Can thyroid conditions cause depression?

What does the thyroid do?

The thyroid is a gland located in the front of the neck, around the windpipe, that influences the body's metabolism, development, and growth.

The thyroid gland releases hormones called triiodothyronine, also referred to as T3, and thyroxine, also referred to as T4. T3 and T4 help regulate several bodily functions, including digestion, weight, heart rate, breathing, and mood.

Conditions that affect the thyroid can cause the release of too much or too little of these hormones, which results in several different physical and psychological symptoms ^[1][2].

Signs and symptoms of thyroid conditions

Different types of thyroid conditions include ^[1][2]:

• Hyperthyroidism: Overactive thyroid
• Hypothyroidism: Underactive thyroid
• Goiter: Enlarged thyroid
• Nodules: Benign lumps in the thyroid
• Thyroiditis: Swelling of the thyroid
• Thyroid cancer: Malignant lumps in the thyroid

These conditions can cause a range of symptoms, and symptoms may vary from person to person. The most common thyroid conditions are hyperthyroidism and hypothyroidism.

Common symptoms of hyperthyroidism include ^[3][4]:

• Fatigue
• Weight loss
• Heat sensitivity
• Shaking
• Restlessness
• Swelling of the face or neck
• Increased heart rate
• Mood swings
• Irritability
• Anxiety
• Depression
• Insomnia
• Loss of libido
• Increased thirst
• Diarrhea

Common symptoms of hypothyroidism include ^[5][6]:

• Fatigue
• Dry skin and hair
• Slowed movements
• Menstrual abnormalities and irregularities
• Fertility and pregnancy issues
• Weight gain
• Pain in the joints and muscles
• Decreased heart rate
• Sensitivity to the cold
• Swelling in the face or neck
• Depression
• Constipation
• Loss of libido

What is hypothyroidism?

Hypothyroidism, also referred to as underactive thyroid, is a condition that causes the thyroid to release a significantly reduced level of hormones. A decrease in thyroid hormones can cause reduced functioning in several organs and areas of the body. In hypothyroidism bodily functions become significantly reduced or slowed, and, in rare case, the condition can become life-threatening ^[2].

Hypothyroidism can occur as a result of several different causes, including inflammation, autoimmune disorders, surgery, and some medications. Symptoms often emerge slowly, so they might not be immediately noticeable. Also, they can be similar to symptoms of other conditions, which may result in misdiagnosis ^[6].

Can thyroid conditions cause depression?

There have been discussions and research on the link between thyroid function and psychiatric disorders for decades. It is believed that there is a clear link between thyroid conditions and depression. There is a more considerable prevalence of clinical depression amongst those with hyperthyroidism and hypothyroidism than in the general population ^[7][8].

However, the cause of this link remains unclear. Many studies have aimed to determine whether thyroid conditions cause depression or are simply comorbidities, which is yet to be established. The effect of hypothyroidism on the prevalence of depression has been extensively researched, while research into the link between hyperthyroidism and depression is limited ^[9][10].

The regulation and release of thyroid hormones are influenced by the hypothalamus-pituitary-thyroid (HPT) axis. The hypothalamus releases thyrotropin-releasing hormone (TRH), which causes the pituitary gland to release thyroid-stimulating hormone (TSH). In turn, this causes the thyroid to release hormones T3 and T4 ^[2][8].

Abnormalities in the levels and functioning of TRH and TSH have been found in depressed patients, thus suggesting a significant association between depression and thyroid function ^[7][8].

Hypothyroidism

Several studies have found higher rates of depression in patients with hypothyroidism and subclinical hypothyroidism than those without a thyroid condition. These studies have found a clear association between hypothyroidism and changes or abnormalities in mood, cognition, and mobility ^[8][11].

Furthermore, individuals with depression and hypothyroidism are more likely to have treatment-resistant depression, psychotic symptoms, and more severe symptoms than individuals with depression alone ^[7].

