Do electronic cigarettes cause less harm than smoking, and will they help me quit?
These are the key questions that people who smoke but wish to quit raise with their healthcare professionals.
They are also hot topics in the ongoing debate about the potential benefits and harms of e-cigarettes and their regulation.
The authors of the new review, who work at Aberdeen Royal Infirmary in the United Kingdom, say that their aim is to inform this discussion.
The Journal of the Royal College of Physicians of Edinburgh has now published a paper on their findings.
"Fewer people," says corresponding study author Abhi Mathur, of the Department of Respiratory Medicine, "are smoking conventional tobacco cigarettes and more people are vaping."
E-cigarettes are battery-operated devices that people use to inhale, or vape, substances — one of which is nicotine. There are several types across hundreds of brands, and the market is growing.
Conventional cigarettes also deliver nicotine into the lungs through inhalation of tobacco smoke. However, they also deliver toxins such as tar and carbon monoxide deep inside the lungs.
Vaping does introduce some of the harmful substances that accompany cigarette smoke into the body, but research suggests that the levels present in e-cigarettes are much lower.
Figures from the World Health Organization (WHO) confirm that the number of people worldwide who smoke tobacco is falling.
However, while the trend may be in decline, large numbers of people continue to smoke, and the impact on public health is still huge.
In 2015, more than 1.1 billion people smoked tobacco products, and the habit "remains the leading preventable cause of illness and premature death," note the review authors.
Against this backdrop, the trend in use of e-cigarettes, or vaping, is on the rise, with millions of people using a range of products.
In the United States, the Centers for Disease Control and Prevention (CDC) estimate that 6.9 million adults, or 2.8 percent of all adults, were using e-cigarettes in 2017. This was the same year in which use of conventional cigarettes fell to its lowest level.
In the U.K., about 6 percent of the population, or 2.9 million adults, used e-cigarettes in 2017. The vast majority of people who use e-cigarettes in the U.K. either smoke or used to smoke, with the latter now outstripping the former.
The rate of e-cigarette use among people who currently smoke in the U.K. stopped rising by 2017, while that among people who used to smoke continued to rise.
In that year, 52 percent of vapers used to smoke, compared with 45 percent who were using both e-cigarettes and conventional tobacco cigarettes.
Only 3 percent of e-cigarette users have never smoked, note the authors. An independent review by an English public health body concluded that while people who have never smoked appear to be trying e-cigarettes, it was unlikely that e-cigarettes were "undermining the long-term decline in cigarette smoking" among young people in the U.K.