[ RadSafe ] Radiation and Bone Loss

[Mercado, Don]

>From http://space.com/scienceastronomy/060718_radiation_bones.html
A single dose of radiation approaching what will be faced by long-term
space travelers to the Moon or Mars causes as much as a 39 percent
spongy bone loss in mice, a new study shows. 
The loss of connectivity in spongy bone ranged as high as 64 percent for
one of the types of radiation tested, along the lines of an osteoporosis
diagnosis.
The results say nothing directly about the effect of space radiation on
people but it has implications for the future of human spaceflight,
especially given the U.S. commitment to send astronauts on long trips
<http://www.space.com/news/bush_plan_faq_040115.html>  beyond low-Earth
orbit <http://www.space.com/spaceshuttle/index.html> . Both mice and
humans lose bone after radiation exposure. 
"We were surprised that there was bone loss, and the degree was a lot
more than we expected," said Ted Bateman of Clemson University, lead
author of the research report. "We're seeing bone loss at much lower
doses of radiation than we expected."
What's lost 
Scientists already know that cancer
<http://www.livescience.com/humanbiology/cancer_killer_050120.html>
patients who receive radiation treatments have a higher risk for
spontaneous bone fractures down the line. Now it's more clear why.
For Bateman's experiment, 38 female mice were exposed to radiation,
receiving about the same amount that would be a single day's dose for
someone suffering from cancer. The gamma, proton, carbon and iron
radiation used in the experiment is less damaging than the complex mix
of radiation (protons and heavy ions, or ionizing radiation) that
long-term space travelers will experience
<http://www.space.com/scienceastronomy/mars_dangers_040120.html> .
Bone is comprised of hard or cortical bone on the outside and marrow
inside, as well as bone adjacent the marrow, called trabecular bone.
This spongy part of the bone is key to bearing weight and preventing
fractures. In the experiment, radiation had no real effect on cortical
bone. 
The result of Bateman's study, published in Journal of Applied
Physiology, was a profound loss of trabecular bone-about 30 percent for
all types of radiation, with carbon radiation inflicting 39 percent
loss, the most of all. The loss of spongy connections in the four
radiation groups ranged from 46 to 64 percent, with proton radiation
inflicting the worst damage in terms of connectivity.
Fewer interconnected struts means more load on each of them, leaving
bone structure less efficient and more vulnerable to fracture. 
Trabecular bone connectivity is irreplaceable once lost. "You can regain
bone mass," Bateman told SPACE.com, "but once the connections between
struts is lost, the load is not being passed from strut to strut and
that becomes permanent. Struts can become larger and thicker but loads
are not transferred as efficiently once you've lost the connections
between struts."
Implications
Currently, astronauts on the International Space Station
<http://www.space.com/missionlaunches/060710_sts121_posteva2.html>  and
shuttle <http://www.space.com/spaceshuttle/index.html>  lose about 2
percent of their bone mass for each month in space as a result of
microgravity much more than as a result of cosmic or solar radiation
given their relatively short stays in space and protection by Earth's
magnetic field
<http://www.space.com/scienceastronomy/solar_storms_041215.html> . 
The new study shows that on longer flights, such as a 6-month trip to
the Moon <http://www.space.com/news/060214_staif_moonplans.html>  or
30-month trip to Mars
<http://www.space.com/news/bush_plan_faq_040115.html> , the bone lost as
a result of microgravity
<http://www.space.com/missionlaunches/bone_study_040315.html>  will be
compounded by more extensive bone loss as a result of radiation
exposure. Up to now, NASA has focused on radiation's cancer-causing
properties and effect on the central nervous and immune systems. The
effect on bone health has been unexamined. 
"Now we're concerned that radiation and reduced gravity are both going
to contribute to bone loss," Bateman said.
Procter and Gamble, which makes an osteoporosis drug called Actonel,
helped to support the research.


Donald P. Mercado
Radiation Safety Officer
Explosives Safety Officer
Lockheed Martin Space Systems Company
O/9K-2S, B/157
1111 Lockheed Martin Way
Sunnyvale, CA 94089
Ph. (408) 742-0759
Fx. (408) 756-0504
Don.Mercado at lmco.com
"Life is not a journey to the grave with the intention of 
arriving safely in a pretty and well preserved body, but 
rather to skid in broadside, thoroughly used up, totally 
worn out, and loudly proclaiming 
-- WOW!!! -- What a Ride!!!"