"I don't know what I was doing, but I used to have the odd cigarette, sitting on my own. I was worried that I'd smell of cigarettes so I started brushing my teeth.
"I decided then that if I could get anything out of the tour I might have white teeth."
O'Connell also backed England's controversial and heavily suspended hooker Dylan Hartley to captain the British and Irish Lions in New Zealand next year.
"He seems to have learned from all of the scrapes he's been in," said O'Connell.
"I think he'd be a great captain."
O'Connell has also spoken out about player burnout, and the scheduling of next year's British and Irish Lions tour to New Zealand, suggesting the touring side have a minimal chance of succeeding given the time between the end of the European domestic season and the Lions' first tour match in New Zealand.
O'Connell, who played in 108 tests for Ireland and seven for the Lions, said in a recent interview with the Daily Telegraph that anyone who has to play more than 25 matches in a single season is putting themselves at risk of injury.
"I don't think the body can sustain more than 24, 25 matches a season," O'Connell told the Telegraph's chief sports writer Paul Hayward.
"If you're asked to play any more than that, you're putting your body at risk."
"I think they can [manage it], but they'll probably pay a price next season," he said of the schedule the Lions face in their upcoming tour of New Zealand in June-July next year.
"The Six Nations will pay a price next season, club owners will pay a price. Guys will be worn out and injured. To me as a player, the Lions was the ultimate. I loved it. And I just think it should be looked after a little better in the calendar.
"I think they're playing their first game six days after the end of the domestic season. I'm tempted to say - what chance do they have? What chance do they have to spend a bit of time together to become a team, which is really, really important.
"We probably didn't invest a lot in that in 2005. In 2009 when Gats [Warren Gatland] and Geech [Ian McGeechan] were there, we really did that. The same under Gats in 2013. It's an important part of the Lions having a chance to win games."
O'Connell's comments come shortly after worldwide talk throughout the rugby community of the possibility of a 'global season' being turned into reality as a way of easing travelling and playing demands on the world's top players.
The 36-year-old felt the full effect of of player burnout in a cruel manner during last year's Rugby World Cup.
Playing in his final tournament as an Ireland international, O'Connell was the victim of a hamstring injury in their final pool match against France in Cardiff.
The injury ruled him out for the remainder of the tournament, meaning he went on to miss Ireland's quarter final against Argentina, a match where O'Connell's experience and passion could have prevented a loss for the Irish.
The first match of the Lions tour next year is against a Provincial Union XV in Whangarei on 3 June, quickly followed by matches against the Blues on 7 June and the Crusaders on 10 June.
The final of England's Aviva Premiership takes place on 28 May (UK time), while the final of the Pro12, the competition that the Scottish, Irish, Welsh and Italian clubs compete in, takes place in Edinburgh a day earlier.
As a result, players slected for the Lions particpating in those finals have just a week to overcome their euphoria/disappointment - depending on the result - and travel to New Zealand to prepare themselves for the tour.
Players in contention for the British and Irish plying their trade for clubs in France's Top 14 competition, such as Leigh Halfpenny of Wales, may miss out altogether, with their domestic season running through to mid-June, although exact dates of their play-off matches this season are yet to be decided.