Low serotonin levels, which can contribute to depression, can influence the HPT axis. TSH release may be suppressed by low serotonin levels, thus leading to a reduction in thyroid hormone secretion. As such, both depression and hypothyroidism may be caused by reduced serotonin levels ^[7][12].

Similarly, research shows that hypothyroidism can significantly increase the risk of suicidal ideation and attempts in depressed individuals, particularly women ^[7][8].

Hyperthyroidism

The relationship between hyperthyroidism and depression is unclear. However, there is evidence of a higher prevalence of depression in individuals with hyperthyroidism than in those without a thyroid condition ^[9][13].

Hypothyroidism is mainly associated with depression, although, it has been found to contribute to symptoms of several mental health conditions, including signs of depression, anxiety, mania, psychosis, and emotional lability.

Hyperthyroidism causes increased adrenergic activity, leading to many symptoms of anxiety, such as increased heart rate, restlessness, and difficulty sleeping ^[10][13]. Anxiety is more common in people with hyperthyroidism, occurring in around two-thirds of those with the condition, while depression occurs in over one-third ^[8].

Similarly, many symptoms of both hyperthyroidism and hypothyroidism overlap with symptoms of depression. This includes excessive fatigue, weight changes, mood swings, irritability, stomach and muscle pains, and loss of libido. As such, it is considered possible to reduce depressive symptoms by treating the thyroid condition ^[8][9][14].

Treatment for thyroid conditions and depression

As evidence suggests a strong link between thyroid abnormalities and depression, it is recommended that individuals with depression should be tested for their thyroid hormone levels. Testing for thyroid hormone levels will involve a blood test to ascertain TSH, T3, and T4 levels. It may also be necessary to receive tests for inflammation and scans to check for nodules ^[4][6].

Often, medication to treat abnormalities in thyroid functioning can help to reduce symptoms of depression. As the levels of thyroid hormones are either reduced (hypothyroidism) or increased (hyperthyroidism), medications or other treatments can be prescribed to help these levels return to normal ^[2].

Hypothyroidism

To increase thyroid hormone levels, individuals can be prescribed levothyroxine. This can be prescribed alone or as an additional medication alongside an antidepressant. Some research suggests that combining levothyroxine and an antidepressant can significantly improve the treatment and recovery of hypothyroidism and depression ^[7][8].

Hyperthyroidism

individuals can be prescribed antithyroid medication, also known as thionamides, to reduce thyroid hormone levels. These medications can help to control thyroid hormone levels, although it may be necessary to continue taking the medication for several months before noticing an effect.

For some, this treatment can be stopped when levels are controlled, while for others, it may be necessary to continue taking the medication long-term. Initially, some unpleasant side effects can occur, which will reduce as the body adjusts to the medication ^[3][4].

Hyperthyroidism can also be treated by radioactive iodine treatment or surgery.

Radioactive iodine treatment involves swallowing a substance containing iodine and a low radiation dose. This reduces hormonal production in the thyroid by destroying cells. Although it can take weeks or months for the treatment to take effect, it may only be necessary to have one treatment to cure the condition ^[4].

Surgery can be performed to remove part or all of the thyroid, thus preventing symptoms of hyperthyroidism and reducing swelling. After surgery, it is usually necessary to take levothyroxine as the body no longer produces any thyroid hormones ^[3].

Antidepressants

While it may be possible to reduce depression symptoms by treating the thyroid condition alone, it is sometimes also necessary to take antidepressant medication. Some research suggests that certain antidepressants can impact thyroid hormone levels, so careful monitoring may be required during this treatment ^[8].

Other treatments

Symptoms of depression can also be treated and managed with the use of therapy and self-care. Therapy can help individuals manage emotional distress and develop positive coping strategies. Self-care techniques, such as eating a healthy diet, getting plenty of sleep, engaging in regular exercise, and utilizing relaxation exercises, can also improve symptoms ^[13][14].