Researchers compared the effects of smoking a single cigarette to smoking 20 a day and found there wasn’t a huge difference in the effects. In fact, smoking one a day only halved the risk of heart disease when compared to smoking 20.
Researchers said their findings have important consequences for many smokers and health professionals who believe that smoking just a few cigarettes carries little or no harm.
They warned smokers to stop smoking completely instead of cutting down.
Individual studies have reported that smoking only one to five cigarettes per day is associated with a higher than expected risk of heart disease.
To investigate this further, a team of researchers led by Professor Allan Hackshaw at the Cancer Institute at University College London analysed the results of 141 studies and estimated the relative risks for smoking one, five, or 20 cigarettes per day.
If the risk for smoking 20 cigarettes per day is 100%, the expected risk for smoking one a day is around 5%. However for both genders, the actual risk turned out to be much higher:
:: Men who smoked one cigarette per day had 46% of the risk of heart disease associated with smoking 20 cigarettes per day.
:: Men who smoked one cigarette per day had 41% of the risk of stroke associated with smoking 20 cigarettes per day.
:: Women who smoked one cigarette per day had 31% of the risk of heart disease associated with smoking 20 cigarettes per day.
::Women who smoked one cigarette per day had 34% of the risk of stroke associated with smoking 20 cigarettes per day.
:: Women’s heart disease risk was more than doubled with one cigarette per day.
The study’s authors wrote in the BMJ: “We have shown that a large proportion of the risk of coronary heart disease and stroke comes from smoking only a couple of cigarettes each day. This probably comes as a surprise to many people. But there are also biological mechanisms that help explain the unexpectedly high risk associated with a low level of smoking.”
They acknowledged some study limitations, but said their paper is the first to combine results across many studies covering both coronary heart disease and stroke.
They hailed the findings as “a valuable reference that can be used to strengthen public health campaigns, and provide a strong health incentive for smokers to stop completely (particularly women)”.
Cardiovascular disease, not cancer, is the greatest mortality risk for smoking, causing about 48% of smoking-related premature deaths.
The authors concluded: “No safe level of smoking exists for cardiovascular disease. Smokers should quit instead of cutting down, using appropriate cessation aids if needed, to significantly reduce their risk of these two common major disorders.”
In a linked editorial, Kenneth Johnson, Adjunct Professor at the University of Ottawa, outlined the major public health implications of these results, and said “only complete cessation [quitting] is protective and should be emphasised by all prevention measures and policies”.
The take home message for smokers is that “any exposure to cigarette smoke is too much,” he added. “The message for regulators dealing with newly marketed ‘reduced risk’ products is that any suggestion of seriously reduced coronary heart disease and stroke from using these products is premature.”
Deborah Arnott, chief executive of health charity ASH, said: “Many smokers think that they’re not at risk if they only smoke one or two a day. This research shows that’s just not true, particularly when it comes to heart disease and stroke.
“If you can’t quit, get help. Smokers are up to four times as likely to succeed if they get help from their local stop smoking service or GP than if they try to quit unaided.”