take a number: From 0 to 10 Million: Vaping Takes Off in the U.S.

Some experts have suggested that e-cigarettes can help wean people off regular cigarettes; others believe that they reinforce the smoking habit and increase the user’s exposure to nicotine.

But there’s no dispute that e-cigarettes have grown popular since their introduction in 2004. Now a nationwide survey has found that 10.8 million adults in the United States are vaping.

The analysis, published in the Annals of Internal Medicine, found that 54.6 percent of e-cigarette users were also smoking cigarettes. About 15 percent of vapers had never smoked cigarettes, and 30.4 percent had quit smoking them.

The study is based on data from the Behavioral Risk Factor Surveillance System, a national survey conducted by the Centers for Disease Control and Prevention. In 2016, the researchers surveyed 486,000 people 18 and older by telephone in every state and the District of Columbia, as well as Guam, Puerto Rico and the Virgin Islands.

More than half of e-cigarette users were younger than 35, and the prevalence decreased with increasing age. It was highest among people ages 18 to 24, both occasional and daily users.

Over all, almost 6 percent of men and 3.7 percent of women were vaping. But there were sharp differences among particular demographic groups.

The prevalence was 9 percent among bisexuals, for example, and 7 percent among lesbians and gay men, compared with 4.6 percent among heterosexuals. Almost 9 percent of transgender people were vapers.

People with cardiovascular disease, cancer, asthma and depression were also more likely than others to be using e-cigarettes, and the rate was 10.2 percent among people with chronic obstructive pulmonary disease. Almost 2 percent of pregnant women were vaping.

[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]

E-cigarettes were most commonly used in Oklahoma and in the Southeast, and least often used in North Dakota and California.

“The use of e-cigarettes in the U.S. is a complicated picture,” said the study’s senior author, Dr. Michael J. Blaha, an associate professor of medicine and epidemiology at Johns Hopkins.

“People who try e-cigs are at risk for a variety of health conditions. But you have former smokers, daily smokers, occasional smokers — it’s going to be difficult to sort out the health effects.”

Dr. Blaha added, “Almost everyone would agree that the use of e-cigarettes among people who have never smoked — we’re up to almost 2 million people — is something we have to watch very carefully.”

He and his colleagues acknowledge that the study depends on self-reports and demonstrates only associations, not cause and effect. Moreover, the researchers had no data on the type of e-cigarette device used, the flavors added or the size of the nicotine dose.