Over the past decades, our collective awareness of the importance of vitamin D has undergone a much-needed revival. While vitamin D was always known to be an essential nutrient, it was mostly ignored outside of the concern for bone health.

If you heard growing up to drink your milk to keep bones strong, then you received the full education on vitamin D (for which milk is fortified with) that modern medicine had to offer at the time. We now know so much more about what the body really needs, and it isn’t milk!

Thanks to a surge of research, the testing, and treatment of vitamin D deficiency have skyrocketed. However, with an estimated 40% of people deficient, many likely remain undiagnosed and untreated.

In addition, low vitamin D is more likely in certain groups of people, including the elderly and those with chronic illnesses.

In my own practice, I regularly screen for vitamin D deficiency. My experience is that individuals struggling with multiple debilitating health conditions are at higher risk for a deficiency which, in turn, can exacerbate their health which is already unstable. Testing and addressing vitamin D is one piece in the complex puzzle that the functional medicine approach is uniquely poised to treat.

Much has been said about the role of vitamin D in bone health and immunity. While those functions are critical, vitamin D impacts many other bodily systems. In this article, I’d like to take a fresh look at some of the lesser-known functions of vitamin D and its place in treatment for complex illnesses.

While vitamin D isn’t a miracle cure, it is often an integral part of the big picture of long-term health and healing. But first, a brief look at the basics.


The Wonders of Vitamin D

Most known as the sunshine vitamin, vitamin D is an essential fat-soluble vitamin found in small amounts in fatty fish, liver, and egg yolks.

Because it is not widely available in food, the body has the incredible ability to synthesize this vitamin for itself. When uncovered skin is exposed to UVB rays from sunlight, it triggers the conversion of a specific type of cholesterol to vitamin D. Humans are designed to thrive on sunlight, which is a special link we share with the natural world.

Unfortunately, this impressive natural ability is hampered by a number of factors, including:

  • Weather
  • Geographic location
  • Skin melanin content
  • Age – we tend to become less able to create vitamin D from sunshine as we get older
  • Concerns over the damage caused by excess sun exposure

Adequate vitamin D is essential for the absorption of calcium, healthy nerve and muscle signaling, as well as immune function (plus so much more!). When vitamin D levels are chronically low, deficiency symptoms develop, including:

  • Fatigue
  • Bone pain
  • Muscle weakness
  • Mood changes
  • Chronic infections

If deficiency becomes severe, bone disorders such as rickets or osteoporosis may develop. Thankfully, bone deformities from rickets are uncommon in our country. However, that does not mean we’ve solved the problem of vitamin D sufficiency.

People spend less and less time outdoors, and due to our awareness of skin cancer risks, many people load up on sunscreen, effectively halting vitamin D production. I certainly don’t advocate for indiscriminate sun exposure. But, I do work with my patients to normalize their vitamin D levels because its impact on conditions such as MCAS and infections is significant.


Vitamin D And Mast Cell Activation Syndrome

The main pathway by which vitamin D functions is through interaction with vitamin D receptors (VDRs). VDRs are located in almost every tissue of the body. When vitamin D binds with a VDR, it sends a signal to the cell, turning on or off genes within the DNA.

By regulating gene expression, the interaction of vitamin D and VDRs influence hundreds if not thousands of body functions. From encouraging the absorption of calcium to promoting the development of immune cells, vitamin D has wide-ranging effects depending on the type of cell it binds with.

Mast cells contain VDRs and are therefore responsive to vitamin D. When vitamin D binds with VDRs on mast cells, it signals the cells to decrease the production of pro-inflammatory mediators, among other actions. The result is more stable mast cells, making them less reactive to common triggers.

For people with mast cell activation syndrome (MCAS), the stabilizing influence of vitamin D is essential. While it is difficult in many cases to determine the exact cause of MCAS, vitamin D deficiency may play a role. Without the soothing signals from vitamin D to calm mediator production, mast cells are vulnerable to inappropriate activation and chronic release of inflammatory and allergic mediators.

The action of vitamin D on mast cells provides another avenue for the effective treatment of MCAS, which I find hopeful for my patients dealing with this syndrome. When we dive deep into what is really happening in the body, there is much we can do to rebalance and restore the mast cells to their stable state. Vitamin D is one key player.


Vitamin D and Chronic or Acute Infections

The role of vitamin D in immune function is a relatively new area of study. Historically, the most obvious sign of vitamin D deficiency was rickets or the deformation of bones. Significant emphasis was placed on the importance of vitamin D for bone health and the prevention of rickets back when science first discovered essential nutrients.

