TG and selenium deficiency: 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