Just one cigarette a day is enough to raise the risk of heart disease and stroke by around 50 per cent.
Researchers have found those who smoke once a day expose themselves to fully half the risk of heart disease and stroke seen in people who smoke 20 cigarettes.
Men who smoked one cigarette a day had 46 per cent of the increased risk of heart disease seen in people who smoked 20. Their danger of a stroke was 41 per cent of that seen in 20-a-day smokers.
Just one cigarette raised their risk of coronary heart disease by 48 per cent compared to being a non-smoker.
Women meanwhile saw their heart disease risk more than double with one cigarette a day, compared to if they did not smoke at all.
Researchers at UCL have found those who smoke once a day expose themselves to fully half the risk of heart disease and stroke seen in people who smoke 20 cigarettes
The review of more than 140 scientific studies was led by Professor Allan Hacksaw from the UCL Cancer Institute at University College London, and states: ‘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.’
As smoking has fallen out of fashion in Britain, a quarter of people report only having one to five cigarettes a day.
Those who smoke just once every 24 hours may assume their risk of health problems is minimal. That is certainly the case for lung cancer, where one cigarette has approximately five per cent of the risk of smoking 20 of them.
But the review found cutting down significantly has little effect on the risk of heart disease or stroke, which appears to be higher for women than men.
Among 100 people who smoke 20 cigarettes a day, approximately an extra seven people will suffer a heart attack or stroke because of the habit. And for 100 who smoke one cigarette a day, an extra three will have a heart attack or stroke.
The results, published by the BMJ, show women who smoked one cigarette per day had almost a third of the extra risk of heart disease and stroke associated with smoking 20 cigarettes per day.
Women’s heart disease risk was more than doubled with one cigarette per day, according to one analysis in the research.
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.
This 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 research team looked at the risks from smoking one, five, or 20 cigarettes per day inn a trawl of studies from 1946 to 2015.
‘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,’ the authors conclude.
‘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.’
In a linked editorial, Kenneth Johnson, Adjunct Professor at the University of Ottawa, states: ‘The high cardiovascular risk associated with very low cigarette use has major public health implications.
‘Firstly, light smoking, occasional smoking, and smoking fewer cigarettes all carry substantial risk of cardiovascular disease. Only complete cessation is protective and should be emphasised by all prevention measures and policies.’