An estimated 20 million Americans have some form of thyroid disease, and up to 60 percent of them don’t know it. That means roughly 12 million people in the U.S. alone are walking around with an undiagnosed thyroid condition, often attributing their symptoms to stress, aging, or poor sleep.
The Numbers in the U.S.
Thyroid problems fall into a few major categories, and their prevalence adds up quickly. About 5 in 100 Americans ages 12 and older have hypothyroidism, where the thyroid doesn’t produce enough hormone. Most of these cases are mild or cause few obvious symptoms, which helps explain why so many go undetected. The most common cause of hypothyroidism in the U.S. is Hashimoto’s disease, an autoimmune condition where the immune system gradually attacks thyroid tissue.
Hyperthyroidism, the opposite problem where the thyroid produces too much hormone, affects about 1 percent of the population. Women are diagnosed far more often than men. Thyroid cancer, while less common, still accounts for an estimated 45,240 new diagnoses in 2026 alone, at a rate of about 13.7 cases per 100,000 people per year.
Why Women Are Affected Far More Often
Women are three to four times more likely than men to be diagnosed with thyroid cancer, and the gap is even wider for other thyroid conditions like Hashimoto’s and Graves’ disease. The reasons aren’t entirely settled. Some researchers point to estrogen’s potential effect on thyroid cell growth, though studies conflict on whether hormones actually drive thyroid disease or simply correlate with it.
A more practical explanation is that women tend to seek medical care more frequently, which means small, symptom-free thyroid abnormalities get caught on imaging that might never have been ordered for a man with the same condition. Improvements in ultrasound technology have increased detection of tiny thyroid tumors (under 1 centimeter), especially in women. For aggressive or advanced thyroid cancers, the gender gap largely disappears, with incidence roughly equal between men and women.
Risk Rises Sharply With Age
Thyroid problems become significantly more common after 60. A large study of adults 65 and older in the Atherosclerosis Risk in Communities cohort found that nearly 25 percent had some form of thyroid dysfunction. That includes people already on medication (17 percent of participants) and those with undetected problems. Among untreated older adults in the study, about 6 percent had mildly underactive thyroids and nearly 1 percent had more significant hypothyroidism.
This matters because thyroid symptoms in older adults, things like fatigue, weight changes, memory trouble, and feeling cold, overlap heavily with what people assume is just normal aging. A simple blood test can distinguish between the two, but many older adults never get one unless they specifically ask or a doctor suspects something.
Why So Many Cases Go Undiagnosed
The 60 percent undiagnosed figure from the American Thyroid Association reflects how easy thyroid disease is to miss. Mild hypothyroidism often develops gradually over years. You might gain a few pounds, feel more tired than usual, notice your skin getting drier, or find it harder to concentrate. None of these symptoms on their own scream “thyroid problem,” and most people chalk them up to something else entirely.
Hyperthyroidism can be equally deceptive. A racing heart, anxiety, weight loss, and trouble sleeping could point to dozens of conditions or simply a stressful period in your life. The overlap with common complaints is precisely why thyroid disease hides in plain sight for so long.
How “normal” thyroid function is defined also plays a role. The standard reference range for thyroid blood tests is based on results from the middle 95 percent of healthy adults with no thyroid problems. The 2.5 percent above and below that range are flagged as abnormal. This means people sitting just inside the normal boundary might still have symptoms, but their lab results won’t trigger a diagnosis.
The Most Common Thyroid Conditions
- Hashimoto’s disease: The leading cause of hypothyroidism in the U.S. The immune system slowly damages the thyroid, reducing its hormone output over months or years. Many people have it for a long time before levels drop enough to cause noticeable symptoms or show up on blood work.
- Graves’ disease: An autoimmune condition that pushes the thyroid into overdrive, causing hyperthyroidism. Symptoms include unexplained weight loss, heat intolerance, trembling hands, and eye irritation or bulging.
- Thyroid nodules: Small lumps that form in the thyroid gland. Most are harmless and never cause symptoms. A small percentage turn out to be cancerous, which is why doctors sometimes recommend a biopsy if a nodule is large or has suspicious features on ultrasound.
- Thyroid cancer: Highly treatable in most cases, with a five-year survival rate well above 95 percent for the most common type (papillary thyroid cancer). About 45,000 new cases are expected annually in the U.S.
The Financial Weight of Thyroid Disease
Beyond the physical toll, thyroid disease carries a real economic cost. Data from the Agency for Healthcare Research and Quality found that $4.3 billion was spent on thyroid disease treatment among adult women alone in a single year. More than half of that went to office and outpatient visits ($2.2 billion), with another $1.4 billion spent on prescription medications. The average per-person cost for women being treated was $343 per year, though that figure doesn’t capture the indirect costs of missed work, reduced productivity, or the months and sometimes years of feeling unwell before getting a diagnosis.
For a condition that’s straightforward to detect with a blood test and manageable with daily medication in most cases, the real cost of thyroid disease may be the sheer number of people living with it unnecessarily, unaware that a simple screening could change how they feel every day.