A new meta-analysis pooled 38 studies to compare vitamin D levels in people with thyroid diseases and people without thyroid disease. The thyroid conditions included Graves' disease, Hashimoto's thyroiditis, and unclassified autoimmune thyroid disease.
Overall, vitamin D levels were significantly lower in people with thyroid disease. The average difference was about 5.4 ng/mL lower than in controls. When broken down by condition, people with Graves' disease had levels about 4.1 ng/mL lower, those with Hashimoto's thyroiditis about 7.5 ng/mL lower, and those with unclassified autoimmune thyroid disease about 2.2 ng/mL lower.
This was a meta-analysis of observational studies, so it shows a link, not cause and effect. It does not prove that low vitamin D causes thyroid disease or that taking vitamin D will help. The analysis did not report side effects, funding sources, or study limitations.
If you have a thyroid condition, talk with your doctor about whether checking your vitamin D level makes sense for you. Do not start or change any supplement on your own based on this finding.
Common questions
Is low vitamin D a cause of thyroid disease?
This analysis cannot say. It pooled observational studies, which can show a link but not prove that low vitamin D causes thyroid disease. It is possible that thyroid disease or other factors lead to lower vitamin D, or that both share a common cause. More research is needed to understand the direction of this relationship.
Which thyroid conditions were linked to lower vitamin D?
The analysis looked at Graves' disease, Hashimoto's thyroiditis, and unclassified autoimmune thyroid disease. All three groups had lower vitamin D levels than people without thyroid disease. The difference was largest for Hashimoto's thyroiditis, about 7.5 ng/mL lower, and smallest for unclassified autoimmune thyroid disease, about 2.2 ng/mL lower.
Should I take vitamin D if I have a thyroid condition?
This analysis did not test whether vitamin D supplements help thyroid disease. It only looked at existing vitamin D levels. Whether to take a supplement is a personal decision. Talk with your doctor, who can check your levels and advise based on your health history and any other conditions or medications.
How much lower was vitamin D in people with thyroid disease?
On average, people with thyroid disease had vitamin D levels about 5.4 ng/mL lower than controls. For Graves' disease, the difference was about 4.1 ng/mL. For Hashimoto's thyroiditis, it was about 7.5 ng/mL. For unclassified autoimmune thyroid disease, it was about 2.2 ng/mL. These are average differences across 38 studies.
