Researchers examined data collected from one-time surveys of 30,272 people aged 20 to 75 years about their smoking habits, e-cigarette use and respiratory symptoms that might indicate breathing diseases like asthma or chronic obstructive pulmonary disorder (COPD). Compared to people who never smoked, current smokers were 18 times more likely to use e-cigarettes, the study found. Ex-smokers were more than twice as likely as people who never smoked to use e-cigarettes.