Finally, selenium is essential for the maintenance of thyroid health and thyroid hormone metabolism.71–73 The thyroid gland plays a critical role in mental health,89 and thyroid hormones are among the therapeutic augmentation options in treatment-resistant depression.90 Consistently, the effects of selenium deficiency on mood could be partly mediated by selenium deficiency-induced changes in thyroid function.71 The modulation of thyroid function may be particularly relevant in patients with PCOS,91 explaining the benefits found in this group of patients.53 Here, TG is linked to major depressive disorder.