Her countdown, a hybrid of mental calisthenics and magic spell, has become a daily ritual to ward off Alzheimer's disease. So has gobbling handfuls of vitamins and forcing herself to keep an almost ceaseless vigilance against memory lapses. Every day, she counts backward by sevens.

100, 93, 86 . . .

If nothing else, the numbers exercise offers a little reassurance that so far, she has not begun traveling the path that her mother went, and she is not going where her husband, Ed, is going now.

"I think, 'Oh my gosh, if he's got it, I could get it,' " she said. "My daughters are worried."

Like thousands of others whose parents and other relatives have developed Alzheimer's, Featherstone, 65, of Arlington said she fears that she will be next. Having seen loved ones who seemed to vanish from within as the disease ran its course, many people close to Alzheimer's disease have decided to do whatever they can to keep from getting it.

They avoid antiperspirants and kitchen utensils that contain aluminum. They gulp fistfuls of pills loaded with vitamin E, Ginkgo biloba, coenzyme 10, biotin, folic acid or antioxidants. They take up musical instruments and learn foreign languages. They work crossword puzzles as if solving each clue could save a life.

"They're all afraid. They're so fearful of the dire consequences of Alzheimer's," said Betty Ransom, program director at the Alzheimer's Association's National Capital Area chapter.

Many have embarked on a variety of regimens, from the commonplace to the extreme, from those supported by clinical studies to others based on Internet rumor.

Some go so far as to seek costly testing that can reveal whether their genetic makeup makes them susceptible to a form of the disease that strikes early. Some leave the country for such exotic and unproven therapies as chelation therapy, a treatment that introduces chemicals into the body that bind with heavy metals. The treatment is used in severe lead poisoning and has been touted, despite studies showing no proof of efficacy, as a preventive measure against heart disease and Alzheimer's.

Ransom, who teaches the course "Brain Aerobics: Use It, or Lose It," encourages senior citizens to engage in relatively simple exercises for at least 10 minutes a day to help keep their minds nimble. Doing crossword puzzles and even watching such game shows as "Jeopardy!" are useful, she said. But as the disease becomes more widespread and discussion about Alzheimer's moves from the shadows, younger and younger people are expressing fears of developing it.

"It's not uncommon to see an adult child who's maybe in their thirties or forties, saying, 'Oh boy, this must mean I'm going to have a bigger chance of getting this,' " Ransom said. "And they're bound to think like that. I would."

Even some people who are fatalistic and resigned to the notion that nothing will help admit to taking precautions.

"I don't really think there's anything you can do," said Viola Miller, whose 97-year-old mother has been found to have Alzheimer's. "I could easily get cancer. I could easily get a heart condition. I could also get hit by a car. You can sit around and worry yourself to death before the disease gets you."

After all, Miller said, her mother lived as clean a life as anyone could: no smoking, no alcohol and no drugs, with the possible exception of old-fashioned cold remedies.

"It was a rarity if she took an aspirin," Miller said.

Also, in contrast to studies suggesting that low educational achievement and social isolation could be linked to Alzheimer's, her mother remained socially and mentally active until the disease attacked, Miller said.

That said, Miller said she avoids aluminum pots and pans.

About 4 million people have Alzheimer's, and some 360,000 new cases are diagnosed every year, according to the National Institute on Aging. That number is expected to rise as the population ages, the institute says.

The Food and Drug Administration has approved four drugs to treat or slow the progress of Alzheimer's disease, but only three are generally used. All attempt to boost the level of a chemical in the brain that is linked to memory, said Neil Buckholtz, chief of the Dementias of Aging Branch of the National Institute on Aging.

Most therapies focus on the cognitive effects, although doctors have taken more interest in recent years in treating behavioral problems associated with dementia, such as wandering, aggression or agitation. Scientists, both in academia and in the pharmaceutical industry, are searching for preventive drugs. Among the areas they are looking at is whether estrogen, vitamin C, vitamin E or antioxidants can play a role in halting the disease.

"The direction that we're going [in] is to try to prevent the disease or delay the onset or delay the progress of the disease," he said.

