ABC News’ Mikaela Conley reports:

Nearly three-quarters of the 36 million people living with dementia have not been diagnosed with it, according to a new report sponsored by Alzheimer’s Disease International.

Experts say the lack of diagnosis has enormous repercussions on early treatment and care, and has a direct impact on the disease’s cost  to society.

“ Early diagnosis and intervention is good for people with dementia, their caregivers and society as a whole,” said Dr. Sube Banerjee, a professor of mental health and aging at King’s College London and co-author of the report. “The bad news is that there are lots of people who do not benefit from early treatment and care because they are simply diagnosed too late.”

Treatment gaps are prevalent worldwide, said Banerjee, and because of this, countries should make dementia a national health priority by generating response strategies and policies to manage it.

“It’s so important to have good quality dementia care because there is a dependence that happens and patients stay dependent, so it’s important for countries to have long-term strategies,” Banerjee said.

The global cost of Alzheimer’s disease and associated dementias reached an estimated $600 billion last year, according to Alzheimer’s Disease International, and the cost constitutes about 1 percent of the world’s domestic product, or 1.5 percent of the U.S. GDP.  If dementia were a country, its economy would rank No. 18 in the world, according to the report. And those numbers will spike even higher, as the illness is expected to increase three-fold by 2050.

“Knowledge is power here,” Banerjee said. “But you can’t access care if you don’t know what you have.”

While early medical intervention can slow the progression of the disease, there are also smaller, simpler options that can go hand-in-hand with treatment.  Peer and support groups allow patients and caregivers to share solutions and  treatment options at early diagnosis.  Studies have found  that patients and their families benefit from such  help and support  in the  early stages of diagnosis, the authors said.

“There are those beliefs out there that dementia is  just a natural part of aging, but it’s not,” said Banerjee. “It’s a nasty, horrible illness. We can’t make it go away right now, but we can make life with it much better if they’re diagnosed early.”