sunshine and vitamin d!

Okay, so I do realize that I've been MIA for a while.  And rather uninspired.  It's been busy!


For now, heads up.  Science post coming through!


But hey, the weather is warm and the sun is coming out.  So it's related!  Not only does the sun make you happy, but its UV rays help you make vitamin D, which in turn helps you absorb calcium, which is good for your bones.  Obviously.  So yes, UV rays in moderation help you maintain a healthy, strong skeleton (along with drinking milk and exercising, of course...uh oh, did somebody just say exercise?!).   Here's how it works.


There are two types of vitamin D, Vitamin D₂ and Vitamin D₃.  Vitamin D₂ we get from our diet.  Vitamin D₃ is produced in the skin with the help of UV rays.

Now that we’ve gotten past the role of the sun in the production of Vitamin D, let’s just look at Vitamin D as a whole.  Well, let's just say that here are many different forms, but we care about the active form, 1,25-dihydroxyvitamin D.  This happens in the kidneys, where 25-hydroxyvitamin D becomes 1,25-dihydroxyvitamin D.  I'll focus on 1,25-dihydroxyvitamin D's role in calcium regulation, one of its many roles, today.  So without going into too much detail - 

-Calcium is absorbed in the gut.  It goes from the lining of the gut into the bloodstream with the help of Vitamin D, which acts as a sort of receptor during the transport.

-You need to maintain a tightly regulated balance of calcium ions in your body, because calcium is used for pretty much every body process.  When calcium is absorbed in the gut, some of it says in the bloodstream and some of it gets stored in your bone.  But what happens when you don't consume enough calcium?  

PTH comes into play!  Your parathyroid glands (there are 4, and are located in your neck/throat area) have a calcium-sensing receptor.  When there's not enough calcium ions in your bloodstream, the parathyroid glands release parathyroid hormone, PTH, which tells your kidney to activate more vitamin D so your gut can absorb more calcium, makes you lose less calcium through your urine, and has your bone release calcium from your bone.

It is this release of calcium from the bone (to fuel your blood calcium balance!) that leads to the weakening of your bones.  And if you release too much calcium without putting too much back in, well, that increases your chance of getting osteoporosis.

And that is the simplified version of sunshine and Vitamin D.

I don't really have time to put up pretty pictures just right now.  Maybe later.


a good reference -
Holick, MF.  "Vitamin D Deficiency." New England Journal of Medicine 2007; p 266-81