According to “The Merck Manual of Diagnosis and Therapy,” Grave’s disease is the most common cause of an overactive thyroid gland, also known as hyperthyroidism. Like other causes of hyperthyroidism, Grave’s disease is characterized by elevated levels of thyroid hormones in your bloodstream, which result in weight loss, tremors, rapid heartbeat, fatigue, accelerated bone turnover and other symptoms. Grave’s disease typically inhibits vitamin D production, and the way you metabolize vitamin D could increase your risk for developing this condition.
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Grave’s disease is an autoimmune disorder, meaning it is caused by your immune system attacking your own tissues. The underlying triggers for this inappropriate immune response have not been identified. In Grave’s disease, antibodies attach to receptors on your thyroid and prompt the excessive release of thyroid hormones, which are stimulatory in nature. Thyroid hormones enhance cellular metabolism of fats, carbohydrates and proteins and increase nervous system activity. Under the influence of thyroid hormones, bone turnover is amplified, which releases calcium into your bloodstream.
Vitamin D Activation
According to the May 2008 issue of the Polish journal “Acta Biochimica Polonica,” the accelerated bone turnover and consequent release of calcium associated with Grave’s disease causes a decrease in synthesis of active vitamin D. Whenever you are exposed to sunlight, you manufacture vitamin D in your skin. Vitamin D is also found in some foods and in supplements. However, all these forms of vitamin D must be activated in your liver and kidneys before they can exert their effects in your tissues. Since activated vitamin D increases your calcium level, your body slows the activation process when calcium concentrations in your bloodstream are already adequate or rising.
Vitamin D Receptors
Nearly every cell in your body possesses vitamin D receptors, or VDRs, which determine how your tissues respond to vitamin D stimulation. VDRs are intimately involved in your immune system’s function. Just like eye color, lip shape and finger length, VDR expression is influenced by a variety of different genes called polymorphisms, meaning “many forms.” Two studies, one conducted in 2005 among Croatian women and another completed in 2009 in both Caucasian and Asian women, demonstrated that certain VDR polymorphisms increase susceptibility to Grave’s disease in Asian and Croatian females.
Grave’s disease is correlated with vitamin D deficiency in several interesting ways. People with Grave’s disease frequently have low vitamin D levels, primarily as a result of increased thyroid hormone production, accelerated bone turnover and decreased vitamin D activation. However, there is apparently a cause-and-effect relationship between vitamin D deficiency and Grave’s disease, in that VDR gene polymorphisms determine how you metabolize vitamin D and how your immune system responds to this nutrient. Better characterization of these relationships may one day help to identify individuals at risk for Grave’s disease and guide their treatment. If you have Grave’s disease, ask your doctor if you need additional vitamin D.