US Vice President Kamala Harris, the Democratic presidential nominee, released a letter from her doctor on Saturday that pronounced her in good health and fit for high office, in an effort to draw a contrast with her counterpart, Donald Trump.

In a memo distributed by the White House, the vice president's physician, Joshua Simmons, said Harris's most recent physical exam in April was "unremarkable," that she maintains an active lifestyle and "very healthy diet" despite a busy schedule, suffers from seasonal allergies and sporadic hives, does not use tobacco and drinks alcohol only in moderation.

"She possesses the physical and mental resiliency required to successfully execute the duties of the Presidency, to include those as Chief Executive, Head of State and Commander in Chief," the doctor wrote.

Harris, 59, is running against Republican Trump, 78, for the White House. She made her medical information public on Saturday in an effort to draw attention to his refusal to do so, according to a Harris aide.

The Harris campaign is eager to highlight the former president's age since he became the oldest candidate in the race after President Joe Biden, 81, stepped aside as the Democratic standard bearer following a poor debate performance against Trump.

Locked in a very tight race. Harris' campaign hopes that contrasting her comparative youth and mental acuity with Trump's more advanced age and tendency to meander, along with the differences in transparency between the two, will help convince undecided voters that she is more fit for office than he.

A White House doctor said in 2018 when Trump was in office that he was in overall excellent health then but needed to shed weight and start a daily exercise routine.

Simmons said Harris's allergies had been well-managed with over-the-counter and prescription medications.

Her urticaria or hives were "sporadic and transient and do not seem to be triggered by any particular exposure nor are they associated with other symptoms" and respond well to antihistamine treatment.

Harris has been on allergen immunotherapy for the last three years, dramatically improving her allergy and urticaria symptoms and negating her need for medication other than occasional nasal spray, he said.

Harris wears contact lenses. Her family history includes her mother's colon cancer. Harris was up to date on preventative health procedures including colonoscopy and annual mammograms, he said. (Reuters)