Vitamin D, a fat-soluble vitamin that functions like a hormone or steroid, appears to have the most beneficial effect on the immune system as it relates to thyroid health, rather than any direct effect on the thyroid gland itself.
This makes it a viable therapeutic option for treating thyroid autoimmunity, such as Hashimoto’s and Graves’ disease.
An optimal vitamin D concentration can be achieved through both sun exposure and supplementation, relying more on supplements during the winter months.
The effect of vitamin D on the thyroid gland is a little bit tricky to understand. The research on the relationship between this fat-soluble vitamin and a healthy thyroid (euthyroid) is somewhat mixed in terms of its efficacy.
On the one hand, vitamin D deficiency can certainly contribute to thyroid problems, and disease in general. Low vitamin D levels are also linked to increased risk of thyroid autoimmunity. But vitamin D supplementation does not seem to impact thyroid function or parathyroid hormone output, including TSH (thyroid-stimulating hormone), thyroxine (T4), or T3 levels.
In this article, we’ll dig into the benefits of vitamin D for thyroid health, whether you should supplement, evaluating sun exposure for vitamin D production in the skin, and the research behind vitamin D and thyroid autoimmunity.
What Is Vitamin D and Why Should We Care About It?
Vitamin D is a fat-soluble vitamin with hormone-like effects, and it has many key functions in the body. It plays an important role in bone health, regulation of calcium and phosphorus levels, and immune system modulation [1, 2].
Vitamin D is sometimes referred to as the “sunshine vitamin” because it’s produced in the skin during sun exposure .
In terms of thyroid health, vitamin D deficiency is associated with hypothyroidism, Hashimoto’s thyroiditis, hyperthyroidism, and Graves’ disease, as well as many other forms of autoimmune disease.
Low vitamin D is a risk factor for or associated with numerous other chronic conditions, including other autoimmune diseases like type 1 diabetes and multiple sclerosis, as well as other conditions like cardiovascular disease and obesity.
Low vitamin D is also associated with low mood and brain function. It may be a root cause of seasonal affective disorder, where some people become depressed during the winter months without adequate sun exposure.
The Role of Vitamin D in the Body
Vitamin D plays the following roles in the body:
Alters gene expression
Increases calcium and phosphorus levels by stimulating absorption in the intestines
Stimulates reabsorption of calcium in the kidneys
Stimulates insulin production
Modulates the function of immune cells
Reduces the production of certain pro-inflammatory cytokines
Has beneficial effects on certain skin conditions.
As you can see, there are many reasons to ensure that you have enough vitamin D in your body, including but not limited to thyroid health.
Forms of Vitamin D
Vitamin D2 (also called ergocalciferol) is the form found in plants. It’s not biologically active and when ingested, our bodies have to convert it to D3 (also called cholecalciferol). Vitamin D3 is the most common form of vitamin D in the body and is made in the skin from exposure to the sun’s ultraviolet rays (ultraviolet B radiation or UVB) .
You may also see serum 25-hydroxyvitamin D or 25-(OH)D (also called calcidiol) on blood tests for serum vitamin D levels. This form is what you get when D3 undergoes conversion in the liver, and it has a longer half life of two to three weeks, making it easier to measure in the blood .
What Is the Relationship Between Vitamin D and Thyroid Health?
Low vitamin D levels have been clearly tied to thyroid disease, especially hypothyroidism, thyroid autoimmunity, and thyroid cancer.
Instead of directly affecting thyroid hormone output, Vitamin D appears to influence thyroid health indirectly by modulating the immune system.
One literature review stated that vitamin D inhibits Th17 cells (which are involved in autoimmunity) and promotes regulatory T cells (which help suppress autoimmunity) .
Additionally, another 2022 literature review concluded that vitamin D has anti-inflammatory effects and can prevent an overexaggerated immune response(i.e. autoimmunity) .
Vitamin D and Thyroid Autoimmunity
When we look at autoimmune thyroiditis or Hashimoto’s disease, the connections between vitamin D deficiency and manifestation of these diseases are strongly correlated.
A 2021 systematic review and meta-analysis of 42 observational studies attempted to explore the relationship between vitamin D and autoimmune thyroid disease (AITD).
A total of 12,916 participants (1,886 with AITD) were analyzed and the results showed that subjects with AITD, Hashimoto’s thyroiditis, and hypothyroidism had significantly lower levels of vitamin D compared to the control group .
