Problems with estrogen and testosterone, the body's main sex hormones, tend to attract widespread public interest. But we might all be better off paying more attention to a far more common endocrine disorder: abnormal levels of thyroid hormone. Thyroid disorders can affect a wide range of bodily functions and cause an array of confusing and often misdiagnosed symptoms.

Because the thyroid, a small gland in the neck behind the larynx, regulates energy production and metabolism throughout the body, including the heart, brain, skin, bowels and body temperature, too much or too little of its hormones can have a major impact on health and well-being.

Yet in a significant number of people with thyroid deficiencies, routine blood tests fail to detect insufficient thyroid hormone, leaving patients without an accurate explanation for their symptoms. These can include excessive fatigue, depression, hair loss, unexplained weight gain, constipation, sleep problems, mental fogginess and anxiety. Women of childbearing age may have difficulty getting pregnant or staying pregnant.

Although thyroid disorders are more common in adults, children, whose cognitive and physical development depend on normal thyroid function, are not necessarily spared. In a review article published last year in JAMA Pediatrics, doctors from the Children's Hospital of Philadelphia pressed primary care doctors to recognize childhood thyroid disease and begin treatment as early as the second week of life.

Symptoms of thyroid dysfunction vary widely from person to person and tend to develop gradually, so patients and doctors may not recognize them as a problem warranting exploration and treatment.

Hypothyroidism — low hormone levels — in particular is often misdiagnosed, its symptoms resembling those of other diseases or mistaken for "normal" effects of aging. Indeed, the risk of hypothyroidism rises with age. Twenty percent of people older than 75, most of them women, lack sufficient levels of thyroid hormone that, among other problems, can cause symptoms of confusion commonly mistaken for dementia.

Symptoms of an overactive thyroid, or hyperthyroidism, include weight loss, increased appetite, anxiety, insomnia and heart palpitations, including atrial fibrillation, a risk factor for stroke. Yet, as with too little thyroid hormone, older people may lack obvious symptoms and remain undiagnosed.

Complete tests for thyroid function include three measurements: for the hormones thyroxine (T4) and triiodothyronine (T3) produced by the thyroid itself, and for thyroid-stimulating hormone (TSH or thyrotropin) produced by the pituitary gland to regulate the thyroid.

Overproduction or underproduction of thyroid hormone afflicts as many as 20 million Americans, including a disproportionate number of women and the elderly. An estimated 1 in 5 women ages 60 and older have some form of thyroid disease.

According to Dr. Jeffrey Mechanick, an endocrinologist affiliated with the Icahn School of Medicine at Mount Sinai in New York, "Unfortunately, older adults experience fewer of the typical signs and symptoms associated with thyroid disorder. This can make diagnosis difficult."