Trump's doctor says he's in excellent health - but are US presidents' health checks a PR exercise?

Any concerning health issues the American public should know about, Mr President?

"Well, they think I look too young," Joe Biden, then aged 81, joked after his annual medical check-up as the oldest president in US history.

The US president is one of the most powerful people on the planet - and the public scrutiny of their health records has grown into a distinctly American phenomenon.

Every president in modern history has taken the short journey from the White House to Walter Reed National Military Medical Center for a regular physical exam - and it's as much about political messaging as it is about health.

"Americans historically have wanted masculine presidents, vigorous presidents," said Dr Matt Dallek, a political historian at George Washington University.

The physical exam is one way a president can outwardly demonstrate his own vitality and therefore project a sense of political power. It is something Donald Trump, just under three weeks shy of his 80th birthday, has sought to make central to his own image as president.

After his annual exam, the White House released a memo on Friday from Trump's doctor, who said he was in "excellent health", but did recommend he exercise more and lose weight.

He also noted the president had "strong cardiac, pulmonary, neurological and overall physical function" and was "fully fit to carry out all duties of the commander-in-chief and head of state".

But even an assurance of a clean bill of health by the president's doctor only goes so far. There is no requirement for the president to share their medical records and they are protected by the same health privacy law as every other American.

Before the advent of television, it was much easier for presidents to disguise their health struggles.

In 1919, President Woodrow Wilson suffered a major stroke that left him mostly incapacitated for the final stretch of his presidency, effectively leaving his wife to make decisions for over a year. The severity of his condition was largely covered up by his physician and other staff.

Later, while the public was somewhat aware that President Franklin D Roosevelt lived with paralysis from polio, the White House downplayed his use of a wheelchair until his death in office in 1945.

Jacob Appel, a medical ethicist at New York's Mount Sinai Hospital and a presidential health historian, said it wasn't until President Lyndon B Johnson's term during the Cold War in the 1960s that results of regular physicals were announced to the public.

In the 1970s, President Gerald Ford insisted on making some of his medical information pu