Vitamin D Deep Dive: Why Your Immune System Isn’t Protected

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A comprehensive study in 2018 found that as much as 40% of the population has measurable vitamin D deficiency. Why is this a problem?

Vitamin D plays a critical role in cardiovascular function, mood, fertility, and immune function. So how did we end up with such rampant insufficiency and what can we do about it?

In this article, you’ll learn exactly what vitamin D is, how it can improve your health, and what you can do to get your levels where they need to be.

What Is Vitamin D?

The name vitamin D is kind of a misnomer. Vitamin D actually functions more like a hormone, and is produced by the kidneys. At a minimum, vitamin D primarily controls blood calcium concentration, this keeps your heart beating and blood pressure levels normal.

When vitamin D levels are optimized, it actually has dozens of other functions, including supporting the production of immune cells, and a stable mood. You can get more vitamin D by eating the right foods, with vitamin D supplements, or by spending more time in the sunlight.

Vitamin D deficiency is serious, and vitamin D deficiency symptoms include increased susceptibility to infection, as well as mood disorders, and even hair loss.

D3 Vs. D2

There are a few different types of vitamin D, and you’ll learn which one is important to measure, and which type you should be Vitamin D Benefitsconcerned about.

Vitamin D has two variants: D2 and D3. The active form of vitamin D (meaning, the one your body can use right now) is 1,25 dihydroxy vitamin D (1,25 D) or calcidiol–you may see this appear on a test as 25 D or 25(OH) Vitamin D3.

Vitamin D2 (ergocalciferol) is an inactive precursor for vitamin D, which can be converted to active vitamin D in the kidneys. Previously, it was thought that D2 and D3 were equal in function, but we now know that D2 is only about 50-60% as effective as vitamin D3 in supplementation. 

Browse D3 supplements in the CentreSpringMD shop.

Vitamin D Benefits

Hundreds of different genes possess receptors for vitamin D, indicating that vitamin D is active throughout the body. The following are the benefits of vitamin D. 

Vitamin D and Immune Health

Adequate vitamin D benefits overall immune function and the health of specific immune cells.

Vitamin D is important for modulating both adaptive and innate immune response via receptor sites on the surface of B- and T-cells, two classes of immune cells (1). 

Studies have shown that vitamin D deficiency is associated with increased susceptibility to infection, and can impair the maturation of healthy white blood cells, which help the body to fight illness (1). Integrative medicine has long recognized the functional benefits vitamin D has upon proper immune function.

A meta-analysis of 25 studies containing more than 10,000 subjects found that vitamin D supplementation reduced the risk of acute respiratory infection across all patients participating (2). Vitamin D benefits other parts of the immune system as well…

Vitamin D and Autoimmune Conditions

Deficiency in vitamin D is also associated with higher rates of autoimmunity, and this may be due to its effect upon immuno-modulatory T-cells.

Autoimmune diseases including multiple sclerosis, rheumatoid arthritis, alopecia areata (hair loss), and lupus are impacted by the function of T-cells and vitamin D deficiency.

Now, this doesn’t mean that vitamin D will protect you from developing autoimmunity, or from experiencing a flare-up, but we do know that adequate vitamin D levels benefit the healthy function of immune cells, which in turn decreases risk for autoimmunity. 

This is why your functional medicine provider at CentreSpringMD will test for nutrient deficiencies when working with you to get your autoimmunity into remission.

Vitamin D and Metabolic Health

“Vitamin D deficiency plays a role in a multitude of chronic conditions, including type I diabetes, rheumatoid arthritis, hypertension, cardiovascular disease, and several common deadly cancers.” according to one study (3).

Vitamin D’s role in regulating calcium homeostasis plays a direct role in insulin secretion, which is a factor for both Type I and Type 2 diabetes. 

What’s more, obesity, diabetes, and insulin resistance can negatively impact kidney function, hindering the kidneys ability to convert inactive vitamin D2 precursors to its metabolically usable form.

Vitamin D and Mood

Depression affects nearly 7 percent of the adult population in the united states, and is the single most significant cause of

Vitamin D and mood

disability in this country. Additionally, the appropriately named Seasonal Affective Disorder (SAD) affects anywhere from 10 to 20 million people a year. 

Could vitamin D play a role in the health and regulation of our mood?

In one study, vitamin D supplementation supported mood and an improvement in depressive symptoms similar to treatment with light therapy, which is standard for treatment of SAD symptoms (4).

Patients with depression and other mood disorders also have markedly lower levels of serum vitamin D levels when compared to healthy controls. A truly integrative medicine approach to treating mood disorders will factor in nutrient status, including vitamin D levels.

Vitamin D and Hair Loss

Some hair fall every day is normal, and is part of a follicle moving through each phase of hair growth. But if you’re starting to notice more hair than usual in your hair brush or the drain, you may have one type of hair loss that can be affected by vitamin D and T-cell mediated immune function.

