Vitamin D and Bioindividuality: Why Testing is Critical

The Rise of Vitamin D

Vitamin D has become one of the most popular and commonly purchased dietary supplements over the past decade, with the pandemic and increasing awareness of its robust immune-supporting properties further amplifying its popularity. The attention is absolutely well-deserved; vitamin D plays a role in nearly every aspect of human health, supporting everything from bone density and immune function to mood and gut health. Fun fact: nearly every cell in the human body has a receptor for vitamin D (Bikle, 2016).

Recently, anecdotes of toxicity have garnered attention, highlighting the fact that even when it comes to micronutrients like vitamin D, more is not always better. In a recent Medscape article, the author reviewed 16 cases of vitamin D toxicity in Spain, ultimately linked to a low-quality supplement that had a higher dose than what was listed on the label. The hospitalized patients were found to have elevated levels of vitamin D as well as acute kidney failure and elevated calcium levels. Reports like the one underscore the need for caution when taking supplements, and here we’ll take a closer look at vitamin D in particular.

The Dose Makes the Poison

It’s important to remember that “natural” does not necessarily mean “safe.” It’s logical to think that if something is good, more must be better, but this can be a dangerous idea when it comes to vitamin D. Fat-soluble vitamins, unlike their water-soluble counterparts, build up in the tissues, which can be problematic when taken at high doses for extended periods of time. Vitamin D toxicity can lead to significant problems, including hypercalcemia and disruption of normal bone metabolism. In rare cases, people can even experience acute kidney failure necessitating hemodialysis (Asif & Farooq, 2023). In less severe cases, there may be subtler symptoms like fatigue or malaise. Bottom line: vitamin D is a goldilocks micronutrient; we don’t want the level to be too low, too high, but just right.

The Importance of Bio-individuality in Functional Medicine

Bio-individuality is a pillar of functional medicine and it refers to the idea that we all have unique biological and physiological needs. This is particularly salient when it comes to vitamin D. Vitamin D doses need to be tailored to the individual, considering the following factors:

• Genetics, particularly vitamin D receptor single-nucleotide polymorphisms
• Health conditions, including autoimmunity, psychiatric conditions, obesity, and disease states that impair absorption ie: IBS, IBD, Celiac disease
• Lifestyle factors like sun exposure, diet, latitude, skin tone

Test Vitamin D Levels, Don’t Guess

So how do we decide what dose of vitamin D to take (or recommend)? Another popular slogan in functional medicine rings true—test, don’t guess. While many consumers take vitamin D supplements without proper guidance, using blood testing to inform treatment is crucial. The preferred test to determine vitamin D status is 25(OH)D and can be obtained from any local laboratory. While optimal ranges differ by source, the most common lab range is 30-100 ng/mL and functional medicine providers typically target a tighter range, commonly ~40-80 ng/mL.

As important as the initial test is monitoring levels over time. As described above, vitamin D absorption can be impacted by numerous factors. Therefore, 5 patients who have the same baseline 25(OH)D levels may have radically different levels in 8-12 weeks after taking the same dose of vitamin D. This is where personalization is key. Whereas one person may require a higher dose to achieve an optimal level, another may need to dial down the dose to avoid toxicity. It is not uncommon for functional medicine providers to monitor levels twice per year to ensure appropriate maintenance dosing.

Prioritizing Quality Supplements

A common criticism of integrative and functional medicine is that supplements are not regulated the same way medications are, making them inherently unsafe. This, however, is an oversimplification that overlooks the high standards many supplement companies uphold in terms of purity, potency, and transparency. In the case of vitamin D, we can safeguard against cases of toxicity like those mentioned above by recommending products that are third-party tested and GMP-certified.

Concluding Thoughts

Supplements, including vitamin D, can be transformational when used intentionally; they should not be taken haphazardly or “just in case.” When it comes to vitamin D, basing the dose on serum 25(OH)D levels and monitoring regularly is of the utmost importance to avoid problems, including toxicity. Patients should be encouraged to work with providers trained in the nuances of vitamin D dosing, monitoring, and metabolism. Psychiatry Redefined’s functional psychiatry training equips providers with the knowledge and tools to safely optimize vitamin D, helping patients get the benefits while avoiding the risks.