Alzheimer’s may be No. 3 cause of death in U.S.

Alzheimer’s disease may now be one of the top three causes of death in the United States.

CNN notes that a new study of aging patients suggests that the disease may claim more than half a million lives a year. The disease was blamed for over 83,000 U.S. fatalities in 2010 and was the sixth-leading cause of death. But its actual toll may be six times that now, said Bryan James, an epidemiologist at the Rush Alzheimer's Disease Center in Chicago.

"Death certificates are well known to underreport deaths from Alzheimer's and other types of dementia," said James, who authored the study published Wednesday. "The more immediate causes of death, such as pneumonia or heart attack, are usually listed, and the underlying causes of death are usually left off."

The Alzheimer’s Association states on its website that while deaths from other major diseases, such as HIV/AIDS and strokes, continue to experience significant declines, Alzheimer's deaths continue to increase. And there is no known cure for the disease, which can cause progressive mental deterioration due to generalized degeneration of the brain.

Heart disease and cancer remain the nation’s top killers.