No safe level of smoking exists, say epidemiologists who have shown that just one cigarette a day raises an individual’s cardiovascular half as much as a person who smokes a pack a day.

A review of the evidence by UK researchers found that the cardiovascular risk with low levels of smoking was much higher than previously thought.

Men who smoked one cigarette per day had 46% of the excess risk of heart disease and 41% of the excess risk of stroke associated with smoking 20 cigarettes per day, much higher than the expected 5% excess risk.

Published in the BMJ, the findings are another strong reminder of the importance for smokers to quit completely rather than cutting down to reduce their risk of heart disease and stroke.

The new information might be particularly helpful at the start of a new year, when many smokers are likely to be thinking about stopping or smoking less, the researchers from University College London suggest.

“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,” they write.

“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.”

Smokers may also need reminding that cardiovascular disease, not cancer, is the greatest mortality risk for smoking, causing about 48% of smoking-related premature deaths, they add.

“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,” they conclude

An accompanying editorial says the findings also have a message for tobacco regulators when it came to dealing with newly marketed ‘reduced risk’ products

“Any suggestion of seriously reduced coronary heart disease and stroke from using these products is premature,” it warns.

The review analysed the results of 141 studies and estimated the relative risks for smoking one, five, or 20 cigarettes per day. It also found that  for women, those who smoked one cigarette per day had 31% of the excess risk of heart disease and 34% of the excess risk of stroke associated with smoking 20 cigarettes per day. Women’s heart disease risk was more than doubled with one cigarette per day, when only studies that controlled for several factors were included in the analysis.