Smoking just one cigarette a day carries half the risk for cardiovascular disease and stroke as a pack-a-day habit, according to research that concludes there is no safe level of smoking.

(Photo: Reuters/Michaela Rehle)

The study team analysed data from 141 smaller studies to assess the risk of heart disease and stroke for people who smoked one, five or 20 cigarettes a day. Men who smoked one cigarette a day were 74 per cent more likely to have heart disease and 30 per cent more likely to have a stroke than men who never smoked at all, they report in The BMJ.

Women who smoked one cigarette daily were more than twice as likely to develop heart disease and 46 per cent more likely to have a stroke than women who didn’t smoke.

“People who have always been light smokers will have a higher risk of cardiovascular disease than many of them expect,” said lead study author Allan Hackshaw of the Cancer Institute at University College London in the UK.

While their risk is still lower than for heavy smokers, the results should offer fresh motivation for light smokers to quit altogether, Hackshaw said by email. Heavy smokers, meanwhile, can benefit from cutting back even if they can’t quit.

“Cutting down is certainly better than smoking the same high amount,” Hackshaw advised. “And cutting down has significant reductions in the risk of cancer and other disorders; hence, it is absolutely important that people try this if they find it too difficult to stop completely.”

For example, men who smoked about a pack a day had more than twice the risk of heart disease as non-smokers, while the risk was 58 per cent higher than non-smokers’ for men who smoked five cigarettes a day, and 48 per cent higher for men who smoked just one.

Similarly, women who smoked five cigarettes daily had 43 per cent of the excess of heart disease associated with a pack-a-day habit, while women who smoked one cigarette a day had 31 per cent of the excess risk.

Compared to non-smokers, men who smoked 20 cigarettes a day were 64 per cent more likely to have a stroke and women had more than twice the risk for stroke.

The study wasn’t a controlled experiment designed to prove whether or how the number of cigarettes people smoke on a typical day might impact their risk of heart disease or stroke.

Another limitation of the analysis is that researchers lacked data on inpidual patient characteristics from many of the smaller studies, making it impossible to assess whether the study results might be explained by factors that can independently lead to stroke and heart disease and stroke such as obesity and diabetes.

Even so, the findings should serve as a reminder that no amount of smoking is safe, said Kenneth Johnson of the School of Epidemiology and Public Health at the University of Ottawa in Canada, who wasn’t involved in the study.

That’s because smoking can lead to an irregular heart beat, blood clots too well, thickening and stiffening of the artery walls and increased blood pressure, Johnson, author of an accompanying editorial, said by email.

“With regard to the number of cigarettes, it’s a little like with matches; you only need one - not the whole box - to start a fire,” Johnson said.

“Even secondhand smoke appears to trigger these damaging processes, resulting in 80 per cent to 90 per cent of the effect associated with active smoking.”

VNF/Reuters