In space, no one can hear you pee

By Phil Plait | June 27, 2006 10:48 pm

When the Shuttle lifts off on July 1, the astronauts on board may well be concerned about their safety. But now they have something else to worry about: kidney stones.

A University of Minnesota study revealed that astronauts may be at risk for developing kidney stones. The study simulated microgravity by having twins stay in bed for 30 days, except one of the twins exercised. The twin who didn’t tended to have higher levels of calcium in their urine, a precursor to stones.

I don’t have access to the Journal of Urology, unfortunately, where the study was published (this is, in fact, the first time I have been upset I don’t have access to the Journal of Urology). I’d like to read that article and see what’s what. It sounds interesting, honestly, since I sometimes wonder what we don’t know about long-term exposure to microgravity. We need to know this stuff before we go to Mars!

And I wonder… what will it do to the human body when people live on the Moon, in 1/6th gravity? Our bodies have evolved in one gravity, and may not work properly in lower gravity over long periods of time. What else don’t we know?

CATEGORIZED UNDER: Cool stuff, NASA, Science

Comments (25)

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  1. Space Shuttle Countdown -- | June 28, 2006
  1. I’ve had four, or is it five? kidney stones. They suck, but I imagine it’d a little more enjoyable in free fall.

    Just a little.

  2. I guess that’s another reason to push exercise for astronauts. But it’s interesting that this is directly tied into another big problem that astronauts face from long-duration flights, namely bone loss. My understanding is that the calcium from the bones displaces elsewhere in the body, which is what causes the kidney stone risk for astronauts. So solving the bone loss problem might also yield a solution for the kidney stone problem.

  3. One thing to expect out of any space travel is to live in a spinny thingy that approximates earth gravity.

    Any attempt at a moon honeymoon would most likely end up in pukeville….
    or kidneystoneville
    or osteoporosisville.

    Till date people think of space travel as an extension of humankinds exploration of earth.There is an implicit comparision to the explorers who ventured into the far corners of earth with the astronauts who venture outside our cosy little bubble called earth into the nothingness of space.

    Space travel is a long way away for the comman wo/man

  4. Mark Hansen

    Kidney stones in orbit would really ruin your day. Better make sure they carry ample supplies of seriously heavy-duty painkillers. The one I had, which curiously enough was kidney-shaped, was THE most painful thing I’ve ever felt.

  5. Dean

    Guess I’m kinda slow but how does laying in bed simulate microgravity? Sedentary lifestyle yes, but aren’t they still being acted on by Earth’s gravity?

  6. Irishman

    The intent is to not let them get vertical. Thus they don’t get regular gravity resistance in the vertical direction. No excercise on the legs, back, etc. Yes, basically it is sedentary lifestyle, but total bedrest. That is a partial condition of microgravity – reduced exercise on the muscles and bones. It can reproduce some of the health effects – the ones related to not exercising.

  7. Supernova

    Bleah, count me out of THAT study. (Good thing I don’t have an identical twin!) I wonder how the ones who exercised did so while lying down?

  8. Hawk

    Microgravity health studies are one of the many problems with long duration spaceflights, such as a Mars journey. We have a very limited sample set, astronauts, and a very limited set of things we can do to them. A Mars mission may extend 3 years, 2 years in zero G and one year at ~1/3 G. Does time at low G help you recover from the years at zero? Will our explorers be working with heart problems and bone loss? Hopefully a long duration lunar mission might help us discuss some of these problems.
    We are doing some tests on mice and human tissue, but frankly, mice and chimps (if they were even being used) do not have human health issues. We have less than a hundred man-years of human studies. When we have a thousand or so, we may have a grasp of the size of the problems.

  9. Ingrid

    Indeed! This is nothing new, we’ve known for years that without weight bearing exercise bone mass is difficult to maintain even with adequate calcium consumption. So of course in a weightless environment the calcium consumed/present is more likely to take the form of stones as opposed to bone mass.


  10. SLC

    Maybe you should listen to bob Park!

  11. Max Fagin

    I’ve never understood the need for micro gravity research before we go to Mars. We don’t need to fly to Mars in a zero gravity mode at all.

    Just spin the spacecraft.

    Put the landing vehicle at one end of a tether, and the spent final stage of the launch rocket at the other end. Let out 86 meters of tether; spin the system up to 2 rpm and voila! The crew experiences .38 G’s (Mars’ gravity) with negligible coriolis forces and gravity gradients, (and no kidney stones.)

