The impact of vitamin D status and supplementation on thyroid autoimmunity

Background. In spite of large volume of data linking vitamin D (VD) with cardiovascular morbidity, autoimmunity, cancer, and virtually every organ system, VD and thyroid is a lesser-known aspect of VD in clinical practice. The reason for this almost ubiquitous role of VD is perhaps because VD receptor (VDR) is virtually expressed in every tissue and organ system of the body. This review intends to highlight the current literature on the impact of VD status and supplementation on thyroid autoimmunity. Materials and methods. References for this review were identified through searches of PubMed for articles published to from 2015 to September 2020 using the terms “thyroid” and “Vitamin D”. Results. Significant inverse correlation was documented between anti-thyroid peroxidase antibody (TPO Ab) and serum 25-hydroxyvitamin D 25(OH)D. TPO Ab positivity is more prevalent in VD deficient individuals. A large volume of medical literature is available from observational studies linking VD with thyroid autoimmunity. Data from interventional studies documenting beneficial effects of VD on thyroid autoimmunity is also available, but lesser than that from observational studies. Short-term high dose oral VD supplementation reduces TPO Ab titers. Certain VDR gene polymorphism has been linked to increased occurrence of autoimmune thyroid disorders (AITD). Data on whether correction of Vitamin D deficiency in AITD results in reduction in the requirement of levothyroxine or carbimazole in hypothyroidism or Graves’ disease respectively is not available. Conclusions. In spite of large volume of medical literature from observational studies linking VD with thyroid autoimmunity, meaningful concrete clinical data on impact of VD supplementation on hard clinical end points in these disorders is lacking, and should be the primary area of research in the next decade.