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Thread: pee or hold it in to stay warm?

  1. #1 pee or hold it in to stay warm? 
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    Howdy- a mate of mine has this theory that if you're out camping in the cold, it's better to pee as soon as you get the urge, so you are no longer using energy to keep that 200ml of liquid at body temperature. When he told me this, i said that i reckon it's better to hold it, because the liquid is already at body temperature, so you are losing that heat energy when you pee and also by peeing you are reducing your mass to surface area ratio (i.e a skinnier person gets colder faster than a fat person). all other things being equal (i.e you're not drinking anything)- who is right, and for what reason?


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  3. #2 Re: pee or hold it in to stay warm? 
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    Quote Originally Posted by rowan
    Howdy- a mate of mine has this theory that if you're out camping in the cold, it's better to pee as soon as you get the urge, so you are no longer using energy to keep that 200ml of liquid at body temperature. When he told me this, i said that i reckon it's better to hold it, because the liquid is already at body temperature, so you are losing that heat energy when you pee
    Maybe so, but I think you'll find that it would be impractical. How long do you think you can "hold it" when it's freezing outside and ya got a full tank?

    It's unlikely that very much energy is being spent warming your urine because it was already at that temperature when it was...created...and there's a lot of body mass around your bladder to keep it insulated from the cold, not to mention continually warm.

    Also, there's not a lot of recirculation of blood happening around your bladder, so cold blood from your extremeties won't necissarily be taking advantage of your bladder's contents in any effective manner.

    Quote Originally Posted by rowan
    ...and also by peeing you are reducing your mass to surface area ratio (i.e a skinnier person gets colder faster than a fat person). all other things being equal (i.e you're not drinking anything)- who is right, and for what reason?
    :P

    Exactly how much "surface area" do you lose when you go from full to empty? You'd have to change size quite a bit to have any real effect on heat loss due to surface area change.


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  4. #3  
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    Two words: Kidney Damage.
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  5. #4  
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    Quote Originally Posted by Jeremyhfht
    Two words: Kidney Damage.
    LOL
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    i know you can't hold it in forever, but we're talking about peeing sooner vs peeing later. Given that heat loss is continuous in a cold environment, which strategy would confer the greatest thermanl inertia? i.e which would keep you warmer longer? i'm talking about the theoretical physics of it, otherwise i would have posted the question in the biology section.

    and i realise the change in surface area to mass ratio is very small, but so is the gain, if any, of getting rid of the urine. as skinny people get colder faster than fat people, i went with peeing later. also, the image of steam rising off your urine when you go made me think you MUST be losing heat when that happens. come on people, we're only talking theoretically here.

    surely someone knows the serious answer to this question, considering the complex nature of the other discussions i have seen on this forum
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  7. #6  
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    I don't think I can give a more serious response than I did in my first response.

    Beyond what I posted, empirical data is what's needed.

    What is the temperature of urine while internal?

    How many BTU's does urine in the bladder produce when the bladder is full?

    How many BTU's are transfered to the body from the bladder?

    How does the overall cooling of the body effect the temperature of the urine?

    Given that the bladder does not produce heat, the internal temperature of the urine is purely based upon how warm the body fluids are when converted to urine, and this temperature is maintained by the body's surrounding warmth. If this warmth fades, so too will the bladder's warmth. Since the bladder does not warm the urine, we must examine the thermal properties of urine.

    For example, does urine retain heat? How long after the heat source is removed will urine maintain an effective temperature?

    That all said, it's probably ineffectual to keep urine in the bladder as a way of keeping warm. The thermal benefit of a warmed liquid such as urine likely does not significantly effect the surrounding blood enough to have anything more than an extremely brief boost in temperature sustainment. Further, it is more likely that the urine will cool as fast, or faster, than the rest of the body. Although, again, the cooling is likely to be insignificant enough to make a difference either way.
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  8. #7  
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    I agree with your analysis. Hold it longer, for the reasons you already stated. The differences would be pretty trivial though.
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    ... surely someone knows the serious answer to this question
    I didn't know we were supposed to be serious!

    Anyway, the answer is...

    It doesn't matter!

    You are discarding a calculable number of BTUs along with some measurable mass. So what? There is normally no heat exchange, neither gain nor loss, between the stored urine and the body because they are the same temperature. Therefore the stored urine cannot be considered a heat reservoir. Thus, for purposes of body warmth, there is no value in storing it and no loss in disposing of it.

