Vitamin D and Thyroid Health

Vitamin D and Thyroid Health

The idea of vitamin D supplementation has been promoted for a long time as a possible fix for bone and immune system health, depression, diabetes, and many other conditions. This trend has led to the rapid development of the supplement market. According to a recent CDC report, approximately 45% of middle-aged women and 38% of middle-aged men report taking a vitamin D supplement, and hundreds of thousands of Americans get tested for vitamin D deficiency each year. In this article, we will discuss the connection between vitamin D levels and thyroid diseases.

Autoimmune Thyroid Disorders

Researchers have generally accepted the association between low serum vitamin D and autoimmune thyroid disorders. The latest review concludes that although there is some inconsistency in the studies’ results, most of the data confirms the association between lower vitamin D levels and increased risk of developing autoimmune thyroid disease. The authors suggest that vitamin D plays a small yet significant role in the disease’s pathogenesis, which may only be apparent when other factors that contribute to its expression are present. Another important conclusion of this study is that there is a lack of data establishing the exemption from harm and the presence of benefit of obtaining high levels of 25(OH)D. Therefore, it is recommended to aim for a 25(OH)D level within the reference ranges without aiming to go above them.


Multiple studies indicate that hypothyroid patients are likely to be vitamin D deficient, but up to date, it is not clear whether one of these conditions causes another. Some studies conclude that low serum vitamin D and calcium levels are significantly associated with the degree and severity of hypothyroidism observed in patients. Besides, some symptoms such as fatigue, lack of concentration, hair loss can be present in both diseases and complicate the diagnostic process. Thus, vitamin D deficiency screening often comes in handy in the process of hypothyroidism diagnostics.

Thyroid Cancer

Another review has addressed the possible connections between vitamin D deficiency and thyroid cancer. Both in vitro models and in vivo animal models have demonstrated that vitamin D has anti-proliferative, pro-differentiative, pro-apoptotic, and anti-inflammatory actions within the tumor microenvironment. However, according to the British Thyroid Foundation, it remains unclear whether low vitamin D level is a cause, a consequence, or an innocent bystander in developing common thyroid conditions such as thyroid cancer. It is possible that vitamin D deficiency may cause an under-performing immune system to facilitate thyroid disease progression. Alternatively, it is also possible that people with thyroid diseases may have altered health or lifestyle, leading to a low vitamin D state. For example, patients with an underactive thyroid may spend less time outdoors due to tiredness and thus have reduced sun exposure. Therefore, more research is needed to determine the role of vitamin D in the treatment and prevention of thyroid diseases.

Despite such an unsolid ground in thyroid disease treatment, the National Institutes of Health recommends all adults (19–70 years) to obtain 15 mcg (600 IU) of vitamin D daily. Keep in mind that it should not come from the supplement only – time outdoors, certain products such as fatty fish, liver, egg yolks, and a variety of artificially fortified products can also be your primary source of vitamin D. Even though vitamin D supplement is available in various concentrations, it is not recommended to take doses higher than 100 mcg (4,000 IU) per day without doctor’s prescription. The signs of vitamin D overdose include nausea and vomiting, weakness, stomach pain, constipation, and frequent urination. Vitamin D toxicity might progress to bone pain and kidney problems, such as the formation of calcium stones and even renal failure. Vitamin D toxicity almost always occurs from the overuse of supplements. Interestingly, excessive sun exposure doesn’t cause vitamin D toxicity because the body limits the amount of the vitamin it produces.

You can track your vitamin D levels with the help of ThyForLife, as well as hundreds of other bloodwork parameters. You may also set up reminders not to forget about your daily supplement or annual check-up.


At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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