Perhaps you’re a smoker, and perhaps you’ve been dragging your feet about quitting. Perhaps the hollow willpower of a New Year’s resolution is not motivation enough? Conveniently for you, new research has been published in the British Medical Journal that may encourage you to cut down. Way down. To zero.
Statisticians supported by Cancer Research UK have concluded that smoking just one cigarette a day still carries half the risk of developing coronary heart disease or having a stroke that’s associated with smoking 20 per day.
This warning was drawn from reviewing nearly 60 years’ worth of medical studies.
“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,” say the authors. “This probably comes as a surprise to many people.
The group was interested in determining the health risks posed by light smoking after encountering evidence that a growing number of cigarette consumers actively try to decrease how much they smoke, but are not looking to stop altogether. The authors attribute this unconcerned attitude to the assumption shared by many light smokers (up to 35 percent in the US) that having five or fewer cigarettes a day is not very harmful to one’s health.
Prior research has shown that the risk of developing lung cancer is more or less linear: The risk of disease goes up proportionately as the number of cigarettes consumed goes up. Yet existing evidence on smoking and cardiovascular disease (coronary heart disease and stroke combined) suggests that this relationship is more logarithmic – risk jumps up significantly following any amount of smoking and then levels off. Despite the availability of this information, the authors note that most of the general public and even medical professionals appear unaware of the dangers of light smoking.
To further substantiate – and consequently widely share – such findings, the group analyzed results from 141 prospective studies that followed the health outcomes of smokers of varying levels (plus control groups of nonsmokers) over long periods of time.
The outcome of interest was the difference in “excess relative risk” between a multiyear habit of smoking one cigarette a day and smoking a standard pack. Essentially, if smoking 20 confers a 127 percent increased likelihood of heart disease, what percentage of that risk are you maintaining by only having one?
After performing multiple calculations that accounted for age and other influencing factors (such as blood pressure and history of diabetes), they discovered that the difference in risk for coronary heart disease was 53 percent in men and 38 percent in women. For stroke, the change in excess risk was 64 percent and 36 percent for men and women, respectively.
If smoking’s effect on these grave conditions was truly linear, as is so much more comforting to believe, the difference in risk would have been only 5 percent.
“No safe level of smoking exists for cardiovascular disease,” emphasize the authors. “Smokers should aim to quit instead of cutting down to significantly reduce their risk of these two common major disorders.”
One major limitation of this study was the generalizations made about participants’ cigarette consumption. Daily cigarette counts were put into quantity brackets (e.g. 1-5, 6-10) that may have been inconsistent across studies and, in a best-case-scenario, are an estimate for a fluctuating habit. Additionally, a notable margin of error is always present in reviews that include studies with differing methodologies.
These issues aside, the incredibly thorough paper serves as a useful reference for medical professions and a strong incentive for waffling smokers. But please don’t use this as an excuse to give in and start smoking a full pack.