John Glenn, who made history twice as the first American to orbit the Earth and the first senior citizen to venture into space, has been hospitalized, a spokesman at the Ohio State University college bearing his name said Wednesday.

No details were offered on Glenn's illness or condition, but spokesman Hank Wilson of the John Glenn College of Public Affairs told AFP that the former astronaut had been admitted more than a week ago to the university's James Cancer Hospital.

"I caution that even though Sen. Glenn is at The James that does not necessarily mean he has cancer," Wilson said.

A hospital spokeswoman contradicted Wilson's account, saying Glenn was not listed in the cancer hospital's patient directory.  

Glenn is 95 years old and has been in declining health, undergoing heart-valve replacement surgery in 2014 and suffering a stroke, according to the Cleveland Plain Dealer which broke the story of his hospitalization. 

The former astronaut served as a Democratic senator from Ohio for 24 years after his 23-year career in the US military and space program.  

In 1962 he was the first US astronaut to orbit the Earth in a flight lasting just under five hours, and returned to space decades later at the age of 77 -- becoming the oldest astronaut in space.  

Barack Obama awarded Glenn the Presidential Medal of Freedom in 2012, the country's highest civilian honor.

"On the morning that John Glenn blasted off into space, America stood still," Obama said during the medal ceremony. 

"The first American to orbit the Earth, John Glenn became a hero in every sense of the word," the president said. 

Glenn served in both World War II and the Korean War, and in 1957 he made the first nonstop supersonic flight from Los Angeles to New York.