An analysis of federal data by University of Iowa researchers published in JAMA finds that more American adults have tried e-cigarettes, but the rate of current use appears to be declining.

Wei Bao, assistant professor of epidemiology in the UI College of Public Health, analyzed national data from more than 101,000 Americans who participated in the annual National Health Interview Survey (NHIS) by the US Centers for Disease Control and Prevention (CDC). The NHIS has asked adult participants since 2014 whether they currently use e-cigarettes every day, some days, or not at all.

Bao’s analysis found that the number of adults who tried e-cigarettes increased—from 12.6% in 2014 to 13.9% in 2015 to 15.3% in 2016. However, during the same time, the survey showed that the number of people who said they currently use e-cigarettes “every day” or “some days” decreased—from 3.7% in 2014 to 3.5% in 2015 to 3.2% in 2016. Bao says the decrease in current use of e-cigarettes was particularly significant in people older than 65, women, non-Hispanic whites, people with low incomes, and current cigarette smokers.

“These trends may suggest that some individuals are trying, but not continuing use of e-cigarettes,” says Bao, cautioning that it might be too soon to draw e-cigarette usage trends from only 3 years of data. He says the findings reflect a recent report from the CDC that also shows a decline in the rate of current e-cigarette use among US middle and high school students.

The study also found that fewer current cigarette smokers use e-cigarettes, but that use of e-cigarettes increased among former smokers.

“This pattern may reflect e-cigarette use as adults are transitioning from current to former smokers, but further investigation is warranted,” Bao says.

Finally, the study found the rates of e-cigarette use increased among people who never smoked until using them.

“This is concerning because these never-smokers are being exposed to nicotine and other harmful ingredients through e-cigarettes,” says Bao.