A new study finds teens who often use e-cigarettes are more likely to become regular smokers and to smoke many cigarettes a day. The study included 3,084 Los Angeles teens who participated in surveys in the fall and spring of tenth grade, Reuters reports. They were asked whether they had tried e-cigarettes, and if so, how often. They were also asked about regular cigarette use. The researchers found more frequent vaping was associated with smoking two or more cigarettes on the days teens chose to smoke. The findings are published in the Journal of the American Medical Association .