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En español | You may have never given your thyroid a moment’s thought until something like a racing heart, fatigue or mysterious weight gain sent you scuttling to your doctor’s office in search of a fix. Could this much-discussed but little-understood gland at the front of your neck be to blame?

Yes. In fact, your tiny thyroid gland (which normally weighs less than an ounce) plays a significant role in everything from your heart rate to your toenails. It’s been called your body’s control center because the hormones it produces keep your brain, heart rate, breathing, nervous system, weight, body temperature, cholesterol, metabolism and more operating at top efficiency.

How it works: The thyroid is signaled by the pituitary and the brain’s hypothalamus to turn iodine from the food you eat into the hormones triiodothyronine (T3) and thyroxine (T4), which are then sent through your bloodstream to feed your body’s cells. In a feedback loop, the pituitary monitors the hormone levels in your blood and signals the thyroid to either produce more or less of them.

What can go wrong?

For more than 5 percent of adults — and far more women than men — the T3 and T4 balance gets out of whack. Experts say that about 1 in 8 women will experience a thyroid problem in her lifetime.

Continued overproduction of these hormones by the thyroid, or hyperthyroidism (including Graves’ disease), is most common in women of reproductive age and can cause the following:

  • rapid heart rate
  • anxiety
  • irritability or moodiness
  • nervousness or hyperactivity
  • sweating or sensitivity to high temperatures
  • trembling or tremors
  • hair loss
  • unexpected weight loss
  • difficulty sleeping
  • diarrhea
  • muscle weakness
  • increased thirst

If your thyroid is not able to produce enough T3 and T4, or is underactive, you have hypothyroidism. You may also suffer from an autoimmune disease called Hashimoto, which is the most common cause of hypothyroidism. Peter Singer, M.D., professor of clinical medicine at the Keck School of Medicine, University of Southern California, notes that 80 percent of such cases are in women. And rates increase with age: 3 percent of women in their 40s, about 10 percent of women 65 years old and 20 to 25 percent of women 75 or older have this problem.

The symptoms of hypothyroidism can be any of the following:

  • trouble sleeping
  • fatigue and lack of energy
  • inappropriate weight gain or inability to lose weight
  • difficulty concentrating, brain fog or memory loss
  • dry skin and hair, and brittle nails
  • hair loss
  • depression
  • constipation
  • sensitivity to cold temperatures
  • joint and muscle aches
  • decreased libido

Rarer problems of the thyroid include abnormal growth of the gland, such as goiters, which can compress the windpipe; nodules (50 percent of people will develop them as they age; they are benign in most cases); and thyroiditis, which results from inflammation within the gland. Cancer in the thyroid can develop, too, and is both treatable and survivable, especially if caught early.

Testing your hormone levels

To determine if you have an issue with your thyroid, a doctor will order a simple blood test measuring TSH, which should fall between .4 and 4.0 milli-international units per liter (mIU/L).

James Hennessey, M.D., director of clinical endocrinology at Beth Israel Deaconess Medical Center, notes that studies indicate that higher levels of TSH can be normal as we age.