Pope Francis has revealed his debt to a nun who saved his life by increasing his medication when he suffered from a lung condition at the age of 21

In a new book, I Fioretti di Papa Francesco (The Little Flowers of Pope Francis) by Andrea Tornielli, a veteran Vatican journalist, the pontiff speaks of his gratitude to the nuns who worked in the hospital where he was ill as a young man.

“I am alive thanks to one of them,” Pope Francis said. “When I had lung problems in the hospital, the doctor gave me penicillin and antibiotics in small doses.

“The nun who was on the ward tripled that because she had an intuition, she knew what to do, because she was with the ill all day long,” the pope said.

“The doctor, who was very good, spent his time in a laboratory, but the nun was living on the front line and talking with those on the front line every day.”

Pope Francis’s historic lung illness drew questions when he was in the spotlight after his predecessor Pope Benedict XVI resigned due to his failing health and inability to handle the job.

Francis reportedly had three cysts on his lung before part of it was removed and fresh concerns were raised about the health of the former Cardinal Jorge Mario Bergoglio when the 76-year-old was elected in March this year.

At the time, Father Federico Lombardi, the Vatican spokesman, said: “This is not a handicap in his life. Those who know him have always seen him in good health.” Pope Francis is due to celebrate his 77th birthday next week and the book’s author, Andrea Tornielli, said on Sunday that the pope was currently in very good health.

“His health is good and he shows great stamina,” Mr Tornielli told The Telegraph.

“He works many hours a day and spends many hours a week greeting people in St Peter’s Square in the freezing cold.”

•Excerpted from The Telegraph.