Democratic presidential candidate Kamala Harris has released her medical report in a challenge to older and secretive Donald Trump, 78, to do the same.

The Harris campaign is eager to highlight Trump’s age since he became the oldest candidate in the race after President Joe Biden, 81, stepped aside.

In a letter released on Sunday (AEDT), a US military doctor gave Harris a clean bill of health and said she “possesses the physical and mental resiliency” required to serve as president.

Dr Joshua Simmons, a US Army colonel and physician, wrote that Harris, 59, maintained a healthy, active lifestyle and that her most recent physical last April was “unremarkable”.

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,” he wrote in a two-page letter.

Simmons, who said he has been Harris’ primary care physician for the past 3.5 years, said the vice president has a history of allergies and urticaria, also known as hives, for which she has been on allergen immunotherapy for the past three years.

Simmons said Harris’ latest blood work and other test results were “unremarkable.”

Also in the report:

• Harris wears contact lenses for mild nearsightedness
• Her family history includes maternal colon cancer
• She is up to date on preventive care recommendations, including having a colonoscopy and annual mammograms.

Harris’ advisers hope to use the moment to draw a contrast with Trump, who has released only limited information about his health over the years.

They hope to raise questions about his fitness to serve, according to a campaign aide.

Trump has released very little health information, including after his ear was grazed by a bullet during an assassination attempt in July.

Trump refused to release his medical records during his first presidential campaign in 2016.

Most details known about his health are from a physician’s report nearly seven years ago which revealed he was overweight, had high cholesterol and suffered from rosacea, a skin condition that causes face redness.

Trump eagerly questioned President Joe Biden’s health when the 81-year-old president was seeking re-election.

Since Biden was replaced on the ticket with Harris, who is 59, Trump’s own health has drawn more attention.

-with AAP