Prolonged space travel could affect kidneys

 From Behind the Black, a space blog:

an article from Univ College London quoting Nature points out problems with the heart, body and kidneys have been known for years.

But now there is a question if it comes from solar radiation rather than just low gravity. But no, it seems to be from low gravity:

The primary reason that kidney stones develop during space missions had previously been assumed to be solely due to microgravity-induced bone loss that leads to a build-up of calcium in the urine. Rather, the UCL team’s findings indicated that the way the kidneys process salts is fundamentally altered by space flight and likely a primary contributor to kidney stone formation. Perhaps the most alarming finding, at least for any astronaut considering a three-year round trip to Mars, is that the kidneys of mice exposed to radiation simulating GCR for 2.5 years experienced permanent damage and loss of function.