Why a 25-Hydroxyvitamin D Test May Be the MOST Important Test Your Doctor Can Give You
Vitamin D is an extremely important nutrient for our bones, and is coming to be understood as vital in other areas of our body as well. Traditionally, vitamin D was not a nutrient anyone would lack, and it is not considered “essential” because our body can produce it itself.
This requires sunlight, however, which many people do not get enough of to synthesize the proper amounts of vitamin D. Without producing enough vitamin D, we begin to become deficient, and it takes a toll on our health.
Vitamin D is actually a precursor hormone, and once we either form it in our skin or ingest it, it will be converted a couple times before it reaches its final hormonal state. First, in the liver, it gets converted to a form called 25-hydroxyvitamin D, or calcidiol.
This is the form you can get tested for to detect whether you are deficient in vitamin D or not. Then, in the kidneys, it gets converted to its active form, calcitriol. Calcitriol binds to specific receptors in the body and alters gene expression, allowing vitamin D to exert its beneficial effects.
Vitamin D And Bone Health
Vitamin D is noted for its benefits to bone health more than any other effect. Through at least two mechanisms, vitamin D directly affects how strong your bones are.
Almost every nutrient we ingest gets absorbed by the small intestine through proteins called “active transporters”. Active transporters are highly specific–they’re like square holes, round holes, star holes, etc. You can’t fit a round peg through a square hole, and calcium can’t be absorbed using a sodium transporter–it can only be absorbed using calcium transporters.
The amount of calcium we absorb is limited to how many calcium transporters are active in our gut during ingestion, which is dependant on a two important things: how much calcium is in the food, and how much vitamin D is in our body. The reason vitamin D is so important is because it turns on the transporters for calcium, effectively creating more “round holes” for the calcium to go through.
This means that when vitamin D is at a proper level, much more calcium is absorbed from your food. In fact, people in a vitamin D deficient state might only absorb 10-15% of the calcium in their food, compared with 30% for people who are vitamin D sufficient!