Is Hashimoto’s thyroiditis associated with lower vitamin D and iron status?

Hashimoto’s thyroiditis has been linked to lower measured vitamin D and iron status, especially in observational studies of women, but the findings do not establish that thyroid autoimmunity itself consumes or directly depletes either nutrient.

Clinical evidence

• A meta-analysis of 25 observational studies (2,695 Hashimoto’s cases; 2,263 controls) found lower serum 25-hydroxyvitamin D in affected participants (Cohen’s d −0.62, 95% CI −0.89 to −0.34) and greater odds of vitamin-D deficiency (OR 3.21, 95% CI 1.94–5.30).
• Iron findings are concentrated in reproductive-age women. One cohort reported mean ferritin of 24.7 µg/L in women with Hashimoto’s versus 39.3 µg/L in controls; other studies also found lower ferritin, serum iron, or more frequent iron deficiency.

Mechanisms and alternative explanations

• Vitamin-D associations may reflect adiposity, season, latitude, sun exposure, lifestyle, supplementation, comorbidity, and assay methods. A longitudinal cohort found no lower baseline vitamin D among those who later developed anti-TPO antibodies, including at seroconversion; adjusted cross-sectional data likewise found no significant difference after accounting for age, sex, BMI, smoking, and season.
• Low iron may result from menstrual or gastrointestinal blood loss, thyroid dysfunction, or altered inflammatory iron handling rather than thyroid antibodies directly. Hashimoto’s can co-occur with autoimmune gastritis and celiac disease: reduced gastric acid in autoimmune gastritis and duodenal injury in celiac disease can impair iron absorption. Ferritin also rises with inflammation, complicating its interpretation.

Clinical implications

• For a 32-year-old woman with Hashimoto’s, testing vitamin D or iron status can be clinically reasonable when symptoms, dietary risk, heavy menstrual bleeding, or gastrointestinal features support it; abnormal results warrant evaluation for their specific cause rather than attribution to autoimmunity alone.

Bottom line

• Hashimoto’s is associated with lower vitamin D and iron indices in some populations, but current evidence does not show that thyroid autoimmunity directly depletes these nutrients or that supplementation treats the autoimmune disease itself.