Article - The Effect of Vitamin D Supplementation on Thyroid Hormone Levels in Patients With Autoimmune Thyroid Disease: A Systematic Review.

Plain Language Summary

In clinical practice, thyroid disorders, especially autoimmune thyroid diseases (AITDs), are one of the most predominant endocrine abnormalities, and they are the most common pathological condition of the thyroid gland. This study aimed to systematically assess how vitamin D administration affected thyroid function tests, namely, thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4) in patients with AITDs. This research was a systematic review of seven studies. Results showed that the effect of vitamin D on thyroid function appears to vary significantly across different studies. Only three of the included studies demonstrated significant changes in TSH levels. Additionally, the influence of vitamin D on T3 levels exhibited significant changes in two studies, while the changes in T4 levels were consistent with TSH. Authors concluded that their findings are in agreement with other studies, which also show varying responses to vitamin D supplementation.

Expert Review

Reviewer: Karin Elgar

6th Feb 2025

Conflict of interest

None

Take home message

Vitamin D supplementation may support thyroid hormone regulation in patients with AITD and low levels of vitamin D when used for at least 6 months.

Evidence category

B: Systematic reviews including RCTs of limited number

Summary review

Introduction

Observational research has shown that low vitamin D levels are associated with autoimmune thyroid diseases (AITD), which include Hashimoto’s thyroiditis and Graves’ disease.
The aim of this systematic review was to evaluate the effects of vitamin D supplementation on thyroid hormone levels in patients with AITD.

Methods

This is a systematic review searching PubMed, Medline, PubMed Central, Cochrane Library, and ScienceDirect.
Inclusion criteria: Randomised clinical trial, adults with AITD, vitamin D supplementation at any dose and route of administration, at least one thyroid hormone assessed (thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) or thyroxine (T4)), free full access articles written in English within the last 10 years.
Cochrane Risk-of-Bias (RoB) tool used for quality assessment of included studies.

Results

7 Trials met the eligibility criteria including a total of 516 patients.
None of the studies had an overall high risk of bias.
All studies were conducted in Asia and participants had low mean baseline vitamin D levels.
Dose of daily supplementation ranged from 800-1200 IU (3 trials), dose of weekly supplementation was either 50,000 IU (2 trials) or 60,000 IU (2 trials). Duration of supplementation ranged from 1-12 months.
There was no significant change in thyroid hormones in studies lasting 3 months or less.
TSH, T3 and T4 improved significantly in studies lasting 6 months or more: TSH (p=0.000 – <0.001, compared to control n=2, p=0.001 compared to baseline n=1); T3 (p=0.000 – 0.001, , compared to control n=2); T4 (p=0.000 – <0.001, , compared to control n=2, p=0.005 compared to baseline n=1).

Conclusion

The authors concluded that vitamin D supplementation may contribute to thyroid hormone regulation in AITD.
Limitations of the reviewed studies included small sample sizes and short duration of supplementation.

Clinical practice applications

Vitamin D supplementation for at least 6 months may support thyroid hormone regulation in patients with AITD and low vitamin D levels.

Considerations for future research

Larger studies of vitamin D supplementation with higher dose and/or longer durations to establish optimal dosing regimen.
Clinical studies in other geographical locations/other ethnic populations to increase generalisability.

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Abstract

Autoimmune thyroid diseases (AITDs) pose significant challenges in clinical practice, representing one of the most common endocrine abnormalities. Vitamin D deficiency has been linked as one of the contributing factors to the etiology of AITDs. This systematic review evaluates the effects of vitamin D supplementation on thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels in adults with AITDs. Using a PICO (population, intervention, comparison, and outcome) framework and adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, seven relevant studies were identified from an initial pool of 1,469 articles. The population comprised individuals with thyroid autoimmunity, as evidenced by at least one elevated positive thyroid autoimmune marker and intervention involved the supplementation of vitamin D, regardless of the dose or method of administration. All randomized clinical trials within the last 10 years, which fit the study criteria, were included. These studies showed varying results based on follow-up duration. Short-term studies (three months or less) demonstrated no significant changes in mean TSH, T3, or T4 levels compared to the control group with vitamin D supplementation. However, all of the long-term studies (greater than three months) indicated significant improvements compared to the control in mean TSH, T3, and T4 levels. Additionally, all long-term studies that compared TSH, T3, and T4 to baseline levels revealed significant changes by the trial's end. Despite these promising findings, the review highlights limitations, including small sample sizes, short study durations, and the need for further research to establish optimal dosing and treatment duration for vitamin D in AITD management. The overall findings suggest that vitamin D supplementation may play a part in thyroid hormone regulation in AITD, particularly with prolonged administration.