Would you know if you had a thyroid problem? Say, you’re on a diet, but losing nary a pound. Or you’re experiencing an inexplicable weight gain. Maybe your skin and hair are dry, and you’re always tired. You’re constantly feeling cold or suffer from constipation and are having heavy periods. Many of these symptoms can easily be explained away by unhealthy eating, not exercising enough or being “run down.” But these also are some of the common symptoms of hypothyroidism, or underactive thyroid, in which too little hormone is produced.

The thyroid gland is located in the neck below the Adam’s apple. The hormone it secretes controls the body’s metabolism. As such, it affects your weight, mood, energy level, body temperature, condition of your skin and hair and just about every tissue in your body.

Thyroid diseases aren’t usually front and center when it comes to media health coverage. Yet, it’s the most common endocrine disorder in the United States. An estimated 27 million Americans have a thyroid condition, according to the American Association of Clinical Endocrinologists. Women account for most cases (80%), and about half of those suffering with a thyroid condition go undiagnosed because the symptoms vary and are commonly associated with other causes.

Hypothyroidism is the most common thyroid condition, involving about four out of five cases. It’s often present for several years before being diagnosed. Hypothyroidism is easily treated with thyroid hormone replacement.

The opposite condition, hyperthyroidism, involves an overactive thyroid, when too much hormone is produced. It’s characterized by nervousness, weight loss, rapid heartbeat, heat intolerance, insomnia, irregular and light periods, diarrhea, among other symptoms. Treatment usually involves taking radioactive iodine or antithyroid medicine.

In an interview on the VH1 show “Behind the Music” that aired June 29, rapper Missy Elliott said she has Graves Disease, a type of hyperthyroidism. The 39-year-old Grammy winner was diagnosed in 2008. She suffered from hair loss, mood swings and tremors; but after treatment her condition is now under control.

Other problems affecting the thyroid include nodules, goiters and cancer.

One in 12 to 15 young women have thyroid nodules. These are growths on the thyroid that appear as lumps. Most people do not know they have them, unless they are large enough to cause symptoms, such as problems swallowing. Nodules are overwhelmingly benign and usually do not need to be treated; only 5% are found to be cancerous. There is no known cause, but nodules tend to run in families. Also, a study published in 2007 found women with uterine fibroids have an increased incidence of thyroid nodules.

Some nodules develop into goiters. A goiter is an enlarged thyroid gland. It can be caused by a lack of iodine in the diet or if the thyroid is over or underactive. The condition is treated with thyroid hormone pills or, in some cases, surgery if the growth is pressing against other structures in the neck.

There is a growing trend in the number of thyroid cancers in the U.S. The National Cancer Institute estimates nearly 45,000 cases of thyroid cancer were diagnosed last year, 75% in women. Nearly two out of three cases are found in people between the ages of 20 and 55. Speculation is that radiation exposure from increased usage of CT scans of the head and neck, particularly in childhood, has increased the risk. A small number of people develop an inherited form of thyroid cancer. But the American Cancer Society notes that most people with thyroid cancer have no known risk factors. If you have a lump or swelling in your neck, hoarseness and persistent cough, see your doctor. The good news is that thyroid cancer is one of the least deadly cancers, with a 97% survival rate after five years.

If you suspect you are having symptoms related to the thyroid, ask your doctor about running a thyroid stimulating hormone (TSH) test.