The cost of caring for dementia patients has reached $109 billion annually, exceeding that for heart disease and cancer, and will double by the time the youngest baby boomers reach their 70s, according to a study.

Dementia is characterized by a group of symptoms that prevent people from carrying out the tasks of daily living. Reduced mental function makes it impossible for them to do things like keep track of medications or finances. In more severe cases, patients lose the ability to handle basic tasks like bathing and dressing. Dementia is considered a chronic disease of aging, and there is no cure.

More than five million Americans have the disease, according to the Alzheimer's Association, and that number will rise 40 percent by 2025. Dementia represents a substantial financial burden on society, researchers said in the study, published Thursday in the New England Journal of Medicine.

The goal now is to find treatments for Alzheimer's and other brain disorders. To speed along research, President Obama announced this week a campaign called the BRAIN Initiative, which will spend $100 million beginning in 2014 to map the interactions between brain cells and neurological circuits.

Worse to come

"We need more research into interventions to delay or halt the onset of dementia. Right now, we don't really have anything at all," Michael Hurd, an author of the study and director of Rand Corp.'s Center for the Study of Aging, said in an interview. "The problem is going to grow rapidly."

Medical bills for dementia patients are comparatively small, amounting to 16 percent to 25 percent of the total tally, the report said. By far, the most expensive part of dementia care is the cost of care.

When support from family and friends is given a cost value, the yearly expense of dementia care and treatment doubled to $215 billion in 2010, said the study, funded by the National Institutes of Health. That figure will jump to $511 billion by 2040, as the generation born between 1946 and 1964 become elderly, the report said.

By comparison, the direct cost of treating heart disease, the leading cause of death in the United States, was $102 billion in 2010, the study said, while cancer cost $77 billion.

A cruel mystery

The study, conducted by researchers from Rand Corp. and the University of Michigan, Ann Arbor, estimates 15 percent of people older than 70 have dementia, based on their interviews with 856 out of almost 11,000 participants in the U.S. Health and Retirement Study. They also collected self-reported out-of-pocket costs, nursing-home spending, Medicare claims data, and estimates of hours spent by unpaid volunteers. The annual cost per person was estimated to be $56,290.

Little is known about the causes of many brain disorders, including Alzheimer's, a disease expected to affect 65.7 million people by 2030. There have been 101 unsuccessful attempts to develop a treatment for Alzheimer's disease since 1998, including recent setbacks by Pfizer Inc., Johnson & Johnson, and Eli Lilly & Co., according to the Pharmaceutical Research and Manufacturers of America.

The study "heightens the awareness of the particular problem of Alzheimer's disease that somehow as a nation we're going to have to accommodate for," said Richard Hodes, director of the National Institute of Aging in Bethesda, Md., the arm of NIH that directs Alzheimer's research. "Not just the cost for professionals, but the enormously important hours spent by volunteers out of love, becomes more and more of a challenge when we have fewer and fewer people able to take on that role."