Your thyroid gland keeps your body’s metabolism humming and plays a key role in your overall well-being. So if you have some type of thyroid disease, you’d know it, right?

Not necessarily, says endocrinologist Mary Vouyiouklis Kellis, MD. About 20 million Americans have one of these problems with the butterfly-shaped gland at the base of the neck:

• Hyperthyroidism (overactive thyroid)
• Hypothyroidism (underactive thyroid)
• Goiter (enlarged thyroid)
• Thyroid nodules
• Thyroid cancer

Here, Dr. Kellis shares the facts behind five myths you’ve heard about thyroid disease.

Myth No. 1: The symptoms of thyroid disease are obvious

The facts: The symptoms of thyroid disease can be subtle and easy to overlook.

Significant weight gain or loss, fatigue or irritability, and cold or hot sensitivity are quite common and could point to other health issues, too.

Because of symptom subtlety or overlap, thyroid disease can be tricky to diagnose, Dr. Kellis says.

A test for thyroid stimulating hormone (TSH) can identify thyroid problems before symptoms occur. But if you don’t report symptoms, your doctor may not screen you for thyroid disease.

Ask your doctor about screening if your family has a history of thyroid disease. Heredity is a factor in Graves’ disease, Hashimoto’s disease (a type of hypothyroidism) and thyroid cancer.

Myth No. 2: Hormone problems after 40 always mean menopause

The facts: It’s easy to chalk up hormonal symptoms — heavier or less frequent menstrual periods, mood fluctuations, sleep disturbances and heat sensitivity — to menopause.

Many women develop such problems as female hormones levels start to fluctuate in mid-life.

But changes in female hormones can sometimes affect thyroid function. And both menopause and thyroid disease are more common in women after age 40.

Don’t hesitate to mention any changes in your physical and mental well-being to your doctor. He or she can pinpoint their cause and help you find relief.

Myth No. 3: If you have thyroid disease, your eyes will bulge

The facts: Graves’ disease, the most common form of hyperthyroidism, sometimes — but not always — causes bulging eyes. (Smoking increases your risk of developing this problem.)

Other eye problems linked to Graves’ disease include double vision, dry eyes and swollen eyelids.

But just 10 to 20 percent of Graves’ disease patients develop significant eye disease, notes Dr. Kellis.

“We tell smokers with Graves’ disease to stop smoking,” she says. “We can treat eye disease with selenium supplements and steroids. And for severe bulging, we can do surgery.”

Myth No. 4: If you have a thyroid nodule, then you must have cancer

The facts: “Thyroid nodules are most often benign, and half the women over age 40 have them,” Dr. Kellis says.

So if a nodule develops on your thyroid gland, don’t hit the panic button. Doctors find cancer in fewer than 5 percent of thyroid nodules.

If the nodule is a solid 1 centimeter or larger, your doctor likely will take a sample of cells (biopsy) to see if it is cancerous.

“Many patients ask whether a blood test can determine if a nodule is cancerous,” she says. “However, the initial diagnosis of thyroid cancer is made by thyroid biopsy, not by a blood test.”

Myth No. 5: You’ll need iodine supplements for thyroid disease

The facts: You may hear that it’s important to take iodine supplements when you have thyroid disease.

Advertisers make this claim because iodine deficiency is the leading cause of thyroid disease around the world.

But in the United States, we get plenty of iodine from our diet (in salt, seafood, dairy products and eggs, for instance).

“I do not recommend iodine supplements,” says Dr. Kellis. “In fact, they can actually make your thyroid disease worse.”

The bottom line? Don’t believe everything you hear about thyroid disease and its treatment.

And if you’re concerned about symptoms, talk to your doctor to get the help you need, whether it’s for thyroid disease or a different problem.