Barack Obama's former physician has said Joe Biden 'is not a healthy guy' after the 77-year-old released a doctor's letter claiming he is 'fit to be president'.

Dr David Scheiner, 81, said he is worried about Biden's risk of a stroke after the letter disclosed he is taking cholesterol medication and has an irregular heartbeat, having previously suffered aneurysms.

Dr Scheiner, who treated Obama for 22 years before he became president, added that he would like to see the results of an MRI or CT scan, which were not included.

Scheiner said he would also like to review the results of a sleep study, given Biden had operations on his nasal passages to treat sleep apnea.

Dr David Scheiner, 81, has cast doubt on Joe Biden's health records - saying he is at risk of a stroke, despite a letter earlier this week claiming he is 'fit to be president'

Speaking to the Washington Examiner, he said: 'He's not a healthy guy. He's not in bad shape for his age, but I wouldn't say he's in outstanding health.

'Could I guarantee he won't have issues for the next four years? He has a lot of issues that are just sort of sitting there.'

According to the doctor's report released Tuesday by the 77-year-old former vice president, Biden is 'healthy, vigorous' and 'fit to successfully execute the duties of the Presidency.'

Dr. Kevin O'Connor, who has been Biden's primary care physician since 2009, wrote in a three-page note that the Democratic presidential candidate is in overall good shape - he's trim, exercises and keeps his cholesterol at healthy levels with the use of a statin medication.

Since 2003, Biden has had episodes of atrial fibrillation, a type of irregular heartbeat that's potentially serious but treatable.

Dr Scheiner said an MRI or CT scan should have been included with the report, but wasn't

His doctor now describes the atrial fibrillation as 'persistent.' O'Connor cited a list of tests that show the candidate's heart is functioning normally and his only needed care is a blood thinner to prevent the most worrisome risk, blood clots or stroke.

Another Democratic candidate, Michael Bloomberg, has the same kind of irregular heartbeat, according to records released last week.

Biden had a brush with death in 1988, requiring surgery to repair two brain aneurysms -- weak bulges in arteries, one of them leaking. Biden has never had a recurrence, his doctor said, citing a specific test in 2014 that examined his arteries.

O'Connor's letter cited only a few other minor ailments. Biden takes medications, as needed, for seasonal allergies and occasional reflux, or heartburn. He has had several small, non-melanoma skin cancers removed over the years. Preventive screenings, including colonoscopies, show no signs of trouble.

'Overall he's in good health,' said Dr. Mary McLaughlin, director of cardiovascular health and wellness at Mount Sinai Heart in New York, who reviewed Biden's information.

She noted that he has good blood pressure without needing medication, unusual for his age, and that he exercises five days a week.

'I would say that someone with well-controlled atrial fibrillation on a blood thinner definitely can perform the duties of a stressful job,' McLaughlin added. But she questioned why the records don't mention a cardiac stress test, which would eliminate any questions about heart function.

Biden is the third Democratic presidential candidate to release his medical records. Massachusetts Sen. Elizabeth Warren, 70, released a doctor's note earlier this month that said she is in 'excellent health.' A letter from Bloomberg's physician said the 77-year-old New York billionaire was in 'outstanding health.'

JOE BIDEN'S MEDICAL NUMBERS Kevin O'Connor, director of executive medicine at George Washington Medical Faculty and a former WHite House doctor has been Biden's physician since 2009 Age: 77 Height: 5ft 11.65ins Weight: 178lbs Body Mass Index: 24.38 (healthy range is 18.5 to 24.99) Blood pressure: 128 over 84 - pre-high blood pressure Total cholesterol: 126mg/dL LDL ('bad') cholesterol: 69mg/dL('optimal') HDL ('good') cholesterol: 36mg/dL ('high risk for heart disease') Blood sugar: 81 mg/dL (normal) Medications: Apixaban (Eliquis) for anticoagulation; rosuvastatin (Crestor) for cholesterol; esomeprazole (Nexium) for acid reflux; fluticasone/azelastine (Dymista) and fexofenadine (Allegra) for seasonal allergies Exercise regimen: Attempts to walk seven miles a day, 'I don't always hit it.' Tobacco: Has never smoked Drugs: Never used Alcohol: Does not drink Medical history: Brain surgery after bleeding aneurysm, in 1988, which also repaired another aneurysm, but was followed by deep vein thrombosis and pulmonary embolism. Medication then surgery for Benign Prostatic Hyperplasia; cleared of prostate cancer. Gallbaldder removed in 2003. Sinue and nasal passage surgeries. Mild diverticulosis and non-cancerous tubular adenoma found during colon exams. Several localized non-melanoma skin cancers removed Advertisement

Bernie Sanders, the oldest candidate in the field at 78 years old, said that he'd release his records 'probably by the end of the year.' He suffered a heart attack in October that took him off the campaign trail for a few days.

Biden, Sanders and Bloomberg would be the oldest president in history if elected.

Republican Donald Trump, now 73, was the oldest newly inaugurated first-term president.

He has been criticized for releasing only cursory details on his health while running for the White House.

But he has also mocked Biden, suggesting age has slowed his potential Democratic rival.

What is atrial fibrillation? Atrial fibrillation is a heart condition that causes an irregular and often abnormally fast heart rate. A normal heart rate should be regular and between 60 and 100 beats a minute when you're resting. You can measure your heart rate by feeling the pulse in your neck or wrist. In atrial fibrillation, the heart rate is irregular and can sometimes be very fast. In some cases, it can be considerably higher than 100 beats a minute. This can cause problems including dizziness, shortness of breath and tiredness. Advertisement

Biden's age has been a lingering shadow on his candidacy, even with other septuagenarians in the race.

In one summer debate, Julian Castro suggested, wrongly, that Biden had forgotten details of his own health care proposal. Castro, now 45, denied he was taking a shot at Biden's age, though that's how it was widely interpreted.

Earlier this month in Iowa, a voter who said he was 83 told the candidate he is too old to serve as president. Biden challenged the man to a push-up contest and an IQ test.

None of the recent releases of candidates' health information has mentioned screenings for memory problems, and whether they're needed or useful - or even what kind is appropriate -- in high-functioning adults is an unsettled medical question.

When he brings up the matter himself, Biden acknowledges his advancing age but argues that it comes with the 'wisdom' and 'experience' to manage the hyperpartisan nature of Capitol Hill and calm the international turbulence of Trump's presidency.

The former vice president does have longevity in his family. His father lived to be 86. His mother lived to age 92.

Warren, Sanders and Biden have all showcased their physical activity during the campaign, with Warren frequently jogging to the podium at events and Sanders playing softball with staff.

A Pew Research Center poll from May found that about half of Democrats said it would be best for a president to be in their 50s. A quarter said it would be best for a president to be in their 40s, and 16% preferred a president in their 60s. Just 3% said someone in their 70s would be best - and 6% said the same of a president in their 30s.