Washington DC - President Donald Trump on Friday touted his "perfect health" and cognitive skills amid persistent questions over the 79-year-old's fitness for office.

"The White House Doctors have just reported that I am in 'PERFECT HEALTH,' and that I 'ACED' (Meaning, was correct on 100% of the questions asked!), for the third straight time, my Cognitive Examination, something which no other President, or previous Vice President, was willing to take," Trump claimed on Truth Social.

The Wall Street Journal on Thursday published an interview with Trump – who is the oldest person to assume the US presidency – in which he blamed aspirin for large bruises on his hand and denied falling asleep during meetings.

Trump also changed his previous statement about receiving an MRI scan in October, saying it was instead a quicker CT scan.

Despite basing much of his political image on projecting vigor, the first year of Trump's second term in office has been dogged by growing questions.

His right hand shows persistent bruising, often covered with thick makeup and at times a bandage, and his ankles have appeared swollen.

On occasion, Trump has clearly struggled to keep his eyes open, including during an Oval Office meeting with health representatives in November.

Trump told the Journal that he wasn't dozing, just relaxing.

"I'll just close. It's very relaxing to me," he said. "Sometimes they'll take a picture of me blinking, blinking, and they'll catch me with the blink."

In his post on Friday, Trump added that any presidential or vice presidential candidate should be required to take a "strong, meaningful, and proven" cognitive exam.

"Our great Country cannot be run by 'STUPID' or INCOMPETENT PEOPLE!" he wrote.