The nation is poised to elect one of its oldest presidents, and while age doesn't determine health, it begs the question: How much do we know -- and should we know -- about how physically fit Donald Trump and Hillary Clinton are for the job?

"Age always matters" when it comes to risk for disease, said well-known aging researcher S. Jay Olshansky of the University of Illinois at Chicago, but he cautions that it shouldn't be a litmus test for the presidency.

Trump at 70 would be months older than Ronald Reagan on his election day, and Clinton will have just turned 69.

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Age aside, releasing at least some medical information is an election-season ritual.

Clinton has revealed more of this usually intensely private data than Trump. Each had their own doctor write a letter last year attesting they're in excellent health. Clinton's was nearly two pages and included standard lab test results. Trump's was four paragraphs with few details.

That's a far cry from 2008 when Republican Sen. John McCain, then 71, released more than a thousand pages of medical records to show he was cancer-free and fit to serve as president.

The letter approach isn't enough for some experts, who say an independent panel should assess would-be presidents' health, like the fit-for-flight physicals pilots take. After all, history shows presidents have been adept at hiding frailty: Woodrow Wilson's secret stroke; Franklin D. Roosevelt's severe heart disease during his final campaign; Grover Cleveland even sneaked onto a boat for cancer surgery.

"What have we done to help independently vet those who would lead the most powerful nation on earth? Nothing," bioethicists Arthur Caplan of New York University Langone Medical Center and Jonathan Moreno of the University of Pennsylvania wrote in the Chicago Tribune.

Others say candidates' health habits offer important clues.

"It's not a matter about what illnesses you bring but what's your endurance going to be like, and how do you prepare your body to endure a lot of stress," said Dr. James Dewar, vice chairman of family medicine at the University of Pittsburgh Medical Center. He assessed the candidates' health letters and saw no red flags but wished Trump's contained more information.

The travel, junk food, crowds and questions that are part of campaigns make for "an incredible cardiovascular stress test," said Dr. Michael Roizen, chairman of the Cleveland Clinic's wellness institute.

But over potentially eight years in the White House, "you want them to have mental functioning that is both quick and intact," Roizen added.

With life expectancy at a record high and a generation of more active seniors, older presidential candidates are no surprise. But older age also raises concern about the risk of Alzheimer's disease. Reagan, who turned 70 shortly after his first inauguration, was diagnosed with Alzheimer's several years after leaving office.

There's little way to predict whose brain might falter over time, Dewar said. The best defense: "Regular exercise, adequate sleep and diet are things that we associate with keeping our body and our brain healthy."

What to look for:

-Heart risks. Both candidates report good blood pressure. Trump takes a statin drug to lower cholesterol, although his cholesterol levels weren't revealed, and a daily low-dose aspirin, which doctors often recommend to reduce the risk of heart disease and colon cancer. Clinton had a full cardiac evaluation that found no problems, and reports healthy cholesterol levels.

-Medical history. Clinton's doctor reported she is fully recovered from a 2012 concussion, which led to temporary double vision and discovery of a blood clot in a vein in the space between her brain and skull. Clinton also has experienced deep vein thrombosis, a clot usually in the leg, and takes the blood thinner Coumadin to prevent new clots.

She takes a thyroid hormone replacement for hypothyroidism, antihistamines for seasonal pollen allergies, and vitamin B12.

Trump's doctor said he had an appendectomy at age 10.

-Preventive care. Clinton is up to date on wellness screenings, including a normal colonoscopy, mammogram and gynecologic exam. Trump's doctor mentioned only a normal prostate screening.

-Health habits. Clinton makes time for yoga and brisk walks. Her doctor says she eats lots of fruits and vegetables; she's known for snacking on raw hot peppers for a health boost but occasionally indulges -- like with one of Iowa State Fair's famous pork chops on a stick.

Trump's doctor said he lost about 15 pounds over 2015. Trump loves red meat and once tweeted a photo of himself munching McDonald's. His idea of exercise is a campaign speech.

Trump boasts that he's "not a big sleeper. I like three hours, four hours."

Enough sleep is important not just for focus, but because it's when brain cells do some important health maintenance, Roizen noted. Still, high-powered people sometimes report less sleep; he said it's not clear whether someone who's functioned with less-than-recommended amounts for years needs to change.

Possibly the factor most promising for longevity: Both candidates' parents lived into their 80s and 90s, Olshansky noted.

Olshansky's research found many presidents outlived the life expectancy of their time, likely thanks to wealth and access to top medical care that Clinton and Trump also have.

"We have sufficient information to believe the two of them are both likely to be healthy long enough to survive eight years in office," Olshansky said.