He explained: "I have had a scan so I know what it is; it's a protruding disc. I could have had an injection last week but thought I would wait, give it a little bit of time. So we will see if it clears up a bit."
He said his doctor had made clear it was not a slipped disc and that the prime ministerial body was in "good nick" but Mr Cameron noted: "He said when you get into your mid-40s, this starts to happen."
Mr Cameron spoke of his love of Jura, where his wife Samantha's stepfather Viscount Astor owns a 20,000-acre estate, saying the island was "really special" and was a great place to unwind. He added: "I like the great outdoors. I like an active holiday."
He said he enjoyed walking and fishing and also liked to go horse riding but "not bare-chested" like Russian Premier Vladimir Putin.