Vitamin D — Should You Be Taking It?
Should you be taking vitamin D? There's only one way to find out. Get your blood drawn and your level checked.
Your body starts making vitamin D when your skin is exposed to the sun. That vitamin D is converted first in the liver and then in the kidney. The best indicator of your vitamin D status is the blood concentration of the 25-hydroxyvitamin D that your liver makes. It reflects the amount of vitamin D produced by your body plus whatever you have taken in from foods and supplements. The 25-hydroxyvitamin D circulates in your blood for about 15 days.
Your kidney takes that 25-hydroxyvitamin D and makes 1,25-dihydroxyvitamin D. Even though this is the active form, it is NOT a good indicator of vitamin D status. It only lasts in your bloodstream for about 15 hours. The level is very closely regulated by other factors, such as your body's calcium and phosphate. Because of that the blood level of 1,25-dihydroxyvitamin D does not decrease until there is severe vitamin D deficiency.
Often if both levels are checked at the same time, the 1,25-dihydroxyvitamin D level will be adequate, but the 25-hydroxyvitamin D level will be extremely low.
Checking blood vitamin D levels is still fairly new. Many doctors still do not routinely order it. Until very recently it was thought that our bodies were getting adequate vitamin D from sun exposure and from our diets. From my own experiences, testing myself, family members, and patients, I can tell you that nothing could be further from the truth. What this means is that you must become your own advocate. Here is how:
- you must get your vitamin D blood level checked. If you are about to have your annual physical exam or some other blood test, ask that your vitamin D level be included, and
- you must check that your doctor orders the correct vitamin D form. Make sure it is 25-hydroxyvitamin D, or 25 OH D. Don't even bother to have the 1,25-dihydroxyvitamin D level checked. You will be wasting your time, money and blood.
Next....what level is normal? Optimal? Dangerous?
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