There are few more reliable routes to an early grave than cigarette smoking. As a matter of fact, some tobacco users are informed only about how tobacco use can affect people's respiratory system, but not about the fact that over 4,000 kinds of chemicals can be found in tobacco smoke. They are warned of the epidemic being carcinogenic, but not of the fact that at least 40 kinds of cancer-causing substances are lurking in the smoke. They know tobacco use is harmful, but they do not know that tobacco smoke is highly toxic with many pathogenic substances in it, including nicotine, nitrogen dioxide and lead. Tobacco smoke proves more dangerous than industrial air pollution, taking a varied toll on people's brain, heart, lung, liver, stomach and kidney, triggering sexual and procreative dysfunctions, and even leading to birth defects. But despite the dangers, nicotine addicts find it almost impossible to kick the habit. Half of those who try will fail within a week. Fewer than 5% manage to stay clean for a year or more. Crutches such as nicotine patches or gum, which provide the drug without the cigarettes, can help—but only a little.
    One reason is that addiction is about more than mere chemistry. The rituals involved, such as holding a cigarette between the fingers or taking a long, luxuriant puff, can be as habit-forming as nicotine itself. So a better way to stop smoking might be a drug-delivery system that mimicked an ordinary cigarette as closely as possible, but had none of the pesky carcinogens and other poisons which come from burning a rolled-up mix of paper tobacco leaves and additives.
    Electronic cigarettes would seem to fit that bill. They use a small electric heater to vaporize a mix of glycerin and propylene glycol (two fairly inoffensive chemicals) in which nicotine has been dissolved, turning it into a breathable mist that can be savored much as cigarette smoke is. And because some of these devices are designed to resemble traditional cigarettes, they can be held between the fingers and jabbed in the air for emphasis, just like the real thing.
    However, the novelty of e-cigarettes (the first of which hit market in 2006) means there is only a smattering of evidence addressing the question of whether they actually do help smokers ditch the real thing. On December 17th, though, more evidence arrived—in the form of a review published by the Cochrane Collaboration, an international medical research organization. The review's authors, led by Peter Hajck of Queen Mary, a college of the University of London, examined results from 13 trials of e- cigarettes. The results, though a long way from being definitive, are encouraging.
    Two of the studies the team looked at were randomized control trials. These are the highest form of medical evidence, in which doctors assign volunteers at random to the treatment being studied or to something else, and compare the results. In the cases examined, the something else was a placebo e-cigarette. This resembled the real thing, but delivered no nicotine. About 9% of people using electronic cigarettes in these studies managed to abstain from smoking for six months, as against 4% of those using the placebos. One of the studies also found that e-cigarettes were at least as useful as nicotine patches in encouraging abstinence (the other did not examine this question.)
    Giving up smoking is the ideal outcome, but puffing less is good for you as well. Both studies suggested that e-cigarettes help those who cannot face giving up completely to cut their consumption significantly. Some 27% of smokers using placebo e-cigarettes, and 36% of those using the genuine electronic article, were able to do so by half or more. One of the trials also compared e-cigarettes with nicotine patches. In that study, 61% of e-cigarette users were able to cut their consumption by half, compared with only 44% of those using patches. These general conclusions were supported by the 11 remaining investigations, known as cohort studies, in which doctors merely monitored people for a time, without attempting to influence their behavior.  Which of the following does "taking a varied toll on" in the first paragraph mean?