Democratic presidential candidate Sen. Elizabeth Warren (D-MA) speaks to guests during a campaign stop at the Val Air Ballroom on November 25, 2019 in West Des Moines, Iowa.

Sen. Elizabeth Warren released a doctor's note on Friday saying the 70-year-old candidate is in good health, as voters consider the vitality of her and her fellow septuagenarians vying for the Democratic nomination.

"Senator Warren is in excellent health and has been throughout the 20 years I have served as her physician," Dr. Beverly Woo of Boston's Brigham and Women's Hospital said in a letter dated Wednesday, according to NBC News.

Woo wrote that there are "no medical conditions or health problems that would keep her from fulfilling the duties of the President of the United States."

The memo noted that Warren has never smoked, used drugs or had a problem with alcohol, and that she exercises regularly and eats healthy foods. Her only medical condition, hypothyroidism, is being treated by a daily dose of levothyroxine. Blood tests in January, taken at her most recent physical, came back normal.

The clean bill of health comes as voters consider whether the race's oldest contenders are up to the grueling task of running the country.

A survey conducted for the Los Angeles Times and released Thursday found that a third of voters are concerned that Sen. Bernie Sanders and former Vice President Joe Biden could be hampered in the job because of their ages.

Sanders, 78, and Biden, 77, lead Warren in support in national surveys. But voters are less concerned about Warren's health.

Only 7% in the poll had concerns about her age. Warren has made a show of her endurance during the race, frequently spending hours on her feet after campaign events taking photos and chatting with supporters.

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Michael Bloomberg, the former mayor of New York who entered the primary contest last month, is 77. The poll said 17% of voters are concerned about his age.

Sanders and Biden did not immediately respond to requests for comment. A Bloomberg aide said the billionaire will release his medical records.

Biden has said he will release his medical records before votes are cast, and has criticized those who have questioned his vigor, challenging one Iowa voter to pushup and IQ contests on Thursday.

Sanders, who was hospitalized in October after a heart attack, has said he will release his medical records by year's end. Sanders made public a doctor's note during his 2016 run that pronounced him to be in good shape.

President Donald Trump, who is 73, has had numerous physicals while in office. In February, his physician said that Trump was in "very good health."

In November, the president made an unannounced visit to Walter Reed National Military Medical Center that the White House said was the first part of his routine annual physical.

The White House did not release details about the visit, but press secretary Stephanie Grisham said following the examination that Trump was healthy, "as demonstrated by his repeated vigorous rally performances in front of thousands of Americans several times a week."