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“Alarming” bone deterioration after long space flights

Jan. 27, 2009
Courtesy Uni­ver­s­ity of Cal­i­for­nia Ir­vine
and World Science staff

As­tro­nauts spend­ing months in space lose sig­nif­i­cant bone strength, put­ting them at grow­ing risk for frac­tures lat­er in life, a study has found.

“If pre­ven­tive meas­ures are not tak­en, some of our as­tro­nauts may be at in­creased risk for age-related frac­tures dec­ades af­ter their mis­sions,” said study lead­er Joyce Keyak of the Uni­ver­s­ity of Cal­i­for­nia Ir­vine.

The Internation­al Space Sta­tion, a joint pr­oject of sev­eral na­tion­al space agen­cies, in an un­dated NA­SA photo. As­tro­nauts spend­ing months in space lose sig­nif­i­cant bone strength, put­ting them at grow­ing risk for frac­tures lat­er in life, a study has found.
Keyak and col­leagues eval­u­at­ed 13 as­tro­nauts who spent four to six months on the In­terna­t­ional Space Sta­t­ion. As­tro­nauts’ hip­bone strength dropped 14 per­cent on av­er­age, the sci­en­tists found; three space work­ers suf­fered losses of 20 to 30 per­cent, rates com­pa­ra­ble to those seen in old­er wom­en with os­te­o­por­osis. 

The re­search­ers said they were alarmed be­cause the re­sults re­vealed more se­vere bone de­te­riora­t­ion than pre­vi­ously meas­ured us­ing less pow­er­ful tech­nolo­gies. 

For years, re­search­ers have stud­ied why pro­longed time spent in out­er space leaves bones more frag­ile. In gen­er­al, it’s thought to oc­cur be­cause in the ab­sence of gra­vity, the bones no long­er do their reg­u­lar work of sup­port­ing body weight. The bones then stop main­tain­ing them­selves prop­er­ly.

Keyak and col­leagues used a com­put­er pro­gram she had de­vel­oped to iden­ti­fy hip­bone frac­ture risk in os­te­o­por­osis pa­tients, who suffer bone weak­en­ing as part of ag­ing. The re­search­ers used the pro­gram to an­a­lyze hip­bone scans of one fe­male and 12 male In­terna­t­ional Space Cen­ter crewmem­bers.

The de­crease in bone strength meas­ured be­tween 0.6 per­cent and 5.0 per­cent for each month of serv­ice on the sta­t­ion, Keyak said. That was no­ticeably great­er than monthly re­duc­tions in bone min­er­al dens­ity of 0.4 per­cent to 1.8 per­cent ob­served in pre­vi­ous stud­ies on the same sub­jects.

Or­tho­pe­dic re­search­ers look­ing in­to the ef­fects of long-dura­t­ion space­flight usu­ally study the hip­bone or spine. The hip suffers the great­est rate of bone loss in space, and a hip frac­ture al­most al­ways re­quires hos­pi­tal­iz­a­tion and ma­jor sur­gery. It can im­pair walk­ing abil­ity and may cause pro­longed or per­ma­nent dis­abil­ity or even death. The study re­sults ap­pear in the on­line ver­sion of the re­search jour­nal Bone.

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Astronauts spending months in space lose significant bone strength, putting them at growing risk for fractures later in life, a study has found. “If preventive measures are not taken, some of our astronauts may be at increased risk for age-related fractures decades after their missions,” said study leader Joyce Keyak of the University of California Irvine. Keyak and colleagues evaluated 13 astronauts who spent four to six months on the International Space Station. Astronauts’ hipbone strength dropped 14 percent on average, the scientists found; three space workers suffered losses of 20 percent to 30 percent, rates comparable to those seen in older women with osteoporosis. The researchers said they were alarmed because the results revealed more severe bone deterioration than previously measured using less powerful technologies. For years, researchers have studied why prolonged time spent in outer space leaves bones more fragile. In general, it’s thought to occur because in the absence of gravity, the bones no longer do their regular work of supporting body weight. The bones then stop maintaining themselves properly. Keyak and colleagues used a computer program she had developed to identify hipbone fracture risk in osteoporosis patients. The researchers used the program to analyze hipbone scans of one female and 12 male International Space Center crewmembers. The decrease in bone strength measured between 0.6 percent and 5.0 percent for each month of service on the station, Keyak said, which was noticeably greater than monthly reductions in bone mineral density of 0.4 percent to 1.8 percent observed in previous studies on the same subjects. Orthopedic researchers looking into the effects of long-duration spaceflight usually study the hipbone or spine. The hip experiences the greatest rate of bone loss in space, and a hip fracture almost always requires hospitalization and major surgery. It can impair a person’s ability to walk unassisted and may cause prolonged or permanent disability or even death. The study results appear in the online version of the research journal Bone.