Despite decades of declining cigarette use, one in four U.S. adults still use a tobacco product at least occasionally, the Centers for Disease Control and Prevention reports.

Cigarettes remain the most popular overall, but hookah and e-cigarette use was most common among 18- to 24-year-olds. It is the most troubling finding from the report, said Douglas E. Jorenby, Ph.D., a nicotine addiction researcher at the University of Wisconsin.

Information about the health risks of emerging tobacco products is scant because American scientists have been slow to recognize the recent “revolution in terms of how people are getting nicotine and tobacco,” said Jorenby, a professor of medicine and director of clinical services at the university’s Center for Tobacco Research and Intervention.

Researchers do not yet know the long-term effects of e-cigarettes and hookahs on cardiovascular health. The first U.S. studies looking at the health impact of e-cigarettes and hookahs only go back about five years, he said.

“Smoking is a leading preventable cause of cardiovascular disease,” said Jorenby, who was a social smoker during college.

For the report, published last week in the CDC’s Morbidity and Mortality Weekly Report, researchers analyzed results from the 2013-2014 National Adult Tobacco Survey. More than 49 million U.S. adults — about 21 percent — reported using a tobacco product every day or some days. Cigarettes were used by 17 percent of adults; smokeless tobacco by 2.5 percent; e-cigarettes by 3.3 percent; and hookahs by 0.6 percent.

When researchers included those who reported only rarely using tobacco, the number of users rose to nearly 59 million — a quarter of U.S. adults.

Among the other findings:

  • Tobacco use was highest among 25- to 44-year-olds and lowest among seniors.
  • Gay, lesbian and bisexual adults are much more likely to use tobacco than heterosexual adults: 32 percent compared to 21 percent.
  • Blacks and whites are more likely than Asians and Hispanics to use tobacco products.
  • Men are more likely than women to use tobacco.
  • Americans living in the Midwest and South are more likely to use tobacco.

The National Adult Tobacco Survey first collected data in 2009-2010. Hookah use has been tracked since then, and e-cigarette use since 2012.

The progress made over the past five decades to curb smoking rates must now address a more diverse landscape of tobacco products, the researchers said.

Strategies such as “tobacco price increases, high-impact anti-tobacco mass media campaigns, comprehensive smoke-free laws, and enhanced access to help quitting tobacco use, in conjunction with FDA regulation of tobacco products, are critical to reducing tobacco-related diseases and deaths in the United States,” the authors wrote.

In May, the Food and Drug Administration issued new rules for e-cigarettes, hookahs and other previously unregulated tobacco products. The new regulations take effect next month.