A PhD and RD Explains Why Your Vitamin D Level Might Be Stubborn (And What To Do)

If there were ever a nutrient to blow the minds of scientists, clinicians, and consumers over the past several decades because of its wide-reaching health impact, it would have to be the fat-soluble wonder vitamin D. And a la Dirty Dancing, nobody can put this fascinating nutrient in a corner. 

Though vitamin D was initially discovered (and somewhat pigeonholed) for its critical role in skeletal health, research over the past 40 or so years has demonstrated how truly vast a role it plays in our health—spanning from bones and muscles to our heart, brain, thyroid, reproductive organs, brain, gut, and more.*

The top culprit of what I'll dub "vitamin D resistance" is the absence of a truly daily vitamin D supplementation routine. Listen, we all get busy and miss the occasional day (Saturdays for me), and that's OK because vitamin D levels are resilient. (You can also double up with zero safety concerns if you miss a couple of days, by the way.) 

But, plain and simple: People who prioritize adherence to their daily D ritual consistently achieve and maintain healthy levels of vitamin D (i.e., a 25-hydroxyvitamin D level greater than or equal to 50 ng/ml).* That's assuming their supplement is high-quality and sufficiently potent, of course. 

Because vitamin D is one of those essential micronutrients that has a daily nutritional requirement, though, when we fail to honor that 24-hour period and operate on our own, semi-sporadic supplement schedule, our vitamin D levels pay the price.

When it comes to testing vitamin D status in healthy individuals (i.e., folks without medical issues, particularly those related to the liver or kidneys), the go-to status blood biomarker used in clinical practice to assess vitamin D status is total serum 25-hydroxyvitamin D, or 25(OH)D for short. 

What's important here is the word total. You see, total 25(OH)D is the sum of both vitamin D2 (ergocalciferol) and D3 (cholecalciferol) inputs. You definitely want the sum of the parts when measuring vitamin D status because different sources offer different types: natural and fortified foods and beverages can be either D3 or D2, sunshine is D3, medication is D2, and supplements can provide D3 or D2.

Not to mention, I have also seen cases in which people supplement with vitamin D2 (which is a bad idea; we explain why here) but their health care provider inadvertently ordered or only reported the 25(OH)D3 lab test result. This falsely made it seem like the vitamin D supplementation regimen was ineffective. I've seen the opposite mistake happen too.

While the individual pieces of the puzzle are informative (sometimes they're critical for understanding contributors to overall vitamin D status), make sure your lab report always includes the total 25(OH)D result.

To detect and treat vitamin D deficiency or insufficiency3, you need cutoffs. A total serum 25(OH)D level less than 20 ng/ml is vitamin D deficiency, while a result greater than 20 but less than 30 ng/ml is vitamin D insufficiency. Both are concerning results and should be calls to action.

So what goal should you aim for, then? Well, first of all, you'll want to avoid lingering around 30 ng/ml. Instead, aim for 50 ng/ml or higher.

Why? Board-certified endocrinologist Brittany Henderson, M.D., puts it this way: "As an endocrinologist, I know that achieving optimal serum 25(OH)D levels in the 50-plus ng/ml range is imperative for immune health, bone health, and more. It's difficult for most standard vitamin D formulations to achieve this."

As an R.D., I have talked to countless friends, clients, and strangers who are genuinely convinced that 30 ng/ml is the end goal for vitamin D health. It's a common misconception. Now you know: 30 is the cutoff to avoid, so aim higher. Research demonstrates that 5,000 I.U. of vitamin D3 daily in adults with a healthy weight (which, as a general rule of thumb is a BMI of 18.5 to 24.9) will get you to 50 ng/ml.

The next culprit of a stubborn vitamin D level is jumping the gun on testing. Here's a common scenario: A person gets their baseline vitamin D status result, receives the news that they're vitamin D insufficient or deficient, and starts taking a vitamin D supplement.* They are eager to correct the deficiency and thus, complete follow-up testing too soon. This will lead them to discover a (falsely and prematurely) low vitamin D result. 

So, what's too soon? The research and clinical consensus indicate that eight to 12 weeks is the time to wait (12 weeks, to be sure) to establish your new steady state of vitamin D. In other words, follow your vitamin D regimen daily for three months before undergoing a retest, if you want an accurate result.

For all you keto aficionados, passing the fat is a regular mealtime practice. But fats are relevant to supplement consumption, too.

Vitamin D is, by design, a fat-soluble micronutrient, which means it's optimally absorbed in the gut when some fat is consumed with it, or directly before taking it. In fact, the question of how to time your vitamin D supplement is less about a.m. versus p.m. and more about when there's some fat around. Without it, your absorption pays the price!

