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FINDING ways to prevent astronauts getting kidney stones could be crucial to
the success of long space flights such as missions to Mars. Studies on crews
from the Mir space station show that they are much more likely to get kidney
stones.

The stones can form without causing any pain. 鈥淏ut once renal stones start to
move they can be excruciatingly painful,鈥� says Peggy Whitson, an astronaut and
biochemist at the NASA Johnson Space Center in Houston. 鈥淵ou鈥檇 have an
incapacitated crew member and potentially have to abort the mission.鈥�

Earlier studies on short space shuttle flights up to 18 days long suggested
that there was an increased risk. 鈥淲e have had stones formed in crew members
after flight,鈥� says Whitson. To determine the risk during long space flights,
Whitson and her team took urine samples before, during and after Mir missions
lasting over 100 days between 1995 and 1999.

They found that crew members鈥� fluid intake and urine volume were
significantly lower than normal. Concentrations of calcium phosphate in urine
increased significantly, a condition that makes calcium salts more likely to
crystallise and grow into stones. Levels returned to around normal after a
month, but by this time stones could already have formed.

The loss of bone mass that occurs in microgravity is one cause. 鈥淒uring space
flight, crew members lose bone density. And the calcium that鈥檚 released ends up
in the urine. The higher urinary calcium levels are probably contributing to the
increased calcium stone-forming potential,鈥� says Whitson.

Joseph Zerwekh of Southwestern Medical Center at the University of Texas in
Dallas agrees. Losing calcium will increase the risk of a crew member getting a
fracture, but they might get kidney stones long before that, he says.

Kidney stones can usually be passed without surgery, though the process is
painful. Drinking lots of water helps both to pass stones and to prevent them
forming, but it means more urinating鈥攁 difficult proposition in space.
鈥淯rinating in toilets in orbit is time consuming, crew members are very busy,
and if they do extravehicular activity they don鈥檛 have the option,鈥� says
Whitson. Vomiting due to motion sickness can lead to further loss of fluid.

Potassium magnesium citrate supplements could be a more practical solution.
Citrate inhibits stone formation, and other studies have found that crew members
have low citrate levels in their urine. 鈥淥ne of our principal sources of citrate
is fresh fruit. And that is something you don鈥檛 find in space,鈥� says Zerwekh.

In a separate trial of 60 patients, supplements reduced their risk of kidney
stones by about 85 per cent, says Zerwekh. His team is testing the treatment on
volunteers on extended bed rest to simulate microgravity. Whitson鈥檚 team is
carrying out a similar study of potassium citrate on crew members living on the
International Space Station.