WASHINGTON—President Trump is taking more aspirin than his doctors recommend. He briefly tried wearing compression socks for his swelling ankles, but stopped because he didn’t like them. And he regrets undergoing advanced imaging because it generated scrutiny of his health.

“In retrospect, it’s too bad I took it because it gave them a little ammunition,” Trump said in an interview with The Wall Street Journal on his decision to get a cardiovascular and abdominal scan in October. “I would have been a lot better off if they didn’t, because the fact that I took it said, ‘Oh gee, is something wrong?’ Well, nothing’s wrong.”

Trump, 79, the oldest man to assume the presidency, is showing signs of aging in public and private, according to people close to him. Yet he has at times eschewed the advice of his doctors and scoffed at the medical community’s widely accepted health recommendations, relying instead on what he calls his “good genetics.” Trump and his doctor say he is in excellent health, and aides say he maintains a vigorous schedule.

Trump gets little sleep and has recently struggled to keep his eyes open during several televised events in the West Wing. Aides, donors and friends say they often have to speak loudly in meetings with the president because he strains to hear. Aside from golf, Trump doesn’t get regular exercise, and he is known to consume a diet heavy on salty and fatty foods, such as hamburgers and french fries.

The large dose of aspirin he chooses to take daily has caused him to bruise easily, he said, and he has been encouraged by his doctors to take a lower dose. But Trump has declined to switch because he has been taking it for 25 years. “I’m a little superstitious,” he said in the interview.

“They say aspirin is good for thinning out the blood, and I don’t want thick blood pouring through my heart,” Trump said. “I want nice, thin blood pouring through my heart. Does that make sense?”

Trump denied that he struggles to hear. He also denied falling asleep at recent White House events and said he has always gotten by on little sleep.

The president has sometimes described his medical care inaccurately. He has for weeks said that he underwent an MRI at Walter Reed National Military Medical Center in October. When asked about the procedure by the Journal, Trump and his doctor said he got a different form of imaging: a CT scan.

A CT scan is a faster and more common way to capture detailed images of the body. The MRI is a slower test that is superior for soft tissues.

“It wasn’t an MRI,” Trump told the Journal. “It was less than that. It was a scan.”

Navy Capt. Sean Barbabella , Trump’s doctor, confirmed in a statement to the Journal that Trump had received a CT scan. Barbabella said Trump’s doctors initially told him they would perform either an MRI or a CT scan, and they ultimately decided to do the latter. Barbabella said the CT scan was done “to definitively rule out any cardiovascular issues” and revealed no abnormalities. The White House declined to make Barbabella available for an interview.

White House press secretary Karoline Leavitt said the White House had often referred to the procedure as “advanced imaging” and didn’t address why the president hadn’t corrected the record sooner.

Delicate skin

The president has sought to conceal ailments that have led to speculation about his health, covering bruising on his hand with makeup. In his first term, he played down the severity of his Covid-19 symptoms and declined to disclose that he got a colonoscopy.

His physical signs of aging are becoming more evident to some of his closest advisers. His skin is so delicate that Pam Bondi , now his attorney general, caused his hand to bleed when she nicked him with her ring while giving him a high-five at the Republican National Convention in Milwaukee.

The president has often accused his predecessor, President Joe Biden , who was five months younger than Trump was when he took office, of hiding the extent of his health issues. Biden decided not to seek re-election following a damaging debate in which he stumbled over words and appeared to lose his train of thought. Biden reinforced doubts about his fitness by avoiding unscripted exchanges and relying heavily on a few trusted aides who stage-managed his schedule.

Trump has been almost omnipresent in his second term, fielding questions from journalists sometimes several times a day, delivering impromptu remarks and regularly hosting dinners at the White House. Trump veers from topic to topic in his lengthy public statements, and sometimes makes factual errors.

Barbabella said in the statement to the Journal that Trump is in “exceptional health and perfectly suited to execute his duties as Commander in Chief.” The White House provided the Journal with a summary of a Mayo Clinic AI-assisted analysis of Trump’s electrocardiogram that estimated the president’s cardiac age to be that of a 65-year-old.

“As a clinician, you look for clues in people, even if they’re not your patient, and he is just with it on some fairly complex topics,” Mehmet Oz , a physician who serves as administrator of the Centers for Medicare and Medicaid Services, said in an interview with the Journal. Oz hasn’t provided medical care to Trump.

“I can’t even think of a single time where he said something where I don’t think he understands the issue here,” said Oz, who has frequently attended events with Trump. “He may want you to do something that is, you know, is arguable whether it’s the right path to go, but it’s a very rational approach to it.”

An impromptu interview

In an impromptu phone interview that came after the Journal shared details about its reporting with the White House, the president expressed irritation about the public debate over his health. He has grown upset with his own White House staff for not promoting him as more vigorous. “Let’s talk about health again for the 25th time,” he said at the start of the interview. “My health is perfect,” he added.

Trump said he often begins his day early at an office in the White House residence before coming downstairs around 10 a.m. and working in the Oval Office until 7 p.m. or 8 p.m. The White House provided a private calendar for the first 19 days in December, which included hundreds of meetings and phone calls with staff, CEOs, lawmakers and cabinet secretaries.

