The US president was speaking from prepared notes as he announced a plan to look at the country's libel laws at a White House Cabinet meeting.
Press secretary Sarah Sanders has said the White House will provide a "readout" of the exam after it's completed.
He was certainly the oldest, when he moved into the White House a year ago aged 70.
Michael Wolff, author of 'Fire and Fury: Inside the Trump White House, ' has claimed that Donald Trump lacked the mental fitness to serve as president, describing him as an "undisciplined man-child" who did not want to win the election.
GETTY TURNING POINT Donald Trump's first physical exam could be a major event
"Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart. So we're going to take a strong look at that", he said Wednesday.
Mr Trump will fly on Friday to the Walter Reed National Military Medical Centre in Bethesda, Maryland, for his annual exam.
Donald Trump's White House doctor says, "The President is in excellent health". Assessment of cognitive function is not purely subjective, but objective as well. "They get out of the military, and they had nobody to talk to, nobody to speak to".
Trump himself mocked the claims, proclaiming himself a "very stable genius" who won the presidency on his first try.
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An estimated 65,000 teens who are DACA recipients, or are eligible for the program, graduate from high school each year. The organization, which is less than four years old, says this is the largest grant it has ever received.
During the 2016 presidential campaign, Trump's physician released a summary of his health that included his height, weight (236 pounds), cholesterol (HDL 63, LDL 94, triglycerides 61), blood pressure (116/70), blood sugar (99) and results of liver, thyroid, heart and colon exams. The one-page letter stated Trump's testosterone level, 441.6, was in the normal range, as were his PSA reading for prostate abnormalities and tests of his liver and thyroid. Bandy X. Lee. That briefing was provided although both the American Psychiatric Association and the American Psychological Association advise that mental health professionals should not offer a judgment about anyone, including public figures, who they haven't personally examined.
Trump has a lot to feel good about as he faces the examination. In a series of interviews a year ago, Trump showed journalists how he summons a butler to bring him a soda by pressing a red button on his Oval Office desk.
Trump is open about his unhealthy eating habits, posting a photo of himself aboard his campaign plane with a bucket of fried chicken, bragging about the chocolate cake at his Mar-a-Lago resort, and drinking Diet Coke around the West Wing. A typical report from President Obama's or President Bush's physicals summarized their test results and pronounced the leaders healthy and likely to remain so for the duration of their time in office.
A smiling President Trump said: "It better go well, otherwise the stock market will not be happy".
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Market participants were awaiting a US decision on whether to extend temporary waivers on sanctions against Iran due on Friday. Brent was trading below $30 in early 2016 as a result of a massive supply glut and weaknesses in the world economy.
Neither measure has advanced in Congress. And he once said he had a full day of meetings when he was in fact playing golf.
Right after he became president Trump insisted he drew a larger inauguration crowd than Barack Obama's first ceremony in 2009.
But Barbara Perry, director of presidential studies at the University of Virginia's Miller Center, highlighted how past presidents were adept at "hiding their medical infirmities".
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In addition, the vaccine included DNA for a protein that is highly conserved and, thus, shared across different strains of virus. The CDC says the vaccine can reduce your risk by as much as 60 percent if the circulating virus is close to the vaccine virus.