Oprah Winfrey recently informed the nation on "Good Morning America" that she "blew out her thyroid" at the end of last season because of stress. But that isn't exactly a medical term. No one blows out a thyroid, says endocrinologist Dr. Terry Smith of Harbor-UCLA Medical Center. "What is that? Like a right rear tire on a Ferrari?" he asks.
Winfrey then wrote about her medical condition in the October issue of her magazine, O, elaborating that she had both kinds of thyroid disease -- an overactive thyroid and then an underactive one, both considered autoimmune diseases.
The American Assn. of Clinical Endocrinologists estimates that about 27 million Americans have one of these problems, more than half of whom don't realize it. Possibly because of reproductive hormones or other still unknown reasons, women get autoimmune diseases more often then men, and about four times more women than men get thyroid disease.
Stress affects the immune system, but can stress spark an autoimmune disease that damages or impairs the thyroid gland?
The thyroid is a small gland at the base of the neck above the collarbone (it's what swells in people with goiters). The gland pumps out two main thyroid hormones, called T3 and T4, which regulate metabolism. "Every single tissue needs thyroid hormone," says endocrinologist Dr. Peter Singer of USC's Keck School of Medicine.
Thyroid disease begins when the body starts to make antibodies to attack the gland's healthy tissue. Researchers have a variety of theories about why this happens. One theory is that when the immune system fights off bacteria from an infection, it inadvertently harms the thyroid as well.
The type of thyroid disease that develops depends on the kinds of antibodies made, and inherited genes partly determine that.
Some people begin to make antibodies that stimulate the gland to overproduce thyroid hormones. Pregnancy or stress, such as what a celebrity might experience, can in fact instigate this.
"Potent physical or emotional stress can cause an overactive thyroid in those people who have the underlying genetic background," says Singer.
Too much thyroid hormone speeds up metabolism. People lose weight, their heart beats rapidly, they have palpitations. "It feels like you're amped up," says Singer. "You've got all the symptoms of being in love." Although the thyroid gland might slow down on its own, doctors usually treat the condition before that happens.
An obvious symptom of an overactive thyroid is a bulging of the eyes because the tissue behind them have become inflamed, pushing on the back of the eyeballs. "There are about 100,000 people or so who walk around with bulging eyes," says Smith. Some experience double vision and, in serious but rare cases, people can go blind. Smith and colleagues are developing a therapy that blocks the inflammation in that tissue.
People with overactive thyroids are treated with medications or radioactive iodine that kills off part of the thyroid, or surgery that snips out part or all of the gland. After any of these regimens, overactive-thyroid patients usually have to go on the same drugs that underactive-thyroid patients take.
Underactive thyroid is far more common than the overactive kind and occurs when the autoimmune antibodies destroy thyroid tissue. It hits middle-aged men and women. "At Oprah's age,  about 6 to 7% of women have it," says Singer. People who have low thyroid levels feel sluggish, as if they're not running on all cylinders. Also, they gain weight. "They gain no more than about 10% of their baseline weight," says Singer. "As their metabolism slows, so does their appetite."
They can also have dry skin and hair, depression and other symptoms. Patients are treated with medications that replace the lost hormones.
To check for thyroid disease, doctors do a simple blood test that measures the amount of T3 and T4 as well as thyroid-stimulating hormone, which prods the thyroid into making T3 and T4 in the first place.
The ratio of the three hormones to each other reveals whether the thyroid is over- or underactive. Sometimes physicians will first test for T4, the main hormone, then test again if it is abnormal.
The American Thyroid Assn. recommends that everyone over 35 get tested for thyroid function because the diseases so often go undiagnosed. Winfrey was long overdue.