In patients with depression, anxiety and other psychiatric problems, doctors often find abnormal blood levels of thyroid hormone. Treating the problem, they have found, can lead to improvements in mood, memory and cognition.

Now researchers are exploring a somewhat controversial link between minor, or subclinical, thyroid problems and some patients’ psychiatric difficulties. After reviewing the literature on subclinical hypothyroidism and mood, Dr. Russell Joffe, a psychiatrist at the North Shore-Long Island Jewish Health System, and colleagues recently concluded that treating the condition, which affects about 2 percent of Americans, could alleviate some patients’ psychiatric symptoms and might even prevent future cognitive decline.

Patients with psychiatric symptoms, Dr. Joffe said, “tell us that given thyroid hormones, they get better.”

The thyroid, a bow-tie-shaped gland that wraps around the trachea, produces two hormones: thyroxine, or T4, and triiodothyronine, known as T3. These hormones play a role in a surprising range of physical processes, from regulation of body temperature and heartbeat to cognitive functioning.