Spaceflight osteopenia refers to the characteristic bone loss

Bone loss

Bone loss may refer to a number of entities:* Osteoporosis, a condition in which overall bone density decreases* Periodontitis, a condition in which the supporting bone around teeth exhibits resorption...

 that occurs during spaceflight

Spaceflight

Spaceflight is the act of travelling into or through outer space. Spaceflight can occur with spacecraft which may, or may not, have humans on board. Examples of human spaceflight include the Russian Soyuz program, the U.S. Space shuttle program, as well as the ongoing International Space Station...

. Astronaut

Astronaut

An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....

s lose an average of more than 1% bone mass per month spent in space

Outer space

Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

. There is concern that during long duration flights, excessive bone loss and the associated increase in serum calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 ion levels will interfere with execution of mission tasks and result in irreversible skeletal damage.

History

Bone loss has been noticed at least as early as Gemini

Project Gemini

Project Gemini was the second human spaceflight program of NASA, the civilian space agency of the United States government. Project Gemini was conducted between projects Mercury and Apollo, with ten manned flights occurring in 1965 and 1966....

. Although most early measurements of the amount of bone loss were not reliable, they did show bone loss in Gemini, Soyuz 9

Soyuz 9

Soyuz 9 was a 1970 Soviet manned space flight. The two-man crew of Andrian Nikolayev and Vitali Sevastyanov broke the five-year-old space endurance record with their nearly 18-day flight...

, Apollo, Skylab

Skylab

Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...

, Salyut 7

Salyut 7

Salyut 7 was a space station in low Earth orbit from April 1982 to February 1991. It was first manned in May 1982 with two crew via Soyuz T-5, and last visited in June 1986, by Soyuz T-15. Various crew and modules were used over its lifetime, including a total of 12 manned and 15 unmanned launches...

, Mir

Mir

Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...

, and the International Space Station

International Space Station

The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

. William E. Thornton

William E. Thornton

William Edgar Thornton is a former NASA Astronaut. Thornton was born in Faison, North Carolina, and is married with two sons to the former Elizabeth Jennifer Fowler of Hertfordshire, England.-Education:...

, an astronaut and physician, was one of the biggest proponents of exercise as a way of preventing bone loss.

Countermeasures

Since Gemini, exercise has been tried as a way of preventing bone loss, but it has not been shown to be successful. This may be in part due to lack of adequately designed studies (no controlled study had been done as of 2005, either in space or using bedrest as an attempt to simulate conditions which lead to bone loss). It is not known whether a different exercise regimen (perhaps including larger loads than past ones) would be effective.

Increasing dietary calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 and vitamin D

Vitamin D

Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 is a standard countermeasure for osteoporosis

Osteoporosis

Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...

.

A variety of drug remedies currently used or proposed for osteoporosis may work for spaceflight, including hormone therapy

Hormone replacement therapy (menopause)

Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...

 (estrogen and/or progestin), selective estrogen receptor modulator

Selective estrogen receptor modulator

Selective Estrogen Receptor Modulators are a class of compounds that act on the estrogen receptor. A characteristic that distinguishes these substances from pure receptor agonists and antagonists is that their action is different in various tissues, thereby granting the possibility to selectively...

s, bisphosphonate

Bisphosphonate

Bisphosphonates are a class of drugs that prevent the loss of bone mass, used to treat osteoporosis and similar diseases...

s, teriparatide

Teriparatide

Teriparatide is a recombinant form of parathyroid hormone, used in the treatment of some forms of osteoporosis. It is manufactured and marketed by Eli Lilly and Company.-Administration:...

, and others. Whether they can provide the same benefits for spaceflight as they do for osteoporosis is not yet known.

See also

• Artificial gravity
  Artificial gravity
  Artificial gravity is the varying of apparent gravity via artificial means, particularly in space, but also on the Earth...
  
  
• Human adaptation to space
  Human adaptation to space
  Human physiological adaptation to the conditions of space is a challenge faced in the development of human spaceflight.The fundamental engineering problems of escaping Earth's gravity well and developing systems for in-space propulsion have been examined for well over a century, and millions of...
  
  
  • Space medicine
    Space medicine
    Space medicine is the practice of medicine on astronauts in outer space whereas astronautical hygiene is the application of science and technology to the prevention or control of exposure to the hazards that may cause astronaut ill health. Both these sciences work together to ensure that...
    
    
  • Space adaptation syndrome
    Space adaptation syndrome
    Space adaptation syndrome or space sickness is a condition experienced by around half of space travelers during adaptation to weightlessness. It is related to motion sickness, as the vestibular system adapts to weightlessness.- Cause and remedy :...
    
    
• Microgravity University
  Microgravity University
  Microgravity University, also known as the Reduced Gravity Student Flight Opportunities Program is a program run by NASA which enables undergraduate university students to perform microgravity experiments aboard NASA's DC-9 aircraft at Johnson Space Center in Houston, Texas.Acceptance into the...
  
  
• Vomit Comet
  Vomit Comet
  A Reduced Gravity Aircraft is a type of fixed-wing aircraft that briefly provides a nearly weightless environment in which to train astronauts, conduct research and film motion pictures....