Estrogen, for example, does not seem to be effective in delaying the progression of Alzheimer's. Scientists are still trying to learn whether the hormone can prevent the disease's onset.

Anti-inflammatory drugs also are under study. Epidemiological studies suggest that statins -- anticholesterol drugs such as Zocor -- and drugs that lower the levels of an amino acid called homocystine also might lower the risk of contracting Alzheimer's. And scientists are searching for drugs that might target chemicals linked to the buildup of the telltale plaques and tangles that choke off nerve cells.

"But nothing at this point has come out definitive on any of these," he said. "Other than the drugs that are actually approved at this point by the FDA, there's nothing out there that we can tell people: 'This is has been approved. You can take this.' "

Yet many people, building on studies that suggest vitamin E or Ginkgo biloba might have beneficial effects, have changed their habits to avoid the disease. As for aluminum, there is no definitive link to the disease, Buckholtz said. But many people rid their kitchens of it just the same.

"The 50-year-olds -- they are the ones who start to worry," said Lin Noyes, clinical director for the Alzheimer's Family Day Center in Falls Church.

Amy Fadida, a high-tech executive who lives in the District, said she was horrified by the progression of the disease in her mother, a smart, vivacious, playful woman who seemed to Fadida like a Jewish version of "I Love Lucy" star Lucille Ball. Signs of trouble multiplied slowly in her mother's life: The woman who prided herself on her appearance suddenly came to the door with smeared lipstick. Conversations over the most ordinary matters trailed off in ellipses. Her mother became lost easily on her way to Fadida's, and later, she got lost going home. She became ever more easily confused and then vacant.

"I hated seeing how it turned this woman who everybody knew as a bright light -- this vivacious, full-of-life woman -- into just an empty being," Fadida said. "It was probably as I saw her changing that it really hit me what this meant: that I thought, 'Oh my God, I'm not even 50. I'm going to spend the next 15 years of my life being the primary caretaker . . . for this woman, and then she'll finally die, and then I'll have it. That was really the first time I got this overwhelming sadness and fear that this is the beginning of the end for me, too."

After her mother's death, Fadida unsuccessfully tried to arrange for an autopsy -- the only way to definitively diagnose Alzheimer's -- because she wanted to know with certainty the cause of her mother's dementia. She adopted a regimen of exercise and vitamins to protect herself and even laid out $850 in out-of-pocket fees at Inova Fairfax Hospital for a "wellness scan" of her brain and other organs. The scan, similar to an MRI, gave her a clean bill of health. Even so, she said she frets whenever she misplaces objects or forgets something, however much such lapses might be easily explained by her punishing schedule at work.

"It's like in my peripheral vision or something, but it eats away at me that maybe it's not just cognitive overload, maybe it's not that I work 18 hours a day, maybe it's that this is very early signs of this disease," she said. "I drive doctors nuts."

Donald M. "Mike" Showers, 50, of Leesburg, whose mother, Sarah, died of Alzheimer's, is fatalistic. In his view, it's a matter of genetic roulette.

"I've never worried about it," he said.

Showers has, however, considered undergoing genetic testing, even though if he tested positive for a predisposition to Alzheimer's, it could cause his insurance company to discontinue coverage. The test's greatest value, he said, might be advising loved ones of the results so that they could understand what's happening if the symptoms develop and make preparations for his care.

His brother David Showers, 47, banished aluminum from his life, refusing even to drink from aluminum cans. "I stopped using antiperspirant because it contains aluminum chlorhydrate," he said.

Hattiejane Darracott, 60, believing that therapies based on magnetic fields have improved her general health, has applied them to her brain. She said she is hoping that she can avoid developing Alzheimer's, which her mother has.

Darracott, a nurse and massage therapist who left the District to live with her mother in Falls Church, said her fear of Alzheimer's is compounded every time she searches for a word she should know. While watching TV or lying in bed, she waves a Japanese-made magnetic device around her head as if using a blow dryer.

Though she does not necessarily believe in a miracle cure, she reasons that the magnetic therapy can't hurt, she said, and she believes she has seen improvements already.

"If it helps lower the odds -- great."