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.
Here’s a little anecdote to give you a sense of how important we health professionals think vitamin D is. During the week I was writing this, I interviewed the noted psychiatrist and best-selling author, Dr. Daniel Amen, for another project I'm working on. Since, at the time of the interview, we were in the middle of the pandemic, I decided to plunge right in and ask Dr. Amen what he thought about the virus and the immune system.
“Dr. Amen," I said, “you and I are both in the age group considered to be at greatest risk for bad outcomes if we contract COVID-19. Are you personally afraid of the virus?”
He answered exactly the way I would have answered. “Well," he said, “I certainly don’t want to get it, obviously. It’s a nasty virus. But my vitamin D level is 73. I’m pretty sure if I did get it, I’d ultimately be OK.”
Time For The Usual Disclaimer
No one is saying that vitamin D cures or prevents coronavirus. I tell you that story to emphasize how important vitamin D status is as a marker of immune system function. 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
This Just In!
The very week I was writing this, a new study was published from Northwestern University showing that vitamin D plays a role in COVID-19 mortality rates.6 Right on the heels of that, the government of the UK just ordered an urgent review of the potential ability of vitamin D to reduce the risk of coronavirus, while the UK’s Scientific Advisory Committee on Nutrition (SACN) is reviewing recent evidence on vitamin D and acute respiratory tract infection in the general population.7
And just last April (2020), a paper was published by Ron Tucker, PhD, in the journal Hospital HealthCare Europe. It had the intriguing title, “Is Vitamin D an Important Biomarker for Symptom Severity in COVID-19?” Dr. Tucker stated the following: “Based on the latest analysis, it would seem eminently sensible for clinicians to ensure that those infected with COVID-19 have adequate vitamin D levels because this may lessen the effects of the virus and possibly save more lives.”8
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. (That’s why Dr. Amen was so happy his vitamin D level was 73!)
When you 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
And 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.