Millions of Americans -- mostly women -- could find the key to more energy, easier weight control, sharper thinking, less depression, less infertility, lower blood pressure and lower incidence of heart disease. It all depends on who wins a 10-year-old medical debate.
The holdup is the number on a lab test -- specifically, the reference range for thyroid-stimulating hormone.
Many physicians who specialize in endocrine disorders, including thyroid disease, think lab limits for thyroid-stimulating hormone are too broad, leaving many patients who suffer from low-thyroid disease undiagnosed and untreated.
A butterfly-shaped gland that sits at the base of the throat, the thyroid governs metabolism. When it doesn't make enough thyroid hormone, people feel sluggish, have trouble concentrating, gain weight and feel cold. Left untreated, thyroid disease can lead to more-serious health problems.
Conversely, an overactive thyroid causes people to feel anxious, jittery and hot, and can cause rapid heartbeat and insomnia.
Overseeing all this is the brain's pituitary gland. When it senses that the thyroid isn't producing enough thyroid hormone, it sends out thyroid-stimulating hormone, also called thyrotropin, to tell the thyroid gland to step up production.
Thus, a high thyrotropin means the thyroid is underactive, causing hypothyroidism. A low level indicates that thyroid levels are too high, creating hyperthyroidism.
Low thyroid is 20 times more common, and among those it affects, 80 percent are women.
Most hypothyroidism occurs when the body makes antibodies that attack the thyroid gland. Treatment is simple and involves taking a daily bioidentical thyroid pill.
Dr. Mark Lupo, a Sarasota, Fla., endocrinologist who specializes in thyroid disorders, estimates that 25 million Americans, or about 12 percent of adults, currently have a low-thyroid condition, and only half are detected. Many endocrinologists think the labs' upper ranges of 4.2 to 5.5 are too high and should be 3. Opponents think lowering the limit would lead to increased costs and overtreatment.
"In the medical community, the issue is not seen as very serious," said Dr. Leonard Wartofsky, an endocrinologist who thinks anything over 2.5 should be looked at.
"No one will die from a thyroid-stimulating hormone that's 4.5," he said. "So what if you're a little tired, a little fat, a little blue; doctors think, 'I have people with cancer.'"