ST. PAUL - It is out with Diet Coke and in with water for Minnesota Gov. Mark Dayton after a short hospitalization blamed on dehydration.

With a smile Tuesday, the 69-year-old governor told reporters: “As Mark Twain said, reports of my demise are greatly exaggerated.”

Dayton, Minnesota’s oldest-ever governor, said doctors told him that he suffered from dehydration when he fainted at a Woodbury political gathering Sunday night. They told the governor “after 24 hours of waiting and waiting and tests that I have a healthy heart.”

He was in Regions Hospital, near the state Capitol, Sunday night through Monday afternoon after he fainted during a political gathering.

The episode taught Dayton that Diet Coke has to go. In its place, he introduced his “new best friend,” a bottle of water. He held up a bottle for the press corps to capture the new buddies.

Dayton said he considers his health to be good.

“I know that I am not 39 years old,” he said. “My mental acuity is very good.”

Dayton said that he had stood for more than two hours at two Sunday night political events, in hot homes, which prompted his back to “stiffen.” He said he was not in pain, but when others suggested he go to the emergency room he agreed just in case he had hit his head when he fell.

Whenever his health is discussed, reporters bring up frequent rumors that he plans to resign before his second term as governor ends in three years. He said he will serve out his term unless he dies.

Dayton has said this will be his last term in public office after also serving as state auditor and U.S. senator.

The governor has had hip and back surgery while in office, and at times has hobbled with a cane.

Mayo Clinic, where the governor has gone for recent health issues, reports that as people age they become more susceptible to dehydration. One reason is that a body can conserve water less as it ages; older people also eat less, which reduces liquid intake.

Dayton said that people his age and older should not hesitate running for office, mentioning the two Democratic presidential candidates. Sen. Bernie Sanders is 74 and Hillary Clinton is a few months younger than Dayton.

“They certainly have shown their ... vitality,” the Democratic governor said.