While prevention is undoubtedly important, the truth is rickets develops at the extreme end of the deficiency spectrum. Long before you notice changes in bone formation, many of the subtle actions of vitamin D could be compromised.

The public health focus on bone health created a lack of awareness of vitamin D’s critical functions in other essential body systems. And, because the level of deficiency that leads to extreme complications such as bone deformations is so low, less attention was given to the impact of mild deficiency.

Thankfully, recent research is now filling the gap.

The body produces a wide variety of immune cells, each with its own unique function. Most types of immune cells contain vitamin D receptors (VDRs) and respond to signals from the binding of vitamin D. In addition, vitamin D is essential to balance the immune system, causing the release of more anti-inflammatory mediators and fewer pro-inflammatory mediators.

When you have enough vitamin D, the immune system is primed to provide superior protection against infections and inflammatory responses. Conversely, low levels of vitamin D sets up the immune system in a way that may contribute to chronic or acute infections.

New research raises the question of how vitamin D influences inflammatory and immune responses and how altered inflammatory or immune responses may interfere with vitamin D. One theory proposes that chronic infections, such as those found in tick-borne and Lyme infections, may disrupt normal vitamin D metabolism. Even with enough vitamin D, the body may not metabolize it to its useful form.

What can happen is a patient gets trapped in a cycle of too little vitamin D to support healthy immune function along with poor immune function preventing vitamin D from working. This is a prime example of the complexity of the patients that come to me seeking help. One condition can build off the next, creating a self-perpetuating cycle of illness.

What is needed is a comprehensive and collaborative treatment approach to bring these patients back to health.


The Vitamin D And Covid-19 Link

A new area of vitamin D research has shed light on the interplay between vitamin D and chronic or acute infections. With the emergence of Covid-19 has come a whole new population of people impacted by infectious disease, whether mild or severe.

One study of patients admitted for COVID-19 found those who had low levels of vitamin D before becoming infected were more likely to have severe or critical disease. Almost 50% of enrolled patients with low vitamin D experienced severe COVID-19, compared to only 10% of patients with adequate vitamin D. These numbers, while not unexpected, are profoundly revealing.

Even more specifically, a recent review that examined the evidence surrounding vitamin D’s impact and mechanism of action on infectious diseases, including COVID-19, came to this conclusion:

“…the comprehensive finding of the current review shows a possible significant impact of vitamin D supplement as a hope in preventing, treating, and/or improving the progression of certain infections…” Taha R, Abureesh S, Alghamdi S, Hassan RY, Cheikh MM, Bagabir RA, Almoallim H, Abdulkhaliq A. The Relationship Between Vitamin D and Infections Including COVID-19: Any Hopes?. Int J Gen Med. 2021;14:3849-3870

The new data linking vitamin D with resistance to and resilience from infectious disease provides great hope for anyone battling chronic infections.


The Genetic Link

A subset of people with vitamin D deficiency have trouble maintaining adequate levels due to genetic mutations. There are a number of different mutations that affect VDR genes. VDR genes encode vitamin D receptors to bind and respond to vitamin D and are, therefore, an essential part of vitamin D status.

Mutations in these genes may negatively impact the ability to benefit from vitamin D. For example, individuals with specific VDR mutations have been shown to be at a higher risk for certain immune or allergic disorders. If cells do not receive proper signals from VDRs, their ability to carry out critical immune functions may be inhibited.

These genetic variations are something I watch carefully in my patients. The treatment for those with VDR gene mutations may be different compared to those with vitamin D deficiency related to lifestyle factors.

Often higher doses of vitamin D may be required to achieve the same effect that others might achieve at lower doses. Comprehensive monitoring is also of benefit for these complex patients.


Vitamin D In Practice

It has become clear that vitamin D is more complex than a first glance suggests. In many ways, this is good news for those dealing with chronic health conditions. Vitamin D may have a role to play in the recovery process and could be a missing piece in unraveling the full picture of their disease.

In my practice, I work with patients to leave no stone unturned as we seek out the source of their illness. To return to good health, we must address the causes at the root of multisystem disease and chronic infection. Rarely is there just one instigator. More often, I see people dealing with several infections, co-infections, MCAS, and autoimmune conditions that have been years in the making and even more years in diagnosing.

Vitamin D is not a magical cure, but it is a critical nutrient that can exacerbate the cycle of complex disease. Functional medicine provides a framework that looks at both the big picture and the smallest nutrients.

If you’ve been struggling to find the help you need, you are not alone. We treat the whole person in my practice, and I am deeply committed to partnering with you to find answers. Make an appointment to meet with me to start on the path to healing.