DENVER: Libertarian presidential candidate Gary Johnson, a triathlete who has climbed Mount Everest, released a letter Friday from his doctor declaring him "extremely physically fit" with no medical issues.

Johnson's campaign released the letter from Dr Lyle B Amer of Santa Fe along with a statement that the former New Mexico governor suffers from Celiac disease, a genetic disorder that causes intolerance to gluten.

The 63-year-old Johnson's stellar medical assessment comes weeks after Hillary Clinton (68), collapsed during a bout of pneumonia, and days after a listless debate performance by Donald Trump renewed Democratic whispers about the 70-year-old GOP nominee's stamina.

The letter does not list Johnson's cholesterol and says Johnson will visit a dermatologist to be screened for skin cancer.

Amer's letter says Johnson exercises for an hour a day - it was two hours daily before he started his campaign. He does not drink alcohol, has no complaints of pain, weighs 172 pounds and has blood pressure of 100/70.

"He is an extremely physically fit and healthy 63-year-old male," Amer wrote. "Obviously his decades of dedication to physical fitness, diet, no drinking and no smoking have paid dividends as far as his extraordinarily good health at this time of his life."