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However, some research suggests that an underactive thyroid may contribute to the progression of certain types of bipolar disorder, especially if someone has susceptible to the condition. Thyroid function can also influence the severity of symptoms.
Changes in the hypothalamic-pituitary-thyroxine (HPT) axis are common in bipolar disorder. The HPT axis regulates many body functionsincluding hormone and neurotransmitter levels associated with mood and thyroid function.
Research into this connection is so far inconclusive, but a 2021 study Suggested thyroid hormone levels in people with bipolar disorder may change mood episodes. The study participants experience manic episodes (periods of elevated mood) seemed to have higher levels of thyroid hormones than those who suffered from them depressive episodes.
Only one small study from 2019 contradicts these findings. The study found no evidence of significant changes in thyroid hormone levels between mood episodes in bipolar disorder.
A 2023 studywhich examined early episodes of bipolar disorder in women, revealed clinical signs of thyroid dysfunction in 27% of participants who experienced a manic or hypomanic episode and 60% who experienced depressive episodes.
In concrete terms, researchers discovered this triiodothyronine (T3) hormone testing showed lower hormone levels in people experiencing a first episode of bipolar depression than in those experiencing mania or hypomania for the first time. Lower T3 levels have also been linked to more severe symptoms.
Researchers concluded that the findings may show that thyroid dysfunction disrupts mood and affects the progression of bipolar disorder in people already predisposed to the condition.
More research with different populations and larger sample sizes is needed to further understand the underlying mechanisms of this relationship.
The link between lithium and hypothyroidism
Although the exact mechanism is not clear, experts believe that lithium inhibits the release of thyroid hormones T3 T4 (thyroxine).
A other research from 2023 found that 32% of participants receiving long-term lithium treatment for bipolar disorder developed thyroid disease during treatment. Of those, 79% were diagnosed with hypothyroidism.
Ultimately, the relationship between hypothyroidism and bipolar disorder is complex and misunderstood. This concerns factors such as the role of thyroid hormones on mood, the… type of bipolar disorderthe underlying causes of hypothyroidism and the type of treatment.