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CHD and stroke risk seriously elevated with just one daily cigarette

No safe level of smoking exists for cardiovascular disease – smokers should quit, not cut down

Louise Prime

Thursday, 25 January 2018

Smoking just one cigarette a day raises the risk of coronary heart disease (CHD) and stroke by about half as much as smoking a pack of 20 a day, UK research has revealed. The authors of the evidence review*, published today in the BMJ, have warned that smokers should be encouraged to quit rather than just cut down if they want to significantly cut their risk of cardiovascular disease. This message is backed up by a public health expert, who also warned of the potential cardiovascular risk posed by ‘heat-not-burn’ cigarettes.

A research team led from University College London and supported by Cancer Research UK conducted a systematic review and metanalysis of 141 cohort studies looking at relative risk of CHD or stroke in men and women smoking one, five or 20 cigarettes a day compared with never-smokers.

They then calculated the excess relative risk for smoking one cigarette per day (RR1 per day−1) expressed as a proportion of that for smoking 20 cigarettes per day (RR20 per day−1). Logically, they pointed out, this figure should be 5%, assuming a linear relation between risk and consumption (as seen with lung cancer); however, this was far from the case.

They reported that for men, smoking just one cigarette a day conferred 46% of the excess risk of CHD risk, and 41% of the excess risk of stroke, of smoking 20 cigarettes a day. For women, the figures were 31% for CHD and 34% for stroke. They also calculated, using only data from studies that controlled for several important potential confounders, a woman smoking just one cigarette a day had about double the CHD risk of a non-smoker.

The study authors concluded: “Smoking only about one cigarette per day carries a risk of developing coronary heart disease and stroke much greater than expected: around half that for people who smoke 20 per day. No safe level of smoking exists for cardiovascular disease. Smokers should aim to quit instead of cutting down to significantly reduce their risk of these two common major disorders.”

The author of an accompanying editorial** pointed out that this study dispels any assumption that smoking less protects against heart disease or stroke. He also argued that new tobacco products, such as e-cigarettes and heat-not-burn cigarettes, might carry substantial risk for heart disease and stroke. He said although e-cigarettes deliver reduced levels of carcinogens, they still expose users to high levels of ultrafine particles and other toxins that might markedly increase cardiovascular risk.

He insisted: “The take-home message for smokers is that any exposure to cigarette smoke is too much. The message for regulators dealing with newly marketed ‘reduced risk’ products is that any suggestion of seriously reduced CHD and stroke from using these products is premature.”

*Hackshaw A, Morris JK, Boniface S, et al. Low cigarette consumption and risk of coronary heart disease and stroke: meta-analysis of 141 cohort studies in 55 study reports. BMJ 2018; 360: j3984 doi: 10.1136/bmj.j3984
**Johnson KC. Editorial: Just one cigarette a day seriously elevates cardiovascular risk. BMJ 2018; 360: k167 doi: 10.1136/bmj.k167

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