New research shows that a milder type of mental decline that often precedes Alzheimer's disease is much more common than thought.

Nearly a million older Americans slide from normal memory into mild impairment each year, doctors reported Monday at a medical conference in Chicago. That's in addition to the half million Americans who develop full-blown Alzheimer's or other forms of dementia.

The problem is sure to grow as Baby Boomers age. Dr. Ralph Nixon, a New York psychiatrist and adviser to the Alzheimer's Association, was blunt. "We're facing a crisis," he said.