At mindbodygreen, we intentionally bypassed this scheduling variable altogether with vitamin D3 potency+. In this thoughtful and innovative formula, we bring the fats to you by incorporating a trio of organic oils from avocados, flaxseed, and olives (bonus: healthy omega-3 and omega-9 fatty acids), to promote the absorption of the vitamin D3, which is sourced from organic algae.*

Speaking of vitamin D supplements, a poorly designed one can also be the culprit of stubborn vitamin D levels. Talk about counterproductive. To avoid a weak-sauce formulation and low vitamin D levels in your body, make sure your vitamin D supplement optimizes these features:*

Just like with basketball free throws, follow-through is everything when it comes to supplementing with vitamin D. And for your supplement to have a shot at scoring (aka increasing your baseline status), you need to follow through.* 

This might sound similar to previous culprits, but I'm actually talking about adhering to your supplement routine and retesting beyond those first three months. 

Addressing vitamin D inadequacy is often discussed and treated like it's a problem you put a Band-Aid on—but unless you're putting a Band-Aid on every day for life, that analogy breaks down rather quickly. Achieving and sustaining vitamin D status is a lifelong, proactive wellness choice. When supplementation is treated as a temporary fix, your 25(OH)D levels will drop, sometimes back to baseline or lower. This yo-yo-ing phenomenon is something to avoid.

Adiposity, or the amount of body fat one has, is one key facet of body composition (as are lean mass and bone density). Research has repeatedly demonstrated that fat tissue is inversely correlated with vitamin D status (i.e., higher adiposity, lower vitamin D levels).

The reasons are numerous and still shaking out via emerging research. One major factor is that fat tissue has a tendency to store fat-soluble compounds like vitamin D, making less of this essential nutrient available to circulate and be activated to support our cells, tissues, and organs throughout the body.*

The pragmatic bottom line here: Sub-potent vitamin D dosing that lacks personalized consideration for body composition (specifically moderate to higher adiposity) is very common.

Clinical guidelines indicate that individuals with overweight and obesity require up to two to three times more vitamin D3 each day to achieve healthy 25(OH)D levels.* Partnering with a health care practitioner is important to fine-tune your personalized approach, but this means that 10,000 I.U.-plus of vitamin D3 would be a reasonable daily dose.*

What about other "buddy" nutrients that affect vitamin D status? While vitamin K2 sometimes finds its way into vitamin D3 supplements, it has nothing to do with vitamin D absorption, bioavailability, or status.

Additionally, while vitamin D supports calcium absorption and levels (and both nutrients are hallmark bone essentials),* the converse is not true. Vitamin D does not depend on calcium for absorption.

Interestingly though, another essential macromineral does require our attention. I'm talking about magnesium (which over 40% of American adults1 fail to meet their daily needs through diet).

Suboptimal magnesium status is relevant to vitamin D because the mineral is required for binding 25(OH)D to the vitamin D binding protein (VDP) for circulation around the blood and delivery to tissues throughout the body. Magnesium is also required for the conversion of 25(OH)D to the active 1,25(OH)2D hormone form. Both of these mechanisms will affect vitamin D status. 

Plus, as Crouch sagely warns: "Magnesium deficiency and insufficiency are often missed due to conventional lab testing techniques."

The takeaway here: Accurate testing and optimizing magnesium status4 appear to be critical for vitamin D to flourish.

I've said it before, and I'll say it again: Every person's vitamin D response is individualized (hello, genes). And while the above intel and recommendations to solve stubborn D levels are pertinent to most people, they are not to those individuals with specific medical issues. In fact, sometimes vitamin D deficiency can be a clue to such issues before they're even diagnosed.

For example, there could be a gastrointestinal issue that has significantly reduced viable surface area for vitamin D absorption in the gut. Or, perhaps a problem causing suboptimal liver or kidney function. (These two organs are involved in the major steps that convert vitamin D into its circulating form and active, hormone form.)

Interestingly, a compelling body of research has even revealed an inverse relationship between inflammatory pathways in the body5 and vitamin D status. (They likely mess with its normal metabolism and utilization and increasing one's D needs.)

If you believe these or other health issues may be contributing to your vitamin D resistance, urgently partner with your health care provider. 

Some vitamin D facts are simple—like we can't get enough from our diet to move the needle, so we need a daily D supplement to achieve and sustain sufficiency.* But what if something more complex is causing your vitamin D levels to be resistant or stubborn? Consider these 10 key contributors (and solutions) to stubborn vitamin D levels so that you can get them up and keep them there.*