TIM PALMER: A large scale Australian study has revealed the risk of dying from light, casual smoking is much higher than previously though.
The study, which looked at the health records of 200,000 Australians, found even 10 cigarettes a day doubles fatal risks compared to people who don't smoke.
It concludes that two-thirds of smokers' deaths are linked to their smoking, much higher than the previous estimate of about one in two.
Will Ockenden spoke to the Sax Institute's professor Emily Banks.
EMILY BANKS: What we did was we followed 200,000 members of the 45 and Up study over time for around four years and what we found was that the people who were current smokers had around three times the risk of dying during that period than people who had never smoked.
And we also found that increased risk of death varied according to how much people smoked. And among the people who were light smokers, or who would consider themselves light smokers, smoking an average of around 10 cigarettes a day, they still had around double the risk of death compared to someone who had never smoked.
It's quite interesting to think that the risk related to smoking an average of 10 cigarettes a day in terms of your risk of death is very similar to the risk of being morbidly obese, so if you have a body mass index of 35 or more. And I think most people who smoke wouldn't really think of themselves as having a similar level of risk.
WILL OCKENDEN: It's not news to say that smoking is dangerous, we've known this for a long time. And indeed there have also been studies about light smoking in the past as well. What does your study show that is new?
EMILY BANKS: Well, the thing is that we've relied on international evidence to really quantify the risks relating to smoking and each population has a different pattern of smoking. And what we see in Australia is because people have been smoking intensely for long periods of time, we have what's called a mature epidemic and what we need to quantify that is really local data. So what we're actually seeing now is we have local data.
And we're also seeing that the risks are really higher than has been sort of proposed internationally. The risk of death in that follow-up period is around three times, in current smokers its around three times that in never smokers.
That's really meaning that around two-thirds of smokers will actually die of smoking related problems. So what's been bandied internationally is around 50 per cent, you know, that smoking is like tossing a coin, heads you die and tails you spend a lot of money on smoking, but really what we're seeing is it's more like two-thirds.
WILL OCKENDEN: Why did you look at light smoking?
EMILY BANKS: Well, we really wanted to look at what we call a dose response. So we wanted to look at how much the risk of death varies according to the amount you smoke. So we didn't deliberately just focus on light smoking. What we did was look at the risk according to the number of cigarettes that people smoke.
And what we found was there was a very clear continuum. There is no threshold; so there's no sort of safe amount of smoking. And it's actually a reasonably steep curve so with that average of 10 cigarettes a day you're a bit over a relative risk of two, which means a doubling in risk. But as you get towards people smoking 25 cigarettes or more, you're talking about a four-fold or a five-fold increase in risk.
WILL OCKENDEN: What happens if you're only smoking one or two on the weekend at a party?
EMILY BANKS: Well, we really can't measure the effect of that because it's really too low but the assumption is it's going to be somewhere on that continuum. It' not going to be nothing, but it's not going to be as substantial as if you're smoking 10 cigarettes a day or more.
TIM PALMER: Professor Emily Banks from the Sax Institute talking to Will Ockenden.