Effects of vitamin D supplementation on autoantibodies and thyroid function in patients with Hashimoto's thyroiditis: A systematic review and meta-analysis.

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Regular monitoring of vitamin D levels in patients with Hashimoto’s Thyroiditis is recommended to prevent exacerbation of their symptoms and condition. Ideally, this should be carried out by a qualified healthcare professional.

Introduction

A higher prevalence of vitamin D insufficiency or deficiency has been found in people with Hashimoto’s Thyroiditis (HT). This may be a contributing factor to the aetiology of HT due to vitamin D’s regulatory role on the immune system. Supplementation with 25-hydroxyvitamin D (25(OH)D) may improve thyroid function and reduce thyroid antibodies, however, there is conflicting evidence. The aim of this study was to evaluate the efficacy of 25(OH)D supplementation for improving HT based on a meta-analysis of randomised controlled trials (RCTs).

Methods

• 12 RCTs were included with a total population of n=862. Patients were diagnosed with either HT, subclinical hypothyroidism or euthyroid.
• N=429 were allocated to treatment groups and N=423 to control groups. Treatment included calcitriol (6 studies) or vitamin D3 (1 study), alongside thyroxine treatment, or 25(OH)D exclusively if euthyroid or subclinical hypothyroid (2 studies D2, 1 study D3, 2 studies calcitriol). Control groups were given a placebo or no treatment. Study durations ranged from 12-24 weeks.
• Baseline and end of study measurements included: 25(OH)D, thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), anti-thyroid peroxidase antibody (TPO-Ab), and thyroglobulin antibody (TG-Ab).
• Subgroup analyses included study duration (> or < 12wk), type of 25(OH)D supplementation, baseline thyroid function (HT, Subclinical hypothyroid, euthyroid). Baseline vitamin D levels (deficient, insufficiency, indeterminant).

Results

• TSH levels were reduced following 25(OH)D supplementation in patients with HT (SMD =-0.167, 95% CI).
• Increases in FT4 (p=<0.009, SMD=0.734, 95% CI) and FT3 (p=<0.02, SMD =0.549, 95% CI) were observed in 10/12 studies in patients with HT with greater reductions in treatment durations >12 weeks (p=<0.05).
• A reduction in TG-Ab (assessed in 11/12 studies) compared to control groups in patients with HT (p=0.001, SMD =-0.996, 95% CI) was consistently reported in 9/12 studies.
• Calcitriol was more effective than naïve 25(OH)D (p=<0.001, SMD -1.522, 95% CI) for reducing TPO-Ab in HT patients. Greater reductions were observed in studies of >12 weeks in duration.

Conclusion

25(OH)D Supplementation may be beneficial for improving thyroid function and modulating immune responses in people with HT. Further prospective studies with large and diverse populations are needed to confirm these results.

• 25(OH)D supplementation for >12 weeks may lower TSH and increase FT3 and FT4 and in people with HT. However, baseline thyroid function may be a significant factor affecting the FT3 results. Treatment duration >12 weeks led to more significant increases in FT4 and FT3.
• A decrease in antibodies TPO-Ab and TG-Ab, was found regardless of baseline thyroid function. A treatment duration >12 weeks further improved TPO-Ab levels and calcitriol had a more pronounced effect (p=<0.001) compared to vitamin D2 or D3. However, the safety of calcitriol for HT requires further investigation due to an increased risk of hypercalcemia.
• Clients with hyperthyroidism or hypothyroidism may benefit from receiving 25(OH)D supplementation of 1500 to 2000 IU/d to prevent a deficiency from exacerbating their condition. Regular monitoring (serum/urine) for calcium is recommended.

• Further prospective studies with longer durations and larger populations are needed. These should also consider, racial diversity (10 studies were in China and 2 in Iran), somatotype variations, environmental variables, baseline thyroid function, vitamin D levels, dosage and duration of vitamin D treatment and L-4 dosage.
• Further research into the safety of calcitriol as an HT intervention are needed.