    Note that the solution would be different if applied to a cold-blooded animal, or to a carcass. I'm NOT going there.
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  10. #9  
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    Actually, our bodies want to pee when cold for a reason. Holding it in ends up using more energy, and releasing it helps the body compensate for the freezing temperature that exists on the surface. (I'm summarizing what I was recently told)
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  11. #10  
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    who is right, and for what reason?
    Neither of you is right. It's interesting though, that you both apply the same wrong argument in opposing ways (the key is that your urine is at body temperature, neither below, nor above).

    Your friend is wrong in assuming that energy is continuously used to keep bladder liquid at body temperature. Energy would be used only to bring urine *up* to body temperature, not to *keep* it there. The bladder is pretty well enclosed within the body. Heat loss to the environment only occurs at the surface. Even any additional liquid that enters the bladder is already at body temp.

    You are also wrong (though not entirely) in assuming that the energy loss through peeing has any effect on your body temperature. This would be true if the urine somehow helped to heat up the body but that's not the case. The urine is *at* (not above) body temperature, so loosing it will not change your average internal temperature. You are indeed loosing energy, but this is irrelevant as you're also loosing the mass that holds this energy. I said you're not entirely wrong because there is one small (probably insignificant) aspect to your position: You're loosing a small amount of heat capacity. The less mass (e.g. water) your body holds, the easier it looses heat to the environment. A liter of pee will not make any noticeable difference, though.

    What matters more in this situation (apart from the obvious effect of skin temperature) is the water you take in. If you drink something cold, your body will need extra heat to bring it up to the right temperature. Typically your body will actually create a little more heat than necessary which is the reason why an ice-cold drink in hot weather will give you only immediate short-term satisfaction. You're actually causing your body to heat up! Various peoples who live in hot climates prefer to drink warm (luke warm or even hot) liquids for this reason. It may be counter-intuitive, but folks who've had thousands of years experience really know what works.

    If you drink something hot, your body actually gains heat, which would increase your transpiration in hot weather. If it's not too hot (just above body temp so not to trigger an overreaction of your body) it may help you in cold weather as well.

    And here's another misconception: Alcohol keeps you warm. No, it doesn't. The burning sensation is similar to the feeling of heat but has nothing to do with it. Again, you're fooling yourself in the short-term. In the long term, alcohol in your blood has the effect of widening your blood vessels which has a desastrous effect on heat loss! You'll actually feel a lot colder, which starts a vicious cycle: You'll just keep drinking to get that immediate satisfaction, and you'll really get colder and colder.

    (one aspect on the side: of course any calories you take in will help as fuel for the body. With alcohol, unfortunately, the negative effects more than compensate for the benefit.)
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    There is normally no heat exchange, neither gain nor loss, between the stored urine and the body because they are the same temperature.
    Unless you are going into hypothermia in which case the extra mass might maintain your core body temperature a few seconds longer before you freeze to death.
    Actually, our bodies want to pee when cold for a reason. Holding it in ends up using more energy, and releasing it helps the body compensate for the freezing temperature that exists on the surface.
    I don't see how it would use more energy but if it did it would end up in the form of heat which would warm you up. Shivering used up energy too, but it also keeps you warm. Releasing what helps the body compensate? The pee or the energy?
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    i wasn't saying that urine 'heats' the body- i realise that it would be at body temp (not above or below)- at the time i was arguing that the reduction of mass would be more influential than any 'energy gain' (if any) you get from not having to keep urine warm. Is that a fair statement?

    steve and jeremy seem to disagree?

    what's a BTU?
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    the reduction of mass would be more influential than any 'energy gain' (if any) you get from not having to keep urine warm. Is that a fair statement?
    No, it's not a fair statement because it doesn't take any energy to keep it warm, and the reduction in mass does not hurt if you are maintaining a constant temperature.
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    There would only be a valid argument here if urine somehow had some positive thermal capacity. If that were the case, as your body temperature decreased, your urine might stay warm longer, and thus provide some source of heat.

    However, we're talking extremely small affects. Your urine in your bladder would have to be pretty hot in order to provide enough heat to warm the body.

    Even if the urine is warmer and stays warmer longer, the transfer of heat would be so small that you'd likely not be able to even notice a temperature rise anywhere beyond the vicinity of the bladder...so the affects would be effectively zero.

    As for holding it in vs letting it out...well, you probably waste a bit of energy dancing around.
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    Quote Originally Posted by Harold14370
    the reduction of mass would be more influential than any 'energy gain' (if any) you get from not having to keep urine warm. Is that a fair statement?
    No, it's not a fair statement because it doesn't take any energy to keep it warm, and the reduction in mass does not hurt if you are maintaining a constant temperature.
    so you're saying that, theoretically, if you could pee out say, 70 litres for arguments sake, leaving you paper thin and weighing about 5 kg, then you wouldn't cool down faster? how can a reduction in mass not be relevant? it's common knowledge that skinny people get colder faster for this exact reason.
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    Quote Originally Posted by Wolf
    There would only be a valid argument here if urine somehow had some positive thermal capacity. If that were the case, as your body temperature decreased, your urine might stay warm longer, and thus provide some source of heat.

