ITHACA, N.Y. – When she worked on the trading floor of the Chicago Board Options Exchange, long before cellphone calculators, Susan Saran performed complex math problems in her head. Years later, she was in charge of investigating insider trading deals.

Now she struggles to remember multiplication tables.

Seven years ago, at age 57, Saran was told she has frontotemporal dementia, a progressive, fatal brain disease. "It was absolutely devastating," she said. "I was told to establish myself in a community before I was unable to care for myself."

So Saran uprooted herself. She sold her home in 2015 and found Kendal at Ithaca, a retirement community in rural New York whose website promised "comprehensive health care for life."

And now, she's fighting with that community over her right to determine how she'll die — even though she has made her wishes known in writing. Such a fight could ensnare millions of Americans in coming years. By 2050, nearly 14 million Americans 65 and older may have Alzheimer's diagnoses.

In 2018, after two brain hemorrhages, Saran signed an advance directive for dementia, a controversial new document created by the group End of Life Choices New York that instructs caregivers to withhold hand-feeding and fluids at the end of life to avoid the worst ravages of the disease.

But when Saran submitted the document to Kendal at Ithaca, where she has spent more than $500,000 to secure her future, officials said they could not honor her wishes.

In a letter, lawyers told Saran that the center is required by state and federal law to offer regular daily meals, with feeding assistance if necessary.

It's a cruel quandary for Saran and other Americans who have turned to dementia directives. Even when people document their choices — while they still have the ability to do so — there's no guarantee those instructions will be honored, said Dr. Stanley Terman, a California psychiatrist. "It is, in my opinion, a false sense of security," Terman said.

That may be especially true for the 2.2 million people who live in long-term care settings in the U.S. People with dementia are most likely to die in nursing facilities, said research from Duke University and the Veterans Affairs Boston Healthcare System.

"If you've got the resources, where you've got family and paid caregivers at home, you're all set," said Dr. Karl Steinberg, a California geriatrician and hospice physician. If you're living in a facility, "it's not going to happen."

One key question is whether patients with dementia — or those who fear the disease — can say in advance that they want oral food and fluids stopped at a certain point, a move that would hasten death through dehydration.

It's a form of what's known as VSED — voluntarily stopping eating and drinking — a practice among some terminally ill patients. Many states prohibit the withdrawal of assisted feeding, calling it basic "comfort care" that must be offered. Only Nevada explicitly recognizes an advance directive that calls for stopping eating and drinking.

Critics of such documents, however, say they could lead to forced starvation of incapacitated people. Dr. James Wright, medical director of three long-term care facilities in Richmond, Va., said many people with dementia become content with their situation, even when they never thought they would be.

But Saran said she understood what losing her abilities might mean after her strokes. "I realized, oh, my God, I might get stuck in a situation where I can't take any independent action," she recalled. "I better make sure I have all my paperwork in order."

She was stunned to learn it might not matter. "I thought this was it," she said. "I thought I'd move here and everything was taken care of, everything was settled. And now it's not."