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Why do we need vitamin D?

  1. Jan 2, 2010 #1
    We all know about some of the important roles vitamin D plays in the body. The question is why the body uses vitamin D (or rather calcitriol which the body produces from Vitamin D) to act as a switch to turn on the production of certain proteins that are involved in the absorption of calcium from our food? If these proteins are so important, why is the production of these proteins made dependent on vitamin D? :confused:
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  3. Jan 2, 2010 #2


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    Because we evolved on a planet with a sun? If we'd evolved underground, we'd have a different mechanism.

    IU'm not really sure why you're asking 'why?'.
  4. Jan 3, 2010 #3
    You don't get any vitamin D at all at higher lattitudes during the winter months and part of spring and fall. In Canada everyone is adviced to take vitamin D supplements (people with a dark skin during the whole year). This is because there is now a lot of evidence that the higher level of vitamins D that people have at lower lattitudes play a role in preventing some diseases (to keep your bones healthy you don't need such high vitamin D levels).

    Vitamin D only activates certain genes. The question is then why the body has evolved to use vitamin D which you can so easily get a shortage of.
  5. Jan 3, 2010 #4


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    Do you mean in modern society, or in human history? It's a bigger problem now that we spend more time indoors.

    The body has a number of dependencies, Vitamin C for example. What is special about this one?
  6. Jan 3, 2010 #5
    it seems vitamin D has been with us for a long time, but we're not entirely sure why.

    i think it's also fairly new knowledge that vitamin D receptors are ubiquitous throughout the body.

  7. Jan 3, 2010 #6
    I think vitamin C is directly participating in anti-oxidation processes. But as I understand it, vitamin D does nothing more than to act as a signal telling cells to produce certain proteins that are involved in regulating calcium absorption from food, regulate the immune system etc. as the article quoted by Proton-Soup mentions.
  8. Jan 4, 2010 #7


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    Remember that humans have lived in a warm a and sunny climate for most of our history, so getting enough vitamin D was not a problem. This means there was no evolutionary pressure to "develop" an alternative mechanism.
  9. Jan 4, 2010 #8


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    More eloquently put than mine.
  10. Jan 4, 2010 #9

    It is not clear to me why evolution would have led to all higher organisms making very critical processes dependend on vitamin D given that one can easily get shortages and given that the vitamin D derived calcitriol only acts as a mere switch. It is like a company hiring very highly skilled personell to do trivial work that could be done by everyone or be completely automated.

    The only explanation I can think of is that there is evolutionary pressure against using easy to produce compounds to regulate the processes that vitamin D regulates. If the receptors to which calcitriol binds were replaced by different receptors so that other molecules would bind to it and those other molecules would be manufactured without sunlight by certain cells in the organism itself, then perhaps this process would be very vulnerable to diseases in which the molecules are overproduced.
    Last edited by a moderator: Apr 24, 2017
  11. Jan 5, 2010 #10
    i'm not sure why it should be so easy (in evolutionary terms) to get shortages of vitamin D. it's fat soluble, and we do a pretty good job of storing it up. in fact, the fatter you are, the harder it is to get vitamin D levels back up to normal if you were low. the fat simply acts as a sink. this is great if you spend your summers in the sun, with a minimum of clothing, eating the seasonal abundance, getting fat and storing up vitamin D. then in leaner times of winter, you can survive off your stored fat and vitamin D.

    as for why vitamin D, maybe it just started off as a signal of energy availability. this makes perfect sense if you're zooplankton, as the UV forms as soon as your cholesterol gets exposed to a bit of UV. and for us higher organisms, it still may function as a proxy for energy availability.
    Last edited by a moderator: Apr 24, 2017
  12. Jan 6, 2010 #11
    Great question.

    I agree that fat solubility must be part of the answer. Any vital nutrient that can be stored in fat improves survivability in cold environments, thus is "favored" by natural selection.

    But I think there must be a deeper aspect to. I'm thinking something unique about molecular properties that can only be derived by a UV photo-initiated synthesis process.

    Just some thoughts...RP
  13. Mar 8, 2010 #12
    I think vitamin D helps in fat-soluble prohormones. Other sources are D2 and D3 as well. Finding the best vitamin supplements is directly correlated to the purpose of intake.
  14. Mar 8, 2010 #13
    What about the thousands of years of ice age?
  15. Mar 8, 2010 #14


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    Ice age does not directly equate with lack of sunlight.

    1] Take note that cold days are often actually associated with sunny days. Clouds keep heat in. Clear skies let heat out.

    2] Ancient man did not have the luxury of ordering pizza and "cocooning" during cold spells. One could conceivably argue that ice ages might see a rise in sun exposure, since they'd have to spend more time hunting for scarce food.
  16. Mar 8, 2010 #15
    The question is really why e.g. immune cells have evolved in such a way as to be activated by vitamin D. If you have enough Vitamin D the part of your immune system that actively seeks out new threats and destroys them becomes more active.

    Perhaps this is because of Proton Soup's energy argument. A more active immune system uses more energy. A shortage of vitamin D could be associated with the Winter season and the prosepect of food shortages. Under those conditions, you may want to build up or conserve fat reserves rather than using energy to let your immune system work overtime.
  17. Mar 11, 2010 #16
    True, but Ice Age doesn't mean go outside in shorts. They'd be generously rugged up.
  18. Mar 15, 2010 #17
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