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Another study at the Medical College of Georgia is investigating
a possible connection between eating and bone destruction.
Ingestion of food causes levels of a certain hormone
-- called "glucose-dependent insulinotropic peptide"
-- to increase in the bloodstream. The main function
of this hormone is to stimulate the production of insulin
after a meal, which in turn triggers cells to absorb
energy-providing glucose from the blood.
Bone cells are sensitive to this hormone, too. Researchers
have found that when this hormone attaches to "receptor"
molecules on bone cells, osteoclast (bone destroying)
activity goes down and osteoblast (bone creating) activity
goes up.
Could hormones like this one be given to space travelers
as a supplement to prevent bone degradation? Scientists
don't yet know.
Genetic make-up might also play a role, as suggested
by the variation of bone loss observed between individual
astronauts and cosmonauts.
"The 1 to 2 percent per month loss is an estimate of
bone loss -- an average value," Shapiro says. "Certain
individuals on six month flights have lost as much as
20 percent of bone mass in their lower extremities,
while a few have lost none during the same period in
space."
"Bone loss of this magnitude leads to a significant
increase in fracture rate, which may be as much as five-fold
that expected with normal bone mass on Earth," he added.
"A limb fracture involving, say, one of a six-person
space crew could seriously compromise a mission's objectives."
Indeed, adds Shapiro, "the problem of bone loss must
be overcome before people are placed in the position
of performing physically hazardous tasks [after a long
voyage in zero-G]." Future astronauts who visit Mars,
for instance, will need strong healthy bones when they
step out of their spaceship and onto the Red Planet.
Humans won't be striding across Mars for some time,
but bone loss is hardly a far-off concern. Right here
on our own planet millions suffer from osteoporosis
-- a malady that strikes ordinary people and far-out
explorers alike. Solving the problem in space, say researchers,
will likely bring welcome relief back home to Earth.
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