Suicide rates among middle-aged Americans have increased drastically in recent years, but the reason remains a mystery to public health officials, The New York Times reported.

A five-year analysis of the nation’s death rates released by the Centers for Disease Control and Prevention found that the suicide rate among 45- to 54-year-olds increased 20 percent from 1999 to 2004, a larger increase than any other age group during the same period, The Times reported.

In contrast, the suicide rate for 15- to 19-year-olds increased less than 2 percent during the same period, and it decreased among people 65 and older, according to the report.

Researchers said they are baffled by the suicide spike among those in midlife. The lack of concrete research has given rise to different theories, including a sudden drop in the use of hormone-replacement therapy by menopausal women after health warnings in 2002, higher rates of depression among baby boomers or a simple statistical fluke, The New York Times reported.

Experts told The Times that news attention and prevention resources typically have focused on the young or very old, leaving middle-aged people without a national support system.

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