Nutrition Notes

Vitamin D and Autoimmune Thyroiditis: Settling the Controversy

While vitamin D is perhaps best known for its role in bone health and calcium metabolism, it exerts critical immunomodulatory actions throughout the body. Vitamin D receptors (VDRs) are present in various immune cells and play a pivotal role in regulating immune responses. This can impact both the innate and adaptive arms of the immune system. The activation of VDRs can cause many downstream effects; these include the modulation of certain pro-inflammatory cytokines and regulatory T-cell differentiation. This, in turn, may influence immune homeostasis. 

Lower levels of vitamin D have been associated with an increased risk of certain autoimmune conditions, including Graves disease (GD) and rheumatoid arthritis (RA). A clinical study involving 101 individuals with RA investigated the seasonal variation of vitamin D levels among participants. Study results indicate a higher prevalence of vitamin D deficiencies and insufficiencies among those with RA. Deficiencies in vitamin D in this population were associated with increases in parameters related to inflammation and disease activity, including C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). 

A large-scale randomized controlled trial lasting over 5 years and involving over 25,000 participants, primarily older adults, explored the relationship between autoimmune diseases and the intake of vitamin D and omega-3 fatty acids. The intervention involved 2,000 IU of vitamin D daily or a matched placebo and 1,000 mg omega-3 fatty acids or a matched placebo. Results from the study indicate that supplementation with vitamin D, independent of omega-3 intake, was associated with a 22% reduced incidence of autoimmune disease.

A pilot study investigated the potential efficacy of selenium and vitamin D supplementation in individuals (n=42) newly diagnosed with GD with low serum levels of circulating calcifediol and selenium. All participants received medication for GD according to the standard of care. The treatment group also received 100 µg of selenium daily plus an amount of cholecalciferol based on individual baseline serum values for 180 days. 

Study results indicate that individuals receiving vitamin D and selenium may have experienced improvements in certain aspects of immune and thyroid health. The treatment group was observed to have higher amounts of T regulatory (Treg) cells at the study terminus when compared with placebo. Treg cells are responsible for helping to control autoreactive immune cells and may help prevent certain aspects of autoimmune disease progression. In addition, decreases in certain natural killer (NK) cells including CD56brightNK cells were observed in the treatment group. While the full mechanism of NK cell activity in GD is still being elucidated, NK cells are thought to contribute to both the innate and adaptive immune responses, produce certain cytokines, and contribute to immune cell signaling. Certain NK cells, particularly CD56brightNK cells, have been observed in higher amounts in individuals with GD when compared to healthy volunteers. 

While more research is needed, particularly in the clinical setting and with more study participants, evidence suggests that certain nutraceuticals may help support thyroid health and a normal immune response. Emerging evidence suggests that supplementation with vitamin D may help support antioxidative status, immune health, and a normal response to inflammation. 

By Cory Ambrose, ND, MAT