This is just one of many studies showing a correlation between low vitamin D levels and thyroid autoimmunity. Many studies also showed that people who were more deficient in vitamin D had higher thyroid antibodies and thyroid autoantibodies, including TG (TGAb) and TPO antibodies (TPOAb).
Supplementing Vitamin D for Thyroid Health
There are mixed results in using vitamin D specifically for thyroid hormone regulation. Rather, the primary benefit of vitamin D supplementation on thyroid health appears to be its favorable effect on the immune system.
Long-term supplementation of vitamin D3 has shown to reduce the overall incidence of autoimmune disease , and several studies have shown that vitamin D improves thyroid autoimmunity.
Several high-quality studies have shown that vitamin D supplementation can significantly decrease (improve) TPO antibody levels.
A recent review found thatvitamin D supplementation decreased TPO antibody levels by about 158 (a very significant improvement) , while another study found that supplementation with vitamin D3 for more than three months significantly improved TPO antibody levels . A third study found that vitamin D significantly decreased TPO antibody levels after six months .
Additionally, one clinical trial found that taking vitamin D with selenium was more effective at reducing TPO antibodies than vitamin D alone , and another study found that taking vitamin D with the hormone DHEA was more effective for reducing TPO antibody levels than taking vitamin D alone .
If you’re interested in using vitamin D as part of a thyroid autoimmune protocol, consult with your doctor for appropriate testing and dosage.
What Are the Main Signs You Have Low Vitamin D Levels?
The prevalence of vitamin D deficiency (also called hypovitaminosis D) and insufficiency is unfortunately quite common. Although education around the importance of vitamin D has grown in recent years, it’s still estimated that one billion people are deficient, and 50% of the population has insufficient vitamin D levels [1, 3].
Blood levels of vitamin D below 30 ng/mL are considered to be deficient, according to the Endocrine Society, the National and International Osteoporosis Foundation, and the American Geriatric Society.
The recommended range is between 40 and 60 ng/mL for the average person. But each individual is different, and a good vitamin D status may go as high as 80 ng/mL for a person with a history of cancer and/or chronic disease.
If you suspect you have low vitamin D, you can easily determine your vitamin D level with a standard blood test and supplement and/or increase synthesis with sun exposure based on the results.
How to Get More Vitamin D: Supplements or the Sun?
On my podcast, I was able to sit down with Dr. Michael Holick, a functional medicine doctor who specializes in sun exposure and vitamin D testing and treatment.
Dr. Holick recommends that everyone get adequate sun exposure during the day. Contrary to popular belief, we don’t need to be afraid of the sun as long as we’re not burning the skin. Sun exposure is actually essential for health and longevity.
Of course, a big reason for this is that you get the best form of vitamin D from sun exposure on your skin. A light pinkness to the skin after a day in the sun is called a minimal erythemal dose, and translates to 20,000 IUs of vitamin D!
Sunlight also produces beta endorphin, which is what makes people feel good when they’re out in the sunlight. You may also feel more relaxed by producing nitric oxide, which lowers blood pressure.
Dr. Holick recommends both sun exposure and vitamin D supplementation to keep our levels within optimum range. The base recommendation for vitamin D supplementation is 5,000-6,000 IUs per day, along with non-burning sun exposure.
What’s “adequate” sun exposure for you will depend on many factors: time of day, time of year/season, skin pigmentation, and more. You can track your vitamin D production from the sun using the dminder app, which allows you to input time of day, season, latitude, and other factors that affect vitamin D production.
During the winter, you should be able to maintain your vitamin D levels with a 5,000 IU vitamin D supplement without as much sun exposure.
To get the most out of your vitamin D supplement, take it with a source of healthy dietary fat, as vitamin D is fat-soluble. Taking it with fat will increase bioavailability, helping your body absorb and use it better.
Optimal Vitamin D and Thyroid Health Go Hand in Hand
Though it may not have a direct effect on thyroid or thyroid hormones, having an optimal vitamin D level can protect you from thyroid disorders as well as improve markers of thyroid autoimmunity.
It’s important to get some combination of vitamin D from supplements and sun exposure, especially during the summer months while the sun is the most therapeutic. Just don’t stay out too long and get sunburned.
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