A review of evidence published in the British Medical Journal (BMJ) concludes that no safe level of smoking exists and smokers should aim to quit instead of trying to cut down.
The latest figures show that, in Scotland, tobacco use is associated with over 10,000 deaths and around 128,000 hospital admissions every year.
A team of researchers led by Professor Allan Hackshaw at the UCL Cancer Institute at University College London analysed the results of 141 studies and estimated the relative risks for smoking one, five, or 20 cigarettes per day.
They found that smoking just one cigarette a day has a much higher risk of developing coronary heart disease and stroke than expected - about half the risk of smoking 20 per day.
The researchers say their findings have important consequences for many smokers and health professionals who believe that smoking only a few cigarettes carries little or no harm. They argue that smokers should stop completely instead of cutting down to significantly reduce the risk of heart disease and stroke.
Individual studies have reported that smoking only one to five cigarettes per day is associated with a higher than expected risk of heart disease.
Researchers found that men who smoked one cigarette per day had 46 per cent of the excess risk of heart disease and 41 per cent of the excess risk of stroke associated with smoking 20 cigarettes per day (much higher than the expected 5 per cent).
For women, those who smoked one cigarette per day had 31 per cent of the excess risk of heart disease and 34 per cent 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.
The authors of the report said: “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.
“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. No safe level of smoking exists for cardiovascular disease.”
READ MORE: Campaign to stub out smoking in Scotland
Public Health Minister Aileen Campbell said: “Quitting smoking is the best thing a smoker can do to improve their health. We continue to ensure that the right type of support is in place through our cessation services, including supporting people to select aids to suit their own needs.
“The new Tobacco Strategy, which will be published in 2018, will focus on addressing health inequalities and targeting smoking rates in the communities where people find it most difficult to quit.”
Simon Clark, director of the smokers' group Forest, said: "Quitting smoking can be hard and for many people cutting down is often the first step.
"Discouraging it as an option could be counter-productive because smokers who want to quit or reduce their consumption may be dissuaded from even trying."
He added: "What researchers consistently fail to understand is why many people smoke.
"Millions smoke not because they are addicted but because they enjoy it. For some it's one of their few remaining pleasures, for others it's a comfort.
"Health considerations are obviously a factor in whether or not people smoke but there are other factors, including pleasure, that determine people's choices and no amount of scaremongering about the risks of even a single cigarette a day will change that."