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Relationship Between Low Vitamin D and Hypothyroidism

A look at how low vitamin D levels impact hypothyroidism and Hashimoto's.
Relationship Between Low Vitamin D and Hypothyroidism
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In this article:

  • What is vitamin D?
  • What does vitamin D do for the body?
  • Does vitamin D cause thyroid disease?
  • Vitamina D and autoimmunity
  • How much vitamin D do I need?

Nearly one-fifth of the world’s population is deficient in vitamin D. For the estimated 20 million people in America with hypothyroidism, optimizing your thyroid function relies heavily on your body receiving the nutrients it needs. Your thyroid gland and overall health can suffer when you are deficient in vital nutrients like zinc, iron, iodine, or vitamin D

What is vitamin D?

Vitamin D is an essential nutrient that our body requires for optimal functioning. Sometimes called the “sunshine vitamin,” vitamin D can be synthesized in our skin when we are in sunlight. This fat-soluble vitamin occurs naturally in very few foods, but we can take it in supplemental form. Because dietary vitamin D can be hard to come by naturally, many foods are fortified with this essential nutrient. 

Dietary sources of natural and fortified vitamin D include:

  • Fish (salmon, trout, cod liver oil, sardines, tuna)
  • Fortified milk, yogurt, and cheese
  • Fortified almond, soy, and oat milk
  • Eggs (especially the yolks)
  • Raw mushrooms
  • Fortified orange juice
  • Fortified cereals and grains

While fortified foods can help boost vitamin D levels, sun exposure is our primary source of vitamin D. Unfortunately, people get less and less sun exposure for a variety of reasons, including less time spent outdoors, increased use of sun protectant, and higher levels of pollution. These factors, and many more, have contributed to an increase in vitamin D deficiencies. Indeed, vitamin D deficiency is sometimes viewed as a global epidemic, affecting over one billion people

What does vitamin D do for the body?

Vitamin D plays several crucial roles in our bodies. It regulates over 200 different genes and is vital for healthy growth and development. Perhaps its most significant roles include promoting calcium and phosphorous absorption from our diet and maintaining a healthy immune system. By increasing calcium and phosphorous absorption from the foods that we eat, vitamin D helps limit the breakdown of our bones and prevents diseases like osteomalacia and osteoporosis. Similarly, healthy levels of vitamin D keep your immune system regulated by preventing inflammation and autoimmune destruction. 

When we are deficient in vitamin D, multiple systems in our bodies can be affected. People with vitamin D deficiency may feel fatigued, depressed, or suffer from muscle, joint, or bone pain. Often, vitamin D deficiency links to other health conditions and diseases, including: 

  • Cancer 
  • Neuropathy
  • Infertility
  • Kidney disease
  • Cardiovascular disease
  • Diabetes
  • Autoimmune disorders including rheumatoid arthritis, lupus, inflammatory bowel disease, multiple sclerosis, and autoimmune thyroid disease

Certain groups of people are at a higher risk for vitamin D deficiency. For example, people with darker skin may have a harder time absorbing vitamin D from sunlight. Older adults lose their ability to efficiently synthesize vitamin D in their skin and convert it through their kidneys. Finally, people with gastrointestinal disorders that impact fat absorption, such as Crohn’s disease, inflammatory bowel disease, and obesity, may have difficulty absorbing vitamin D.  

Does vitamin D cause thyroid disease?

There is no quick answer to this question.

Research indicates that vitamin D may play a role in hypothyroidism and Hashimoto’s thyroiditis. Some studies find that people with Hashimoto’s and non-autoimmune hypothyroidism have low serum blood levels of vitamin D and calcium. This finding may not be that surprising as over one billion people are low in vitamin D. However, evidence suggests that taking a vitamin D supplement may improve serum TSH levels. This improvement in TSH may indicate that vitamin D supplements may decrease the severity of thyroid dysfunction. However, some clinical studies have shown that while TSH levels improved in people taking vitamin D supplements, T3 and T4 levels were not affected.  

There are a few possible explanations for why people with hypothyroidism have low vitamin D levels. Firstly, the intestinal absorption of vitamin D from foods and supplements may be inadequate. Secondly, people with hypothyroidism may not effectively activate vitamin D. Finally, some side effects of hypothyroidism may cause low vitamin D. For example, people with hypothyroidism may spend less time outside in the sun because they are have fatigue or low energy. 

While there appears to be a positive correlation between vitamin D deficiency and hypothyroidism, we do not know if low vitamin D levels cause thyroid dysfunction or if it is a side effect of thyroid disease. 

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Vitamin D and autoimmunity

Vitamin D has anti-inflammatory, anti-oxidant, and anti-fibrotic properties, and it also helps to modulate the immune system. Autoimmunity is when the immune system goes into "overdrive" and attacks its own healthy cells and tissues - such is the case with Hashimoto's disease against the thyroid gland. However, the underlying mechanisms by which vitamin D impacts autoimmune disease remain unclear. Research is also uncertain whether vitamin D deficiency triggers autoimmunity or whether it is a marker of disease progression and severity.

Research suggests that 70% of our immune system resides in our gut, so it's essential to keep her health with a nutrient-rich diet, regular movement, and proper sleep hygiene. For those with a genetic predisposition to autoimmunity, it may be helpful also to address intestinal permeability - a.k.a leaky gut. Leaky gut is when toxins, antigens, and bacteria enter your bloodstream through a weakened intestinal lining. For those who have a family history of Hashimoto's, a leaky gut might trigger or worsen their condition. 

The development and function of the intestinal barrier depend on healthy bacteria in your gut—a.k.a. the microbiota. Things like diet, infections, alcohol, or stress can disturb the gut microbiota and the intestinal barrier function. The good news is that you can heal leaky gut by removing potential triggers, replacing them with nutrients, and supplementing with prebiotics and probiotics. 

There is some evidence that vitamin D might help regulate homeostasis in the gut, which may have a positive effect on your autoimmune symptoms.

How much vitamin D do I need?

The best way to determine if you need to increase your vitamin D intake is to take an essential vitamin blood test. If your blood test reveals that your vitamin D levels are extremely low, it is generally recommended to take a vitamin D supplement and increase your intake of foods high in vitamin D.

According to the National Institute of Health, the recommended daily intake for adults ages 19-70 is 600 IU (or 15 mcg). Adults who are 71 and older should take 800 IU (or 20mcg). These recommendations are for people who do not show signs of vitamin D deficiency. People with vitamin D deficiency or health conditions that may be worsened by low vitamin D should increase their intake based on their doctor’s recommendation. The daily upper limit of vitamin D supplements is 4,000 IU (or 100mcg). 

Toxicity from too much vitamin D is rare, although it can occur in people who take too many vitamin D supplements. It is not possible to get vitamin D toxicity from excess sun exposure because your body limits how much vitamin D it makes from ultraviolet light. 

For people with hypothyroidism, the recommended intake of vitamin D is very individualized. Therefore, it is recommended to meet with a doctor who will help you to figure this out.

A note from Paloma Health

Each of us is unique with individual sensitivities. Work with a physician to create an individualized and comprehensive treatment plan to help you feel your best.

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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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