In 1960, Joan Levin, 15, took a test that turned out to be the largest survey of American teenagers ever conducted. It took two and a half days to administer, and included 440,000 students from 1,353 public, private and parochial high schools around the country - including Parkville Senior High School in Parkville, Maryland, where she was a student.

"We knew at the time that they were going to follow up for a long time," Levin said - but she thought that meant about 20 years.

Fifty-eight years later, the answers she and her peers gave are still being used by researchers - most recently in the fight against Alzheimer's Disease. A study released this month found that subjects who did well on test questions as teenagers had a lower incidence of Alzheimer's and related dementias in their 60s and 70s than those who scored poorly.

Known as Project Talent, the test was funded by the U.S. government, which had been concerned, given the Soviet Union's recent successful Sputnik launch, that Americans were falling behind in the space race.

Students answered questions about academics and general knowledge as well as their home life, health, aspirations, and personality traits, and the test was intended to identify students with aptitude for science and engineering. Test-takers included Janis Joplin, then a senior at Thomas Jefferson High School in Port Arthur, Texas, and Jim Morrison, then a junior at George Washington High School in Alexandria, Virginia.

In recent years, researchers have used Project Talent data for follow-up studies, including one published Sept. 7 in the Journal of the American Medical Association. Conducted by researchers at the Washington-based American Institutes for Research, the organization that originally administered the test, it compared results for over 85,000 test-takers with their 2012-2013 Medicare claims and expenditures data and found warning signs for dementia may be discernable as early as adolescence.

The study looked at how students scored on 17 areas of cognitive ability such as language, abstract reasoning, math, clerical skills, and visual and spatial prowess, and found that people with lower scores as teenagers were more prone to getting Alzheimer's and related dementias in their 60s and early 70s.

Specifically, those with lower mechanical reasoning and memory for words as teens had a higher likelihood of developing dementia in later life: Men in the lower-scoring half were 17 percent more likely, while women with lower scores were 16 percent more likely. Worse performance on other components of the test also showed increased likelihood of later-life dementia.

An estimated 5.7 million Americans have Alzheimer's, and in the absence of scientific breakthroughs to curb the disease, the Alzheimer's Association projects that number could reach 14 million by 2050, with the cost of care topping $1 trillion per year.

The 1960 test could have the potential to be like the groundbreaking Framingham study, a decades-long study of men in Massachusetts that led to reductions in heart disease in the 1970s, 80s, and 90s, said Susan Lapham, director of Project Talent and a co-author of the JAMA study.

"If Project Talent can be for dementia what the Framingham study was for heart disease, it will make a difference in public health," she said. "It indicates that we should be designing interventions for kids in high school and maybe even earlier to maybe keep their brains active from a young age."

This might include testing children, identifying those with lower scores, and "getting them into a program to make sure they're not missing out and maybe putting themselves at risk," she said.

For years, little was done with the Project Talent data because the participants couldn't be found. A proposal in the 1980s to try to find them failed because, in that pre-Internet age, the task seemed too daunting.

In 2009, as the students' 50th high school reunions were coming up, researchers decided to use the reunions as an occasion to reach out to many of them (about a quarter have died). They were then able to use the test data to study things like the effects of diabetes and personality type on later life health.

But when contacted, the outcome participants were most interested in was dementia, said Lapham. "They wanted that to be studied more than any other topic," she said. "They said, 'The thing I fear most is dementia.'"

While students were supposed to have received their results soon after taking the test, some students said they didn't remember getting them.

Receiving her results recently was interesting in hindsight, said Levin, a retired human resources director who is now 73 and living in Cockeysville, Maryland. Most of her scores were over 75 percent, with very high marks in vocabulary, abstract reasoning, and verbal memory, and lower marks in table reading and clerical tasks.

Low scores don't mean a person will necessarily get dementia; the correlation is merely associated with a higher risk. But even if her scores had been lower, Levin said she would want to know. "I'm kind of a planner and I look ahead," she said. "I'd want my daughter and her family to maybe have an idea of what to expect."

Karen Altpeter, 75, of Prescott, Wisconsin, also said she would also probably want to know about her risk, since both her mother and grandmother had Alzheimer's. She liked the idea that the answers she had given as a teen could help science.

"If there's any opportunity I can have to make a difference just by taking a test and answering some questions, I'll do it," she said. "I want the opportunity to make things better for people."

Earlier studies had suggested a relationship between cognitive abilities in youth and dementia in later life, including one that followed 800 nuns earlier in the 20th century and found that the complexity of sentences they used in writing personal essays at 21 correlated with their dementia risk in old age.

But that study included only women, and no minorities. Project Talent's subjects reflected the nation's demographic mix in 1960.

Today, however, the country is more diverse. The number of minorities 65 and over is projected to grow faster than the general population, and by 2060, there will be around 3.2 million Hispanics and 2.2 million African Americans with Alzheimer's disease and related dementias, according to a CDC study published this week. African-Americans and Hispanics both have higher prevalence of Alzheimer's and related diseases than non-Hispanic whites.