the vertebrae (spine) and the leg bones. The proximal femoral bone (thigh bone) loses 1.5 percent of its mass per month, or roughly 10 percent over a six-month stay in space, with the recovery after returning to

Earth taking at least three or four years.

Currently, the measurement of areal bone mineral density (aBMD) is used at NASA to evaluate the effects of spaceflight on the skeletal health of astronauts.

Notably, there are precipitous declines in aBMD with losses >10 % detected

in the hip and spine in some astronauts following a typical 6-month mission in space. How those percentage changes in aBMD relate to fracture risk in the younger-aged astronaut is unknown.

Risk factors that could be contributing to this bone loss

An astronaut performing exercise in the International Space Station. Credits: JAXA/NASA

Reduced physical activity

ư- Gravity


Adaptation to weightlessness

Perturbed mineral metabolism

Suboptimal diet

There is concern that during long duration flights, excessive bone loss and the associated increase in serum calcium ion levels will interfere with execution of mission tasks and result in irreversible skeletal damage.

Conflicts of interests

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None stated by the authors.

After a 3—4 month trip into space, it takes about 2–3 years to regain lost bone density.

Department of Physiological Sciences - Grupo de Investigación en Salud (GIS) No -02INFORMATION CIRCULAR: Spaceflight and osteoporosis.

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1-Jhan Sebastián Saavedra-Torres 2-Luisa Fernanda Zúñiga-Cerón 3-Luisa Fernanda Mahecha Virgüez 4-Alicia Andrea Ortega Narváez 5-María Virginia Pinzón Fernández 6-Nelson Adolfo López Garzón

Credits: NASA

Astronauts take bisphosphonate once a week to prevent bone loss in space. Credits: JAXA/NASA

Recommended Reading: NASA (Laurie J. Abadie, Charles W. Lloyd, Mark J. Shelhamer, NASA Human Research Program) - see link:

Conflicts of interests

None stated by the authors


None stated by the authors.


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Consult reports and evidence of human research of NASA "Human Research Roadmap":

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