The rate of dementia among people 90 or older will reach epidemic proportions as the number of extremely elderly individuals continues to climb, according to the recently published results of “The 90+ Study.”

The study is one of the few in the United States that samples large numbers of centenarians and tracks the rate of all forms of dementia from age 90 onward. The University of California researchers discovered that incidence rates of dementia roughly double every five years. From age 90 to 94, the rate was 12.7% per year. Those aged 95 to 99 had an incident rate of 21.2% per year, while the 100+ crowd had a rate of 40.7% per year, according to the study.

Prior to 2007, the year follow-up testing for the study ended, there were roughly 2 million seniors aged 90 or older in the U.S. That number is expected to mushroom to 8.7 million by 2050, according to some estimates, dramatically increasing the number of very old seniors with dementia, researchers say. The study appears in the February issue of Annals of Neurology.