Vitamin D Deficiency and Your Thyroid

Woman wearing sun hat
Aleksandra Jankovic/Stocksy United

Vitamin D's main role is to regulate bone metabolism and calcium and phosphorus levels in the body, so it is not surprising if you generally associate vitamin D with keeping your bones strong and healthy. 

Over the past several years, though, other vitamin D roles have been examined, including its role in heart disease, cancer, and autoimmune conditions, like Hashimoto's and Graves' disease.

Let's delve a bit deeper into the basics of vitamin D, and what a deficiency in this vitamin may mean for your thyroid health.  

Understanding Vitamin D Deficiency

Vitamin D is known as the "sunshine vitamin" because your body makes it after your skin is exposed to ultraviolet rays from the sun. Vitamin D can also be found in certain foods such as: 

  • Fatty fish like salmon, mackerel, tuna, trout, herring, and sardines
  • Cod liver oil
  • Some dairy products (for example, milk, soy milk almond milk, yogurt)
  • Fortified ready-to-eat cereals
  • Fortified orange juice
  • Hard-boiled eggs

A deficiency in vitamin D causes rickets in children and osteomalacia in adults. Rickets is rare now in the United States due to the fortification of milk, but osteomalacia remains a problem, especially due to its subtle symptoms of bone pain and muscle weakness. 

Definition

According to the Institute of Medicine, vitamin D deficiency is defined as a level less than 30 nmol/L, while a vitamin D level greater than or equal to 50 nmol/L is considered sufficient.

People with vitamin D levels between 30 nmol/L and 49 nmol/L are considered at risk for vitamin D deficiency. 

Keep in mind, there is no standard guideline regarding what an "optimal" vitamin D level is for a person with thyroid disease. It's possible that if you have autoimmune thyroid disease, your doctor may want your vitamin D level to be higher than 50 nmol/L, perhaps closer to 75 nmol/L.

Causes

There are multiple potential causes for vitamin D deficiency, but a big one has to do with low sunlight exposure, due in large part to the frequent use of sunblock to prevent skin cancer (a good measure, for sure), and the fact that we spend more time indoors on our phones and computers. 

Diet too is an issue, considering there is not a whole lot of foods that contain vitamin D naturally. Most multivitamins do not contain enough vitamin D either—multivitamins typically have 400 IU vitamin D, but the recommend daily intake is around 600 IU for adults and 800 IU for adults over the age of 70. 

Besides diet and low sunlight exposure, other causes of low vitamin D levels include:

  • Gut malabsorption of vitamin D (for example, celiac disease or Crohn's disease)
  • Increased breakdown of vitamin D (anti-seizure medications)
  • Impaired production of active form of vitamin D  (liver or kidney disease)
  • Decreased skin production of vitamin D (dark-skinned individuals)
  • Sequestration of vitamin D in fatty tissue (obesity)

Diagnosis

Based on the link between vitamin D deficiency and thyroid disease, it's not surprising that many doctors check vitamin D levels for their patients with autoimmune thyroid disease.

The good news is that your vitamin D level can be easily evaluated with a simple blood test, called 25-hydroxy vitamin D. 

Toxicity

As with the vast majority of supplements and vitamins, more vitamin D is not necessarily better. At toxic levels of vitamin D, which is a blood level greater than 125 nmol/L, a person may experience symptoms of high calcium levels (called hypercalcemia), including fatigue, a loss of appetite, constipation, nausea and vomiting, and forgetfulness. Heart arrhythmias and kidney problems may also result from vitamin D toxicity. 

Vitamin D and Your Thyroid

Research has found a link between Vitamin D deficiency and autoimmune thyroid diseases (AITD), which are Hashimoto’s thyroiditis and Graves’ disease.

For example, one study found that the presence of vitamin D deficiency was significantly higher in patients with autoimmune thyroid disease, as compared to healthy patients (72 percent versus 31 percent, respectively).  

Other research has found an association between vitamin D deficiency and the presence of anti-thyroid antibodies, hinting that vitamin D deficiency may be a trigger for the development of autoimmune thyroid disease.

Lastly, early research suggests that vitamin D supplementation may help manage thyroid disease. For instance, one study demonstrated that antibodies in autoimmune thyroid disease significantly decreased as a result of taking vitamin D at 1,000 IU per day for one month.  

The bottom line here is that vitamin D may play a role in a person's thyroid health, but whether or not there is a direct link between vitamin D deficiency and the development or progression of autoimmune thyroid disease remains unknown. 

A Word From Verywell

While the significance of vitamin D for your autoimmune thyroid disease is unclear at this time, checking a vitamin D level is a sensible and easy step, and something your doctor may have already done. If not, it's reasonable to discuss checking a level at your next doctor's visit and supplementing with vitamin D if you are deficient. Of course, be sure to only take vitamin D under the care of your doctor—depending on your level, you may require a unique dosing regimen.

View Article Sources