LONDON — For people who think that smoking only one or two cigarettes a day carries little cardiovascular risk, a powerful new study maintains the only way to reduce risk is to quit, full stop.
The investigators anticipated that smoking one cigarette a day would be associated with about 5% of the excess relative risk of smoking 20 cigarettes a day, but they found it actually accounts for 46% of excess CHD risk in men and 31% of the risk in women.
For the less commonly reported smoking-related outcome of stroke, the excess risk associated with just one cigarette per day was 41% for men and 34% for women.
The meta-analysis of data from 141 prospective cohort studies was published online today in the British Medical Journal.
“There’s been a big shift from people smoking 20 to 25 cigarettes a day to only smoking a few cigarettes a day with the assumption that’s good enough for them. Their view is that smoking only a couple a day can’t be harmful and that’s probably not far off the truth for risk for cancer. For many smokers that’s probably the first thing that comes to mind, but cardiovascular risk is the big one,” lead author, Dr Allan Hackshaw (University College London, UK), told theheart.org | Medscape Cardiology.
He continued, “So the main public health impact of this is that smokers have done well in reducing and there are various methods to help them quit and cut down, but the aim is to keep on searching for those methods, find one that suits them, and to cut down and then quit completely.”
Dr Vincent Bufalino (Advocate Health Care, Chicago, IL), who was not involved in the study, said the findings are not what many physicians would have predicted but that the investigators have built a “very convincing case” in a pretty impressive set of data.
“I think this is actually stunning in that it’s an all-or-nothing phenomenon now,” he said. “It’s going to change our thinking. Of course we wanted people to quit. It’s not like we were trying to encourage people to reduce; we would take that only as the third option if everything else failed. But now we have some hard data that says even a cigarette a day is harmful—and not just a little harmful, but increases your risk 50% to 75% of the time. Wow! And it’s even more impressive in women.”
The excess CVD risk associated with low smoking has been reported since the 1990s and is likely known by expert cardiologists, especially those familiar with tobacco research, but “in terms of a lot of the everyday practicing cardiologists, I have the feeling that they don’t,” Hackshaw said.
“It could be possibly that when those occasional reports have come out in journals and in the media, they’re only based on one study—people say it’s only one study, it might be a fluke and that’s why it hasn’t sunk in properly,” he added.
Women, Be Wary
The 141 cohort studies in the meta-analysis were published between 1946 and May 2015 and followed 5.6 million patients for CHD and 7.3 million for stroke. Each study had at least 50 hard events, with 110,000 new cases of CHD and 135,000 cases of stroke reported.