New York|For Many Americans, Depression Is Familiar. Here’s What We Know.

Depression is staggeringly common in the United States, with more than one in four adults reporting having been diagnosed with the condition in their lifetimes. In a given year, more than 8 percent of U.S. adults might report a major depressive episode. And there are more than 500,000 hospitalizations for a depressive disorder each year.

Representative Thomas Kean Jr., a Republican from New Jersey, announced on Tuesday that he had joined the ranks of those who had been hospitalized for depression.

Mr. Kean, 57, said that over the past few months he had come to understand “how long depression had been affecting my life.” During a speech on the House floor in Washington, he provided no details of his treatment.

Some people develop depression for the first time in middle age or older, but the usual age of onset is younger, said Dr. Mark Rapaport, the president of the American Psychiatric Association.

“I’m grateful that the congressperson is able to be forthcoming because this is a treatable disease of the brain, and we need people to know that,” Dr. Rapaport said.

A Safe Environment

Experts cited several reasons why someone might be hospitalized for depression, the most common being if the patient is experiencing thoughts of suicide or self-harm.