We have not been approaching vitamin D and the immune system correctly. 

Specifically, we haven’t been measuring, evaluating, and supporting proper usage of vitamin D correctly.

Vitamin D and your immune system are intimately connected BUT there is a lot more to that story.

The vitamin D that we consume or produce through sunlight exposure is not the active form that our body uses. 

By the time vitamin D has been converted to its active form in the body, it’s not even a vitamin anymore.

vitamin d

The active form of D that performs all the functions we need vitamin D for is actually a hormone.

An immunosuppressive class of steroid hormone called a secosteroid, to be more specific.  

This bears repeating. The vitamin D that actually performs the important tasks of calcium and bone regulation and immune functions is a hormone

It is no longer in the same form as when you ate the salmon with the vitamin D or the D that your skin produced by exposure to sunlight, or even the vitamin D supplement you took.

And it’s NOT the form that doctors check in your blood when they test your vitamin D. More on that in a minute.

Now, there are many forms and precursors to the active D hormone but for simplicity sake we’re going to focus on one, 25OHD. 

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vitamin D conversion

Vitamin D Conversion


When you eat foods with D, take supplements, or get sunlight, your liver converts that vitamin D into 25OHD. 

25OHD is what the doctor tests when you have your vitamin D levels tested. 

This is NOT the active form of D. We have NOT been testing the active form of D that is responsible for all the good that D does in the body.

(However, like everything in the body, it’s about balance and MORE does not always equal BETTER.)

25OHD then gets converted into 1, 25OH2D by the kidneys. 1,25OH2D is the active hormone (also called calcitriol) that is performing the functions of “vitamin D.”


We’ve been approaching vitamin D management incorrectly.

We have only been assessing levels of 25OHD and when they are low, doctors (and practitioners like myself – I am guilty of this before I recently learned this!) often suggest taking high amounts of vitamin D. Either in the form of D2 or D3. Doesn’t really matter.

“Low” Vitamin D

First of all, there is not a clear definition of normal or sufficient amounts of vitamin D, as several different institutes and organizations have very different ranges for what is low, normal, or high.

Also, “low” vitamin D levels can be seen in healthy and sick people. In healthy people, vitamin D can appear low but the 1,25 (Active form) is normal. In this case, the body is managing and balancing the active hormone and 25OHD stores just fine. 

Vitamin D levels can be low in sick people (those with autoimmune or other inflammatory issues) but their 1,25 (active form) is HIGH. 

This can be a problem.

Vitamin D as an immunosuppressant.

Studies are pointing to vitamin D as an immunosuppressant, which is why it seems like it is helping inflammatory conditions. Like any steroid, it can be helpful in the short term with symptoms but when we suppress the immune system too long, other problems arise. 

This makes supplementing with high amounts of vitamin D long term a very questionable (and I’d now say incorrect) action to take.

It was thought that low vitamin D was a cause of immune problems but it is actually being shown to be a result of inflammation. 

As the body becomes and stays inflamed from various causes (bacterial infections, intracellular pathogens like lyme or epstein barr virus for example, autoimmunity, etc), it converts more 25OHD into 1,25 to try to deal with that inflammation. 

Those infections, pathogens, etc. also block the Vitamin D Receptors (VDR) on cells, which causes the body to further convert 25OHD into 1,25 to try to up-regulate the VDRs into accepting the 1,25.

As with most aspects of inflammation in the body, this becomes a cycle!

What should we do about all this?

First of all, when low vitamin D is seen on a blood test and there are concerns of inflammation or infection in the body (infection is more common than you think and can be an under-the-radar problem if the person evaluating you isn’t aware of it), I suggest getting tested for 1,25OH2D. 

And because I much prefer to get a better whole-picture view of what’s going on, I’d suggest all the other tests I’ve written about here.

Then, we can determine if you truly are deficient in vitamin D (which would look like both 25OHD and 1,25 being low – but even then, it isn’t necessarily that you aren’t getting enough D, it might be related to co-factors needed for conversion. This is one more reason why it’s important to look at you as a whole, taking into account your other blood work levels) or if it’s more a matter of cleaning up inflammation in the body so that your body can naturally regulate levels of 25OHD and 1,25OH2D

vitamin d foods
When we clean up underlying causes of dysfunction and inflammation, it’s amazing how our bodies can regulate processes on their own! Instead of just trying to shove more vitamin D into the body that may be adding to inflammation instead of helping it, we want to bring balance and homeostasis to the body.

The human body is truly amazing and we need to stop just looking at things one dimensionally. Vitamin D synthesis and regulation is much more nuanced than just being low or high and needing more!

Phew, that was a lot. I’ll likely be following this up with more blogs on this topic! Comment below with your questions!

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