Vitamin D is an important vitamin that not only regulates calcium, but also has many other beneficial actions. Not many endocrinologists realize this, but several articles published over 20 years ago showed that patients with hypothyroidism have low levels of vitamin D.
This may lead to some of the bone problems related to hypothyroidism. It was thought that one of two mechanisms may explain the low levels of vitamin D in patients with hypothyroidism, 1) the low levels of vitamin D may be due to poor absorption of vitamin D from the intestine or 2) the body may not activate vitamin D properly. Other articles have demonstrated that patients with Graves disease also have low levels of Vitamin D.
Importantly, both vitamin D and thyroid hormone bind to similar receptors called steroid hormone receptors. A different gene in the Vitamin D receptor was shown to predispose people to autoimmune thyroid disease including Graves’ disease and Hashimoto’s thyroiditis. For these reasons, it is important for patients with thyroid problems to understand how the vitamin D system works.
Sources of Vitamin D
Vitamin D is really two different compounds, ergocalciferol (vitamin D2), found mainly in plants and cholecalciferol (vitamin D3), found mainly in animals. Both of these hormones are collectively referred to as vitamin D, and they can either be obtained in two ways. One is by exposure of the skin to the ultraviolet (UV) rays of sunlight or also from dietary intake.
Vitamin D is found naturally in fish (such as salmon and sardines) and fish oils, eggs and cod liver oil. However most Vitamin D is obtained from foods fortified with Vitamin D, especially milk and orange juice. Interestingly, as breast feeding has become more popular, the incidence of Vitamin D deficiency has increased as less fortified milk is consumed.
Vitamin D deficiency may also occur in patients with malabsorption from their intestine, such as in the autoimmune disease called Celiac Disease, which occurs frequently in patients with thyroid problems. Multivitamins also contain Vitamin D, as does some calcium supplements like Oscal-D and Citracal plus D.