struvite stones (ammonium magnesium phosphate), with the CAOX type being the most
common. Astronauts are at an increased risk for developing calcium oxalate, calcium
phosphate, and uric acid stones during space missions when crew’s urine typically becomes
supersaturated with the chemical species of
these stone-forming salts as a result of
decreased urine output and pH. Potassium
citrate is known to bind with calcium to impede
the growth of calcium-containing crystals, which
can become kidney stones. The Renal Stone
study quantifies the effectiveness of K-Cit in
lowering the elevated risk factors for renal stone
formation during space missions, and shows
significant decrease in CAOX and uric-acid
superstaturation risks in crew members
ingesting K-Cit versus the control groups. K-Cit
also increases urinary pH without elevating the
risk for forming brushite stones, and appears to
be well tolerated over the entire course of the
study. Results from this investigation suggest that supplementation with potassium citrate may
decrease the risk of renal stone formation during and immediately after space exploration
missions. Renal stones can be extremely debilitating and medical therapy options, widely
available on Earth, are severely limited during long-duration space exploration, hence
prevention is the most logical and cost-effective approach. The Renal Stone study, while
collecting valuable scientific data, stresses the importance of maintaining a balance between
pharmacological safety and effectiveness in conducting medical research involving crew
members. Related results are expected from an ISS investigation in progress with
bisphosphonates for mitigating bone loss, and a bed rest clinical ground study prescribing
magnesium potassium citrate (MKCIT) for reducing the risk of renal stone formation (Whitson
2009).
PUBLICATION(S)
Smith SM, Heer MA, Shackelford LC, et al. Bone metabolism and renal stone risk during
International Space Station missions. Bone. October 8, 2015;81:712-720. doi:
10.1016/j.bone.2015.10.002.
Whitson PA, Pietrzyk RA, Jones JA, Nelman-Gonzalez MA, Hudson EK, Sams CF. Effect of
potassium citrate therapy on the risk of renal stone formation during spaceflight. Journal of
Urology. 2009;182:2490-2496. doi: 10.1016/j.juro.2009.07.010.
This investigation is complete and all results are published.
The micrograph shows calcium oxalate crystals
in urine. These small crystals can develop to
form renal stones. NASA’s Marshall Space
Flight Center image.