Alopecia areata is an autoimmune condition in which hair falls from the scalp in round patches all over the head. This is a little different than other types of hair loss due to things like stress, PCOS, or pregnancy, for example. 

Alopecia areata is associated with reduced vitamin D levels, but researchers are still working to find out why exactly this is (5). 

Vitamin D and Weight Loss

Postmenopausal women who were participating in a weight loss program lost on average 5 more pounds during a 6-week period than women whose vitamin D levels were not brought up to a healthy baseline (6). 

This means that women who are having trouble losing weight should consider whether increasing their vitamin d could help with loss efforts. 

Obesity also increases the risk for vitamin D deficiency, which could also be a double-edged sword for effective weight loss. On any weight loss journey, it’s important to optimize micronutrients to support a functional approach to healthy weight loss.

Symptoms of Vitamin D Deficiency

If you’re experiencing any of the following, it’s best to talk to your integrative medicine practitioner to get a blood test. From there, they can recommend the best course of action to get your vitamin D levels back up, and provide a followup test to check your progress. Vitamin D deficiency symptoms include:

Depressive symptoms or changes in mood

Vitamin D plays a role in managing mood, and patients with depression have been shown to have decreased levels of vitamin D.

Frequent sickness

Vitamin D is essential for regulating immune function, and healthy T-cell mediated immunity

Hair loss

Studies show low levels of vitamin D in individuals with alopecia areata, a type of autoimmune hair loss.


Vitamin D has been shown to improve symptoms of fatigue in otherwise healthy individuals (7)

Worsening asthma symptoms

Studies show a high prevalence of vitamin D insufficiency in children with asthma, and low levels were also correlated with more severe asthma attacks (8).

Bone weakness and muscle pain

Vitamin D deficiency can result in general muscle pain in both adults and children.

Discover your vitamin D status today, and work with a functional medicine provider to develop a simple, easy-to-follow treatment plan.

Vitamin D Levels

Each person’s individual vitamin D absorption varies significantly, but the Vitamin D Society recommends maintaining optimal vitamin D levels from 100-150 nmol/L. They also determined that levels below 80 nmol/L are “not adequate for any body system” (9).

Currently, the National Institutes for Health (NIH) state that a serum concentration of greater than or equal to 50 nmol/L is generally adequate for most healthy individuals (10). 

The best way to find out the truth about your specific vitamin D status is by getting your levels tested and speaking with an integrative medicine provider about an individualized plan.

Risk Factors for Vitamin D Deficiency

Dark skin. Melanin in skin doesn’t absorb as much UV radiation, which inhibits the synthesis of vitamin D from cholesterol in the skin.

Age. As we age, our skin becomes less efficient at making vitamin D from the sun.

Location. If you live in a country with little sunlight, or if it’s too hot to spend time outside during the summer, you could become vitamin D deficient over time.

Diets low in fish and animal products, dairy.

Indoor lifestyle. With screen use showing no sign of decreasing, we spend more time inside, and less time outside during sunny months when we historically were exposed to more vitamin-D-synthesizing sunlight. 

Obesity. Studies have shown a correlation with low serum vitamin D levels and obesity (3).

Malabsorption due to digestive diseases such as Crohn’s, celiac, IBD, or IBS, etc.

How to Get More Vitamin DVitamin D and immune health

Vitamin D Foods

To get more vitamin D from foods, eat more:

  • Egg yolks
  • Fish (salmon, tuna, mackerel)
  • Fortified dairy and cheese
  • Cod liver oil
  • Mushrooms


The easiest, least expensive way for us to get more vitamin D is to simply spend time outside. In the summer, do this responsibly in places where temperature allows (i.e. 10-15 minute intervals are adequate, be mindful of prolonged heat exposure and the risk of sunburn). 

Vitamin D Supplement

A high-quality D3 supplement can be a good way to bridge the gap of vitamin D deficiency if you’re not able to spend time in the sunlight, or if you don’t regularly consume vitamin D rich foods. 

Opt for a vitamin D3 supplement if available, instead of D2. D2, once thought to be as potent as vitamin D3, is actually only about 50-60% effective as vitamin D3, and that’s assuming optimal kidney function.

You can find D3 in liquid, softgels, or gummies in the CentreSpringMD shop.

Functional Medicine and Vitamin D

Integrative medicine supports the use of vitamin D in the pursuit of optimal health, and the functional benefits it provides. The growing prevalence of vitamin D deficiency affects not only patients with established risk factors, but those who have no risk factors and marginal insufficiency as well.

Schedule an appointment with a CentreSpringMD provider today to optimize YOUR vitamin D status.





Fertility, hair loss, Immunity, Vitamin D

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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any diseases.
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