    However, we're talking extremely small affects. Your urine in your bladder would have to be pretty hot in order to provide enough heat to warm the body.

    Even if the urine is warmer and stays warmer longer, the transfer of heat would be so small that you'd likely not be able to even notice a temperature rise anywhere beyond the vicinity of the bladder...so the affects would be effectively zero.

    As for holding it in vs letting it out...well, you probably waste a bit of energy dancing around.
    as i stated above, "i wasn't saying that urine 'heats' the body- i realise that it would be at body temp (not above or below)-"
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  18. #17  
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    I think we just explained that it has no value being kept.
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    but if it takes no energy to 'keep' the urine warm, then there clearly is value in keeping it because you are maintaining a greater mass and therefore you would have more thermal inertia (even if its a tiny advantage; that what we're discussing here). i would think that's almost self explanatory to anyone who passed year 11 physics?
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  20. #19 Re: pee or hold it in to stay warm? 
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    Quote Originally Posted by Wolf

    Exactly how much "surface area" do you lose when you go from full to empty? You'd have to change size quite a bit to have any real effect on heat loss due to surface area change.
    i just re-read this bit- the point is that your surface area DOESN'T change but your mass does- simple physics i thought. why do people have so much trouble with this? am i missing something?

    two objects (of same substance i.e. water) of equal surface area but different mass will cool at different rates. yes or no?
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  21. #20 Re: pee or hold it in to stay warm? 
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    Quote Originally Posted by rowan
    i just re-read this bit- the point is that your surface area DOESN'T change but your mass does- simple physics i thought. why do people have so much trouble with this? am i missing something?

    two objects (of same substance i.e. water) of equal surface area but different mass will cool at different rates. yes or no?
    They will cool at different rates, only due to the different thermal mass, but you don't want to cool down you want to stay at the same temperature. If your temp stays the same, there is no heat transfer from the urine. The rate of heat loss is proportional to the temperature difference and surface area, which don't change with mass.

    The reason larger animals are better adapted to the cold is not just their larger mass, but their greater mass of muscle and organs that are producing heat. Your urine is not a source of heat, until your temperature drops (hypothermia) in which case, as I said before, it helps a tiny bit.
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    That "tiny bit" has got to be practically unmeasurable. Especially since as your body cooled to the point of hypothermia, so too would the urine inside. It's temperature is regulated by body heat, so if that goes down, so too does the urine's temp.
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  23. #22  
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    Quote Originally Posted by Wolf
    That "tiny bit" has got to be practically unmeasurable.
    In cooling from your normal body temperature of 37 C to Stage 3 hypothermia, 32 C, a liter of water would lose 5 kcal of heat which is about the energy in 1.25 grams of carbohydrate.
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  24. #23  
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    hum, I'm not sure it makes that big a difference either way compared to other factors.

    "bodies want to pee when cold for a reason" the outer bloodvessels contracts, this insulates you as blood is not as much chilled by the cold outside your body but this causes you to store more liquid in the blader(not sure spelling) and you feel the urge.

    Sometimes what you should do also depends on the situation, if you are about/expecting to be cold or are already in hypothermia, or if you are dry or in water, if help is just around the corner or way off.

    ex: You dont want to be wet, so no overheating if you expect to be cold to avoid sweeting, but if hypo is starting you do want heat to offset the cold. Eat and drink a lot in a cold environment for energy and hydration, but if you are already in hypo the only energy you'll get from food(if any) is its temperature.
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  25. #24 Re: pee or hold it in to stay warm? 
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    Quote Originally Posted by Harold14370
    They will cool at different rates, only due to the different thermal mass, but you don't want to cool down you want to stay at the same temperature.
    exacty- i am saying that holding it in will make you stay at the same temperature for a tiny bit longer than if you expelled it.

    i don't know how many times i have to say this but here i go again:

    all other things being equal (i don't care about blood vessels retracting etc etc-that's why i posted this question in the PHYSICS forum).

    also, i know the effect is only tiny- i am discussing quality, not quantity

    regardless, this post is now useless for use as any sort of definitive answer because for some reason you people simply won't listen to the above bolded and underlined statments.

    i give up- maybe i'll ask Dr Karl. i'm sure he passed year 11 physics......
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