    Would someone please explain to me why micro gravity is still on the list of showstoppers for a Mars mission?

  12. TheBlackCat

    According to my biomechanics textbook the rate of bone mass decrease during bed rest is approximately 1% per week. Monkeys immobilized in full-body casts for 60 days suffered a threefold decrease in load to failure in their vertabrae. And the changes are not compltely reversible. I don’t have that bit of info definitively, but I am pretty sure the professor said after just 6 weeks of having a limb immobilized in a cast irreversible changes in bone strength begin to set in, and progressively increase from that point.

  13. Shawn S.

    There have been a number of interesting scenarios posited on this subject by science fiction authors. The one that stands out most to me is Fritz Leiber’s “A Specter is Haunting Texas.” The main character, in a very twisted fish-out-of-water story, is from the colony on the moon (recently independent and communist) who comes to earth. He has to use a motorized exoskeleton to support himself in Earth’s gravity, and copes with a number of health issues while on his little adventure. A Heinlein novel mentions a sort of ‘no turning back’ point for anyone living in microgravity. A character who has to go to earth dies from heart failure because his body is not used to the strain that Earth puts on it. Fiction, of course, but worth reading.

    Did you check pubmed for the Journal article?

  14. Woof

    Nah, kidney stones are no big deal. I have a collection of them at home.

    They’re a pain in the back while hung up between kidney and bladder, but passing them is easy: You’re letting it flow, the stone falls into the pipe (OK, “falls” could be a problem in microgravity, but I imagine it’ll get there eventually), it rips at the walls of the pipe with its sandpaper-like surface as it passes through, you suck ALL THE ROOM AIR into your lungs, there’s a *tink* sound as it hits the porcelain (modify if you’re using a space-based baggy), then… all is OK.

  15. Max: Microgravity is still a problem for Mars missions basically because artificial gravity is not as easy as you say. H

    ow do you spin your assembly to 2 rpm? This is not trivial! If you just spit out some thrust from your hab capsule, your structure is going to have an undesired translation as well as the rotation effect you want. And since the tether is of course non-rigid, firing thrusters from the counterweight won’t necessarily work because you can’t really guarantee it being oriented correctly. And then you still have to re-spin it every once in a while, as torque effects are going to cause you to lose angular momentum slowly through the duration of the flight (not to mention throw your ship off course!)

    Oh, and then there’s the fact you’re dragging a dead weight equal in mass to the entire rest of your spacecraft, which means you have to pack on twice as much fuel. Except really you’re bringing MORE than twice as much fuel, since you have to be able to transport the extra fuel you just packed on to move around your big old dead weight.

    It’s simply not feasible like you say.

  16. Max Fagin


    Getting the spin rate up to 2 rpm isn’t that hard, you don’t need thrusters on the spent upper stage. You can achieve 2 rpm by using thrusters on the habitat. It doesn’t push the spacecraft off course either. The delta V for Mars missions would be around 30 km/sec; the small push needed to start spinning can be easily corrected for later in the mission. After all, interplanetary probes like Cassini were spinning, and JPL was able to maneuver them using short, repeated, timed burns.
    You don’t need to bring along more propellant either. Just like with the Apollo missions, the final stage is what sends the astronauts on their trans-lunar/Martian trajectory. The final stage comes along for the ride anyway, so why not use it?

  17. Nigel Depledge

    An alternative way of generating the required centrifugal force* might be to have your craft with two sections that can spin in opposite directions. It does add the problem of moving from a chamber spinning one way into a chamber spinning the other way, but I daresay humans are sufficiently adaptable to cope with that. It might also give larger force gradients, but I am sure there are ways to work around this.

    *OK, please don’t tell me there’s no such thing as centrifugal force. I use centrifuges at work, and the densest bits of the mixture invariably end up at the bottom of the centrifuge pots after a spin. Something makes that happen.

  18. Nigel Depledge

    D’oh, I meant to add that having two sections spinning in opposite directions neutralises any impact on your trajectory.