He said he had asked his staff to modify his schedule so that he can have fewer, more important meetings that he can devote more attention to—a change he doesn’t attribute to age, but to using his time more efficiently. Administration officials said they haven’t yet pared down his meeting schedule.

Trump’s staff have encouraged him to slow his pace. They urged him to spend roughly two weeks in South Florida around Christmas and New Year’s Eve, according to aides, a recommendation he acted on.

Trump’s staff have also counseled him to try to keep his eyes open during public events, fearing the optics of his appearing to fall asleep, a person familiar with the matter said. Cameras caught him appearing to doze in December at a cabinet meeting and during a November announcement about reducing the cost of weight-loss medication .

In mid-July, Trump went to see his doctors at Walter Reed owing to what his physician described as “mild swelling in his lower legs.” Ultrasounds of his veins showed that the president has “chronic venous insufficiency,” according to a memo. It is a common condition among older people in which one-way valves inside the veins don’t work properly, which makes it harder for blood to travel up the legs to the heart.

In the statement to the Journal, Barbabella said the president’s condition is “superficial chronic venous insufficiency,” which involves the smaller veins in the body and doctors say is treatable.

To help treat it, the president briefly wore compression socks. But the socks didn’t stay on for long. “I didn’t like them,” Trump said during the interview.

Trump and his aides said the swelling in his legs has improved. The president said he is getting up from his desk and walking around a bit more, another common way to improve lower-leg swelling.

Exercise is ‘boring’

But he isn’t interested in an exercise routine other than golf. “I just don’t like it. It’s boring,” Trump said. “To walk on a treadmill or run on a treadmill for hours and hours like some people do, that’s not for me.”

Trump takes rosuvastatin and ezetimibe to control his cholesterol and uses mometasone cream to treat a skin condition, his doctor reported in April.

Barbabella, Trump’s physician, said the president uses aspirin for “cardiac prevention.” He said Trump takes 325 milligrams of aspirin a day. A low dose of aspirin is most commonly 81 milligrams, according to the Mayo Clinic.

“They’d rather have me take the smaller one,” Trump said. “I take the larger one, but I’ve done it for years, and what it does do is it causes bruising.”

Of the incident in which Bondi caused his hand to bleed, Trump said, “The ring hit the back of my hand, and, yes, there was a slight little cut,” Trump said. The cut alarmed some who witnessed the exchange, according to a person with knowledge of the episode. It is one of several instances in which his hand has been cut, aides said.

Trump said he applies makeup to his hands after he gets “whacked again by someone.” He added: “I have makeup that’s, you know, easy to put on, takes about 10 seconds.”

The president has difficulty sleeping well at night, and by his own account is often texting and calling aides at 2 a.m. or later. Several allies described getting text messages from him after he catches up on their Fox News appearances in the wee hours of the morning.

“I’ve never been a big sleeper,” Trump said.

Sleeping is a particular issue aboard Air Force One, where Trump keeps his advisers awake, according to aides. Top staff take turns sitting with him on long trips, rotating so that others can sleep while one person remains by his side, according to White House officials. The president is known to poke fun at aides for falling asleep.

Trump said he didn’t fall asleep during recent events at the White House. “I’ll just close. It’s very relaxing to me,” he said in describing shutting his eyes. “Sometimes they’ll take a picture of me blinking, blinking, and they’ll catch me with the blink.”

Oz was at the Oval Office presentation in November and said he believed Trump became bored. Susie Wiles , the White House chief of staff, and others have urged cabinet members to shorten their presentations, according to administration officials.

When asked about his hearing, Trump grew sarcastic. “I can’t hear you. I can’t hear you. I can’t hear a word you’re saying,” he said mockingly. The president said he only sometimes struggles to hear “when there’s a lot of people talking.”

At times the president has had trouble hearing questions from reporters that others heard. During a dinner in September with heads of major technology companies, Trump took questions from the press and motioned with his hand for a reporter to speak up. The journalist asked if Trump planned to speak soon with Russian President Vladimir Putin .

“What did—? What?” Trump said. Then he leaned toward his wife, Melania, who repeated the question to him, her comments captured on his microphone. Leavitt said such incidents are rare.

Barbabella described the president’s hearing as “normal” and said in a statement to the Journal that Trump doesn’t require a hearing aid.

Trump said he hasn’t made changes to his diet. In a podcast interview in October, Republican National Committee Chairman Joe Gruters described being shocked by Trump’s eating habits when they traveled together during the campaign. While flying to a campaign event, according to Gruters, Trump consumed french fries, a McDonald’s Quarter Pounder hamburger, a Big Mac and a Filet-O-Fish.

Trump said he had plenty of energy, which he credited to his parents, who he said were energetic until their old age.

“Genetics are very important,” he said. “And I have very good genetics.”

Write to Annie Linskey at annie.linskey@wsj.com , Josh Dawsey at Joshua.Dawsey@WSJ.com and Meridith McGraw at Meridith.McGraw@WSJ.com