Do people with Hashimoto's thyroiditis have lower vitamin D levels?

People with Hashimoto's thyroiditis (HT), an autoimmune disease where the immune system attacks the thyroid gland, often want to know if their vitamin D is low and whether that matters. The short answer: many studies do find lower vitamin D in people with HT, and the gap seems largest in those whose thyroid has already become underactive. But the evidence is not unanimous, and researchers still cannot say whether low vitamin D helps cause HT or is a result of it.

What the research says

A large 2024 review pooled 38 observational studies and found that people with thyroid diseases had vitamin D levels about 5.42 ng/mL lower than people without thyroid disease ². A cross-sectional study of 776 patients found vitamin D insufficiency (defined as below 75 nmol/L) in 48.9% of people with HT, compared with 37.1% of people without autoimmune thyroid disease ¹¹. That same study found the lowest levels in people with overt hypothyroidism, meaning their thyroid was clearly underactive, at 60.4% insufficiency versus 44.1% in people with mild (subclinical) hypothyroidism ¹¹. A 2025 Korean study that measured vitamin D in blood and thyroid tissue also found significantly lower serum vitamin D in HT patients, and it found that the vitamin D receptor was actually more active in HT thyroid tissue, suggesting the body may be responding differently to vitamin D rather than simply having too little ⁹.

What to ask your doctor

• Should I have my vitamin D level checked, given my Hashimoto's diagnosis?
• My thyroid is underactive. Does good thyroid hormone control affect my vitamin D level?
• If my vitamin D is low, what are the options for correcting it, and how often should it be rechecked?
• Are there symptoms I should watch for that might point to low vitamin D?