Just One Cigarette Daily Raises Coronary Disease and Stroke Risks: Meta-analysis

Smoking even one cigarette each day raises the risks of coronary heart disease and stroke, a new meta-analysis suggests. Interestingly, researchers also found that the risks carried by smoking are disproportionate to the number of cigarettes smoked.

Compared with people who’ve never smoked, men and women who say they smoke a single cigarette each day still see a 48% and 57% relative increase in coronary heart disease risk, respectively. For those who smoke 20 cigarettes each day, the risks are 204% and 284% higher than if they’d not taken up smoking. Stroke risks show a similar pattern, investigators led by Allan Hackshaw, PhD (University College London, England), reported this week in the BMJ.

“The thing with cardiovascular disease is that when you cut down to only a couple a day your risk doesn't come down by one-twentieth,” Hackshaw told TCTMD. “If you smoke 20 a day and you cut down to one a day, you'd think your risk would be one-twentieth intuitively. And it's not one-twentieth, it's around 50 percent. It's just huge.”

That said, Hackshaw cautioned, the new findings don’t erase the importance of cutting back in reducing cancer risk.

“For many physicians and other health professionals, their primary goal is to get smokers to quit completely,” he said. “But there are some smokers who just find it really difficult, and it’s not really [their fault] because cigarette smoking is terribly addictive. So an option for them is to cut down, and that seems to work for quite a few smokers.”

When it comes to cancer, he stressed, “it’s much better to cut down to one or five a day rather than staying on 25 or 30 a day. It’s a good approach. . . . But if you want to get rid of your risks of heart attack and stroke, for that you’ve got to stop completely. And that’s the bottom line of [our] paper.”

If you want to get rid of your risks of heart attack and stroke, for that you’ve got to stop completely. Allan Hackshaw

For their new analysis, Hackshaw and colleagues identified 55 publications with a total of 141 cohort studies published between 1946 and 2015. The data set included data on coronary heart disease in 5.6 million individuals and stroke in 7.3 million individuals.

When the researchers separated studies based on whether they did or did not adjust for multiple confounders, the adjusted data showed an even higher increase in risk with smoking versus never smoking. Moreover, the risk posed by one cigarette versus 20 grew even more outsized.

Adjusted RR (95% CI) Compared With Never Smoking

“We show clearly that no safe level of smoking exists for cardiovascular disease at which light smokers can assume that continuing to smoke does not lead to harm,” the investigators conclude.

To TCTMD, Hackshaw explained why the risks of heart disease and stroke don’t decrease proportionally in relation to the number of cigarettes smoked. “With cancer, the bad health effects take several years to come through, whereas with cardiovascular disease it only takes a couple of years for the bad things to happen,” he said. “That’s why you get these big increases in risk when you’re only smoking a couple [of cigarettes] a day.”

The good news, Hackshaw added, is that “because your risk of these two things comes on quickly, the risk also goes [away] very quickly. . . . It only takes a few years for it to go away almost completely. That’s a positive thing to try and take forward.”

Cutting Back vs Quitting

In an accompanying editorial, Kenneth C. Johnson, MD (University of Ottawa, Canada), points out that although the current results are “compelling,” this is not the first hint that “low” exposure to tobacco smoke carries cardiovascular risk. Further, the association makes sense, he writes: “A highly nonlinear relation exists between exposures to fine particulate matter (PM2.5) from cigarette smoke and ambient air pollution and their adverse effects on the cardiovascular and pulmonary systems, including systemic oxidative stress, inflammatory vascular dysfunction, increased platelet activation and blood viscosity, atherosclerosis, ischemic heart disease, and altered cardiac autonomic function.”

Johnson stresses that individuals must quit smoking to eliminate their added cardiovascular risk. “Only complete cessation is protective and should be emphasized by all prevention measures and policies,” he says.

What makes him especially wary is the possibility that people may turn to newer alternatives, like e-cigarettes and heat-not-burn tobacco products.

“Although e-cigarettes deliver reduced levels of carcinogens, they still expose users to high levels of ultrafine particles and other toxins that may markedly increase cardiovascular risk. Somewhat lower emissions of many toxic substances from heat-not-burn cigarettes do not make these products safe,” Johnson observes. “Regulatory approval of these products should be withheld. We cannot afford to wait several more decades to document the illness, disability, and deaths caused by new recreational tobacco and nicotine products.”

Furthermore, he adds, the data by Hackshaw et al discourage the use of such products as a means of “harm reduction,” since cutting back on cigarettes does not proportionally decrease the potential for harm.

Hackshaw, however, is not yet convinced that e-cigarettes and other such products aren’t sometimes helpful, even if possibly risks are not yet fully known. For “people who’ve been smoking for quite some time,” he said, “it’s much better to switch [to a cigarette alternative] rather than sticking to your 20 a day or even three to five a day.”

Never smokers can “have a tendency to underestimate how difficult it is to quit. So, if that’s the case, you cut down and help cut out, and do whatever [mix] suits you,” Hackshaw said.