Vitamin D and Hashimoto's thyroiditis

Relation

Chahardoli R, Saboor-Yaraghi AA, Amouzegar A, Khalili D, Vakili AZ, Azizi F. Can vitamin D supplementation alter thyroid autoantibodies (anti-TPO Ab, anti-Tg Ab) and thyroid profile (T3, T4, TSH) in Hashimoto's thyroid? A double-blind, randomized clinical trial.Horm Metab Res. 2019;51(5):296-301.

Draft

Randomized, double-blind, placebo-controlled clinical trial.

Participant

The study included 42 women ages 18 to 48 with Hashimoto's thyroiditis. All participants were treated with levothyroxine for hypothyroidism. Exclusion criteria were immune system diseases, liver dysfunction, malnutrition, body mass index (BMI) 40, and other autoimmune diseases, including type 1 diabetes, inflammatory bowel disease, and multiple sclerosis. Women who had taken vitamin D, vitamin A, or omega-3 fatty acid supplements in the past 6 months were also excluded from the study.

Study parameters assessed

The participants were randomly divided into 2 groups. One group received 50,000 IU of vitamin D beads orally per week for 3 months. The other group received a placebo bead made from edible paraffin oil.

At the beginning and end of the study, researchers measured serum levels of TSH (thyroid stimulating hormone), T₄(left-handed thyroxine), T₃(triiodothyronine), 25-hydroxy-vitamin D [25(OH)D], calcium, antithyroglobulin antibodies (anti-Tg-Ab) and antithyroperoxidase antibodies (anti-TPO-Ab). They also assessed sun exposure (in hours/day) and dietary vitamin D intake (via dietary records) at the beginning and end of the study.

Primary outcome measures

The primary endpoints were any changes observed in the blood tests mentioned above.

Key insights

After 3 months of supplementation, the vitamin D group had increased serum levels of vitamin D and calcium. During the course of the study there was a significant reduction in anti-Tg Abs and TSH. There were no significant changes in anti-TPO Ab levels in the vitamin D group compared to placebo. No significant changes in T₃or T₄levels occurred in both groups.

Practice implications

This is the latest of several studies that have shown that vitamin D may have an impact on Hashimoto's thyroiditis.^1.2In addition to the well-known effects of vitamin D on calcium metabolism, vitamin D plays an essential role in the regulation of the immune system.²This study further highlights their potential to modify the course of autoimmunity, particularly in relation to the thyroid.³

Vitamin D receptors are found in lymphocytes, macrophages and antigen-presenting cells.⁴1-alpha-hydroxylase, which is found in antigen-presenting cells, is also necessary to convert vitamin D into its active form. Vitamin D also downregulates the production of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) and reduces T cell proliferation. Nettore et al. find that innate immunity is enhanced and the acquired immune response (as found in Hashimoto's thyroiditis) is suppressed in the presence of vitamin D.⁴

Regardless of the specific cause and effect, reduced autoimmune response is generally associated in the literature with higher vitamin D levels.

Antibodies found in autoimmune thyroid diseases include TPO antibodies and Tg antibodies. TPO is an enzyme that facilitates the synthesis of T₄and T₃. Anti-TPO Ab increase the production of TNF-α and interferon-gamma (IFN-γ). As mentioned above, vitamin D has been shown to inhibit these inflammatory cytokines.

Tg is a glycoprotein found in the thyroid gland, where thyroid hormones are synthesized. An increase in anti-Tg Abs is associated with an upregulated Th1 and Th2 response. Here too, vitamin D suppresses these reactions. In this study, the effect of vitamin D on anti-Tg Abs was more pronounced than on anti-TPO Abs. Other studies have found a greater impact on anti-TPO Abs,^5.6and another study theorized that increased thyroid antibodies cause a decrease in systemic vitamin D.⁷Regardless of the specific cause and effect, reduced autoimmune response is generally associated in the literature with higher vitamin D levels.

It's important to remember that vitamin D is not the only nutrient that plays a role in maintaining and restoring thyroid health. In addition to the obvious substrates for thyroid hormone production (iodine and tyrosine), selenium helps reduce antibody titers in Hashimoto's thyroiditis.⁸Accordingly, the combination of selenomethionine together with vitamin D therapy increased the overall effectiveness of the therapy.⁶

With this in mind, when we look at the role of vitamin D in the treatment of Hashimoto's thyroid disease, it is useful to remember that its mechanism likely lies in the modification of the immune response. In the study reviewed here, there was some change in TSH and thyroid hormone production, but the main benefit was seen in the reduction of antibodies. Vitamin D is just one part of a treatment protocol that addresses the whole person. Strategic therapies to reduce the initiation of the autoimmune response, to improve the production of T₄and T₃and optimize the conversion of T₄to T₃is necessary. Addressing stressors, other endocrine imbalances, metabolism, environmental influences, etc. is also a critical part of a holistic approach to autoimmune thyroid disease.