A thyroid disorder is any condition that prevents your thyroid gland from making the right amount of hormones your body needs. About 20 million Americans live with some form of thyroid disease, and the conditions range from a mildly underactive gland that’s easily managed with medication to thyroid cancer. Most thyroid disorders are lifelong but highly treatable once identified.
What Your Thyroid Does
Your thyroid is a small, butterfly-shaped gland in the front of your neck, wrapped around your windpipe. Its primary job is controlling your metabolic rate, the process your body uses to convert food into energy. It does this by releasing two hormones into your bloodstream. The first, T4, is the hormone your thyroid produces in the largest quantity, but it doesn’t directly affect metabolism very much. Instead, your body converts T4 into the second hormone, T3, which has a much stronger effect on how fast your cells burn energy.
Because these hormones influence nearly every organ system, even a small imbalance can produce symptoms that show up across your entire body. Too little hormone and everything slows down. Too much and everything speeds up.
Hypothyroidism: An Underactive Thyroid
Hypothyroidism means your thyroid isn’t producing enough hormone to keep your metabolism running at its normal pace. The most common cause is Hashimoto’s disease, an autoimmune condition in which your immune system gradually damages the thyroid. Other causes include inflammation of the gland, surgical removal of part or all of the thyroid, radiation treatment, certain medications, and, rarely, problems with the pituitary gland or too little iodine in the diet. Some people are born with an underactive thyroid.
Symptoms tend to develop slowly and can be easy to dismiss as normal aging or stress. They include:
- Fatigue and sluggishness
- Unexplained weight gain
- Trouble tolerating cold
- Dry skin and thinning hair
- Constipation
- Joint and muscle pain
- A puffy face
- Heavy or irregular menstrual periods
- Depression
- A slowed heart rate
Treatment typically involves taking a daily synthetic thyroid hormone pill that replaces what the gland can no longer produce on its own. Most people who start this medication take it for the rest of their lives, with periodic blood tests to make sure the dose stays accurate.
Hyperthyroidism: An Overactive Thyroid
Hyperthyroidism is the opposite problem: the thyroid floods the body with too much hormone, pushing metabolism into overdrive. The most common cause is Graves’ disease, another autoimmune condition, but this time the immune system stimulates the thyroid to overproduce. Overactive thyroid nodules, thyroid inflammation, excess iodine from supplements or medications, and taking too high a dose of thyroid hormone medication can also trigger it.
Where hypothyroidism makes everything feel slow, hyperthyroidism makes everything feel revved up:
- Nervousness, irritability, or mood swings
- Rapid or irregular heartbeat
- Trouble tolerating heat
- Unexplained weight loss
- Tremor, often in the hands
- Muscle weakness
- Frequent bowel movements or diarrhea
- Trouble sleeping
- Fatigue
Notice that fatigue appears on both lists. That’s part of what makes thyroid disorders tricky to recognize from symptoms alone. The body doesn’t function well when hormones are out of range in either direction.
Hyperthyroidism can be treated with medications that suppress hormone production, or with radioactive iodine therapy, which works by killing overactive thyroid cells and shrinking the gland. One important thing to know about radioactive iodine: it’s difficult to calibrate precisely, so many people who undergo the treatment end up with an underactive thyroid afterward and need to take hormone replacement pills long-term.
Thyroid Nodules and Goiter
A goiter is an irregular enlargement of the thyroid gland that can make the front of your neck look swollen. It sometimes causes difficulty swallowing or breathing. A goiter can develop in both hypothyroidism and hyperthyroidism, and it can also appear when the thyroid is functioning normally.
Thyroid nodules are lumps that form when thyroid cells grow abnormally. They’re extremely common, especially as people age, and the vast majority are benign. About 5% of thyroid nodules are found to contain cancer. Most nodules produce no symptoms and are discovered incidentally during an imaging scan or physical exam. Some nodules become overactive and start producing excess thyroid hormone on their own, which can lead to hyperthyroidism.
Thyroid Cancer
Thyroid cancer is one of the most treatable cancers. The overall five-year survival rate is 98.3%, according to National Cancer Institute data. When the cancer is still confined to the thyroid, the five-year survival rate is 99.9%. Even when it has spread to nearby lymph nodes, survival remains high at 98.1%. The picture changes significantly if the cancer metastasizes to distant parts of the body, where the five-year survival rate drops to about 48%, but distant spread is uncommon at the time of diagnosis.
Treatment usually involves surgical removal of the thyroid, often followed by radioactive iodine therapy to destroy any remaining cancer cells. After surgery, patients take thyroid hormone replacement for life.
How Thyroid Disorders Are Diagnosed
Diagnosis starts with a blood test measuring TSH, the signal your pituitary gland sends to tell the thyroid how much hormone to make. When the thyroid is underactive, TSH rises because the pituitary is working harder to compensate. When the thyroid is overactive, TSH drops because the pituitary is trying to slow things down. A second measurement, called free T4, confirms how much hormone the thyroid is actually releasing. Values in the top and bottom 2.5% of the normal range are considered abnormal.
If nodules or structural changes are suspected, an ultrasound of the neck gives a detailed picture of the gland. Nodules that look concerning may be biopsied with a thin needle to check for cancer cells.
Who Is Most at Risk
Women are five to eight times more likely than men to develop a thyroid condition. The reasons aren’t fully understood, but hormonal and immune system differences likely play a role, since the two most common thyroid disorders, Hashimoto’s and Graves’ disease, are both autoimmune. Risk also increases with age, a family history of thyroid or autoimmune disease, and a personal history of other autoimmune conditions.
Because symptoms like fatigue, weight changes, and mood shifts overlap with so many other conditions, thyroid disorders often go unrecognized. A simple blood test can confirm or rule out a thyroid problem, and it’s worth requesting one if you have persistent symptoms that don’t have another clear explanation, particularly if you fall into a higher-risk group.