Relationship Between Mood Disorders and Thyroid Changes

The thyroid gland, located at the base of the neck, produces hormones that regulate the body's metabolism, growth and development. Changes in the levels of these hormones, such as hypothyroidism (low production) and hyperthyroidism (high production), can have a significant impact on mental health, influencing the development of mood disorders. Studies demonstrate a strong association between thyroid dysfunction and disorders such as depression and bipolar disorder. In hypothyroidism, depressive symptoms may include fatigue, mental sluggishness, anhedonia, and weight gain. In hyperthyroidism, anxiety, insomnia and irritability are more frequent. The bidirectional relationship between thyroid and mood is complex and involves several mechanisms. Changes in thyroid hormone levels can affect brain neurotransmission, especially serotonin and dopamine, neurotransmitters directly related to mood. Furthermore, the hypothalamic-pituitary-thyroid axis, responsible for thyroid hormonal regulation, can also be influenced by psychological factors such as stress. Objective: To carry out a systematic review of the literature to evaluate the relationship between mood disorders and thyroid changes, investigating the prevalence of mood disorders in individuals with thyroid diseases, the underlying pathophysiological mechanisms and the impact of hormone replacement on mental health. Methodology: The review followed the PRISMA checklist guidelines. The PubMed, Scielo and Web of Science databases were searched using the following descriptors: "mood disorders", "hypothyroidism", "hyperthyroidism", "thyroid" and "mental health". Articles published in the last 10 years were selected. Inclusion criteria: studies that evaluate the relationship between mood disorders and thyroid diseases; Human studies; Published in Portuguese, English or Spanish; Published in the last 10 years. Exclusion: Animal studies; Studies with inadequate methodological designs; Studies that do not evaluate the relationship between mood and thyroid. Results: 15 studies were selected. The review identified that the prevalence of mood disorders is significantly higher in individuals with thyroid disease than in the general population. Hypothyroidism is associated with depression, while hyperthyroidism is more related to anxiety. The pathophysiological mechanisms underlying the relationship between mood and thyroid are complex and involve changes in cerebral neurotransmission, the hypothalamic-pituitary-thyroid axis and the response to stress. Adequate hormone replacement for thyroid disease can significantly improve symptoms of mood disorders in many cases. Conclusions: The systematic review confirmed the strong association between mood disorders and thyroid changes. Thyroid dysfunction can be a risk factor for the development of mood disorders, and adequate hormone replacement can be an important therapeutic tool.