Nothing in the body works properly if your vitamin D levels are low—and this is especially true when it comes to the immune system.
See, the immune system is like Goldilocks and her soup—it has to be not too hot and not too cold in order to be performing just right. If your immune system is too stimulated (i.e., it’s running too “hot” and attacking everything in sight), you wind up with autoimmune disease. If your immune system is too sluggish and not responding quickly enough (i.e., it’s running too “cold”), you get sick.
The Ultimate Balancer
Vitamin D is the ultimate immune system balancer. It’s like Goldilocks cooling the soup when it’s too hot and warming it when it’s too cold. There are receptor sites for vitamin D on all kinds of immune system cells, including antigen-presenting-cells, T cells, B cells and monocytes.1 Vitamin D goes in there, takes the temperature of the soup and makes the necessary adjustments, helping to keep the immune system from over- or under-reacting.
Time For The Usual Disclaimer
Increasing vitamin D in someone who already has optimal vitamin D status won’t confer any additional benefits, that’s true.2 But—and there’s a big but here—most people aren’t even close to having optimal status.3
Most of us in functional medicine and functional nutrition think the government standards for “deficiency” are far too low. It’s possible to avoid being clinically deficient in a nutrient, but still be way under the number necessary for optimal functioning, just like it’s possible to avoid the technical definition of “poverty” and still have an impoverished life. Low levels of vitamin D have been associated with multiple health issues.4,5
Are you getting enough?
You can get an inexpensive blood test for vitamin D from your doc, but make sure you get the 25(OH) vitamin D blood test. Most experts consider a result of 50 to 80 nmol/L optimal. And when you do supplement, make absolutely sure you’re taking vitamin D3 (cholecalciferol), not vitamin D2, which is what they usually use to “fortify” foods and is much less absorbable by the body.9,10
Beyond immune system support
While the focus of this article was the immune system, let’s remember that vitamin D3 has an impressive resume of functions above and beyond supporting immunity. It’s also important for the heart and for the bones. In fact, vitamin D3 is often combined with vitamin K2 because both help keep calcium in the bones where it belongs, and out of the arteries where it doesn’t.