Is vitamin D lower in Graves' disease compared to healthy people?

People with Graves' disease, an autoimmune condition that causes an overactive thyroid, do tend to have lower blood levels of vitamin D than healthy people of similar age and sex. The finding shows up across several studies, but the size of the gap is modest and the evidence has some limits. Vitamin D is a hormone-like nutrient measured in the blood as 25-hydroxyvitamin D (often written 25(OH)D).

What the research says

A large review that pooled 38 observational studies found that people with thyroid diseases had vitamin D levels about 5.42 ng/mL lower than people without thyroid disease ¹. A smaller cross-sectional study of 84 patients with newly diagnosed Graves' disease and 42 healthy controls found average vitamin D levels of 19.2 ng/mL in the Graves' group versus 23.8 ng/mL in controls, a statistically significant difference ⁹. A separate case-control study also reported that vitamin D was significantly lower in Graves' disease than in healthy controls, with 70% of Graves' patients deficient compared with 20% of healthy controls ¹⁰.

What to ask your doctor

• Should my vitamin D level be checked given my Graves' disease? What level counts as low for someone with my condition? Could low vitamin D affect my thyroid treatment or my bone health? Are there other reasons my vitamin D might be low, such as diet, sun exposure, or other medicines? Do I need follow-up testing if my level is low?