  19. There has never been a kidney stone incident in space! That being said, the composition of the urine in space shows a profile that would predispose someone to kidney stones. For example, more acid urine, uric acid, and a greater amount of oxalates and other salts are considered risk factors. Any condition that results in dehydration and therefore concentrated urine is a strong risk factor and this includes distance runners as well as astronauts. In those that exercise because of sweating and not drinking enough to replace lost water, kidney stones are common. In the case of astronauts in space the risk factor increases but because they live in minimal gravity. This has been known a long time, and precautions have been taken to reduce the risk. In fact, one of the first research studies done on ISS by Peggy Whitson, Potassium Citrate was tested for its ability to make urine more alkaline and therefore reduce the kidney stone risk; and it does.
    Minimal gravity does not increase kidney stone risk because of inactivity but because the body’s first response to getting away from gravity is to dump what it reads as excess water, by peeing. Why? Because on first going into space gravity is no longer pulling blood to the feet so it rushes upward to the head and chest. Sensors in the neck and chest register this as increased volume and trigger the peeing response. What results is a 10-15% reduction in blood volume which the sensors consider appropriate for a human who lives in microgravity.
    Gravity on Earth pulls in one direction only — downward. When you stand it pulls your mass and the liquid in your body including blood to your feet. Standing, you experience what we call 1G. It is your heart and blood vessels that have to pump and work hard to get the blood back up to your head otherwise you will pass out, black out or faint. That is why we use bed rest — lying in bed continuously — as the closest, practical simulation model to being in microgravity. When you lie down gravity is no longer pulling on you from head to toe but its influence is minimized because it is only pulling across your chest. Lying in bed continuously is something like living in space…without the view! It produces most of the changes we see in returning astronauts and in space except they take longer to develop and are not as intense.
    The study with the twins in the Journal of Urology used bed rest for this purpose. Bed rest has been a very valuable simulation model since it has been possible to study in many more healthy volunteers than available astronauts and more thoroughly, what happens to the human body in space, why and how to prevent adverse changes with the best countermeasures. Only promising results from these studies can then be validated in the precious few opportunities available today for science in space.

    Drinking more water in space, unlike in athletes, does not necessarily help to restore the lost fluid. Astronauts are encouraged to drink to maintain good flow of water through the kidneys but unlike in athletes on Earth, it is not retained and exercise in space does not correct the problem. Increased gravity such as by standing on Earth or in space, by some other means, does.
    In the Urology paper the investigators tested during bed rest a countermeasure device that uses Lower Body Negative Pressure (LBNP)which by applying vacuum sucks blood down to the feet to a level equivalent to what would happen if the volunteers stood up and experienced 1G. As far as the heart and circulation are concerned this triggers the normal response to standing and is similar to being upright on the ground. They added exercise, because calcium loss may be reduced in bed by some types of exercise. The primary benefit of this countermeasure for reducing kidney stones does not come from the exercise but the body loading provided by the gravity-like effect of the LBNP.
    How come you all did not know about this and other effects of space flight? Because NASA would get the Award for their inability of communicating science to the public.

  20. Don L.

    If William Shatner can sell a kidney stone for $25,000, then maybe NASA can sell astronaut kidney stones to help fund the space program.

  21. Tim G

    This reminds me of a poster I saw about twenty years ago.

    It depicted a suited-up astronaut on the moon. Apparently, the suit had a fly because he was taking a wiz that produced an arc that spanned fifty feet.

  22. Brian

    I wouldn’t be so concerned about the effects of microgravity. Phil mentions that we ‘evolved’ in Earth’s gravity. WRONG! We were intelligently designed to survive in Earth’s gravity and there is no reason to doubt that the infallible designer had the foresight to know we would one day explore space!

    Unless perhaps my momma was wrong when she tried to teach me 12th grade level biology during my homeschooling years…. Nah.

  23. Gary Ansorge

    Joshua: I take it you are unfamiliar with magnetic bearings? Torque transfers thru friction!

    Counter rotating masses? Sounds good to me.

    I still think building in orbit power sats is the way to go, before trying for MArs. Besides, planets are sucky places, or is that just gravity???

    Gary 7

  24. Irishman

    Woof said:

    Nah, kidney stones are no big deal. I have a collection of them at home.

    They’re a pain in the back while hung up between kidney and bladder, but passing them is easy: You’re letting it flow, the stone falls into the pipe (OK, “falls” could be a problem in microgravity, but I imagine it’ll get there eventually), it rips at the walls of the pipe with its sandpaper-like surface as it passes through, you suck ALL THE ROOM AIR into your lungs, there’s a *tink* sound as it hits the porcelain (modify if you’re using a space-based baggy), then… all is OK.

    That works fine until you get that kidney stone that is a bit bigger than the pathway out. They you plug the plumbing, and not only get that stabbing back pain, but that it keeps building and won’t go away, and you need surgery to remove. Or orthoscopic technique up your catheter.


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