Narcolepsy affects about 1 in 2,000 people in the United States. The condition causes symptoms including sleep disturbances, cataplexy (sudden loss of muscle tone), excessive daytime sleepiness, sleep paralysis, and hypnagogic hallucinations when falling asleep or waking up.

Narcolepsy’s symptoms involve more than sleep issues. The condition can cause:

• Depression
• Obesity
• Problems with concentration
• Poor memory

Some of the symptoms of narcolepsy overlap with those of hypothyroidism, a condition caused by an underactive thyroid gland. In addition to common symptoms, hypothyroidism and narcolepsy share other similarities.

What Is Hypothyroidism?

Hypothyroidism occurs when the thyroid gland fails to produce enough thyroid hormones. There are many causes of hypothyroidism, including damage to the thyroid, iodine deficiency, and lack of thyroid-stimulating hormone (TSH) from the pituitary gland in the brain. Surgery or radiation to treat an overactive thyroid (hyperthyroidism) or cancer, as well as inflammation from infection or autoimmune disease, can also lead to hypothyroidism.

Symptoms of hypothyroidism include some of the same symptoms seen in narcolepsy, including:

• Fatigue
• Weight gain
• Depression
• Memory problems
• Sleep disturbances

Other symptoms of hypothyroidism include:

• Poor cold tolerance
• Muscle weakness and soreness
• Constipation
• High cholesterol
• Heavy or irregular menstrual periods
• Dry skin
• Thinning hair
• Puffy face
• Hoarseness

Hypothyroidism in children and teens can cause physical and mental developmental delays. If left untreated, hypothyroidism can lead to many serious complications, such as heart problems, mental health issues, an enlarged thyroid gland, and myxedema (a life-threatening condition).

The main treatment for hypothyroidism is medication. Synthetic thyroid hormones replace the hormones normally produced by the thyroid.

Similarities Between Hypothyroidism and Narcolepsy

Hypothyroidism and narcolepsy share many similarities. Before modern thyroid function tests were developed, narcolepsy was regularly misdiagnosed as hypothyroidism.

Thyroid function tests are now used regularly to diagnose both hypothyroidism and hyperthyroidism. It is very easy to rule out thyroid problems in people with symptoms such as difficulty sleeping, tiredness, and depression.

However, the similarities between hypothyroidism and narcolepsy go beyond sharing symptoms. They can both be caused by autoimmune disease, they can both involve the hypothalamus, and they may both affect the metabolism of brown fat.

Autoimmune Disease

Both hypothyroidism and narcolepsy can be caused by autoimmune disease, which is when your immune system accidentally views your body as a threat and attacks it instead of protecting it. Type 1 narcolepsy is caused by the loss of neurons (brain cells) that secrete orexin (a messenger protein, also called hypocretin) in the hypothalamus. This is believed to be due to autoimmune disease.

Several types of hypothyroidism are caused by autoimmune disease, including Hashimoto’s thyroiditis. In addition, having one autoimmune condition is a risk factor for developing additional autoimmune diseases. Research has shown that type 1 narcolepsy is associated with a variety of autoimmune and allergic conditions, including thyroid dysfunction.

Hypothyroidism, Narcolepsy, and the Hypothalamus

Narcolepsy and thyroid function both involve the hypothalamus, a part of the brain involved in controlling metabolism, appetite, temperature regulation, and other important bodily functions. The hypothalamus controls these functions by affecting the secretion of thyroid hormones and orexin that is deficient in people with type 1 narcolepsy.

The hypothalamus secretes thyrotropin-releasing hormone, which causes the pituitary gland to secrete TSH. TSH causes the thyroid to make the thyroid hormones triiodothyronine (T3) and thyroxine (T4). Orexin, on the other hand, is produced by cells in the hypothalamus and exists throughout the brain and cerebrospinal fluid.

The connection between orexin and thyroid hormones is not fully understood, but there is evidence that the two are closely related. Research suggests that orexin may affect the release of thyrotropin-releasing hormone in the hypothalamus. Other research has shown that TSH levels are lower in people with type 1 narcolepsy.

Metabolism and Brown Fat

Both orexin and thyroid hormones influence metabolism and directly affect metabolic activity in brown adipose tissue (brown fat). Brown adipose fat is important for regulating body temperature and plays a role in regulating blood sugar and energy metabolism. Both narcolepsy and hypothyroidism may result in altered metabolism of the brown fat cells.

People with type 1 narcolepsy tend to have more body fat, even when they eat fewer calories. This is because they have a lower basal metabolism believed to be caused by less activation of brown fat cells by orexin. Similarly, thyroid hormones activate brown fat, which may help explain why people with hypothyroidism have a lower metabolism and cold intolerance.

Understanding Hypothyroidism and Narcolepsy

Aside from the similarities described above, hypothyroidism and narcolepsy are very different diseases with different treatments. However, they can both occur at the same time. Because of the similarities between the two diseases, it may be difficult to identify narcolepsy in people with hypothyroidism, especially if treatment for hypothyroidism improves some of the narcolepsy symptoms.

With current blood tests, it’s unlikely that narcolepsy could be mistaken for thyroid disease. However, health care providers may overlook narcolepsy in people with hypothyroidism. Hypothyroidism can often be diagnosed with a simple blood test, although narcolepsy takes an average of seven years from when symptoms begin to diagnosis. Several tests are used, including a multiple sleep latency test, polysomnography (sleep study), and a spinal tap.

“For most people, it takes years to get diagnosed because the symptoms of narcolepsy can be a lot of other things, too,” one MyNarcolepsyTeam member wrote. “I’m 57 years old and didn’t get diagnosed until 2006. I went to the doctor I don’t know how many times complaining of all the symptoms I had. They would check my thyroid and blood, and nothing ever was wrong there, so they chalked it up as depression and put me on antidepressants.”

Whether you are experiencing symptoms of narcolepsy, hypothyroidism, or any other medical condition, make sure you work with your health care provider to find the right diagnosis and treatments that work. Do not settle for “good enough” when it comes to your health.

Keep asking questions and searching for answers until you find relief from health issues that are affecting you. Most importantly, don’t lose hope. Never give up until you find the help that you need.

Talk With Others Who Understand

MyNarcolepsyTeam is the social network for people with narcolepsy. On MyNarcolepsyTeam, more than 8,000 members come together to ask questions, give advice, and share their stories with others who understand life with narcolepsy.

Are you or someone you care for living with narcolepsy and hypothyroidism? Share your experience in the comments below, or start a conversation by posting on your Activities page.