(CNN) Hobbits toke on pipes in the Shire. James Bond smokes while outsmarting foes and wooing women. Freddie Mercury and his bandmates puff on cigarettes as Queen rockets to stardom.

The lead characters in some of the decade's most successful films still smoke on-screen.

The number of times tobacco use appeared on-screen in PG-13 films jumped 120% between 2010 and 2018, according to a new US Centers for Disease Control and Prevention report. The findings come as skyrocketing e-cigarette use erased previous years' progress in ending youth dependence on tobacco.

It's a troubling trend, researchers said, because young people who see more smoking on-screen are more likely to smoke themselves.

The US Surgeon General's Office has long warned of the causal relationship between smoking by characters in youth films and the likelihood of youth tobacco use. When it's portrayed as the "social norm," impressionable children and teens may imitate characters who smoke and perceive smoking as an appealing way to fit in, federal experts say.

Tobacco use remains the leading cause of preventable death in the United States, according to the CDC , mostly because of the wide range of smoking-related illnesses. Lung cancer, heart disease and chronic obstructive pulmonary disease (COPD) are the three most fatal results of smoking and second-hand smoke.

Tobacco use in all films jumped 57%

The CDC counted the number of times tobacco use appeared in top-grossing films (those that made the Top 10 in the week of their release) with data from lung health nonprofit Breathe California Sacramento Region and the University of California, San Francisco's Smoke-Free Movies program

Both programs defined a "tobacco incident" as the use or implied use of tobacco products like cigarettes, pipes or e-cigarettes on-screen.

Overall, tobacco use onscreen jumped 57% in all films from 2010 to 2018. The most marked jump occurred in PG-13 biographical dramas, at 233%.

Perhaps oddly, researchers said, fictional characters who existed within real stories were the most frequent on-screen smokers.

Meantime, some companies wiped out tobacco use entirely in films for younger audiences. Smoking in Disney and Viacom features dropped to zero by 2018 -- but in films produced by Comcast, tobacco incidents increased nearly 3,000%.

The authors didn't offer an explanation for the jump in on-screen tobacco use but proposed ways to curb it.

Researchers suggested that the Motion Picture Association of America, the body responsible for rating films based on content, dole out R ratings to films with on-screen smoking unless the character smoking is a biographical figure or it portrays the negative effects of smoking.

They also posited omitting smoking from youth-rated films entirely.

Hollywood and smoking: Art or influence?

When talking pictures took off in the 1920s, tobacco companies paid for most of Hollywood's advertising, even holding stars under ad contracts that required them to use the product, according to UC San Francisco's Smoke Free Movies

The US banned advertising of tobacco products in the 1970s, in light of damning federal reports on the health hazards of smoking. So, tobacco companies turned to product placement in popular entertainment until the 1998 Master Settlement Agreement outlawed the practice in TV, film and video games.

Contemporary Hollywood auteurs have defended smoking in film as a purely artistic choice. In a 1999 survey of Hollywood directors and producers, many respondents said making tobacco use part of a character's story was representative of a time period or a personality trait.

But they acknowledged, too, that cigarettes were "props" with specific connotations for characters and audience members -- characters who used them were often played as cool, tough and dangerous.

But that was 20 years ago, when teen smoking reached its peak and before campaigns like the CDC's "Tips from Former Smokers" and Truth Initiative warned young people not to use tobacco.

Tobacco use in film had declined before now

As recently as 2007, on-screen smoking had significantly declined to just 0.23 scenes of tobacco use in the year's highest-grossing films. Teen cigarette use dropped off with it, from 36% of high schoolers in 1997 to 20% in 2007.

But that progress stalled in the 2010s. The highest-earning films featured tobacco use on-screen 80% more in 2016 than in 2015, and teen tobacco use shot back up in 2018 as e-cigarettes grew in popularity, the CDC said

Vape pens feature far less in film than cigarettes do, but they've replaced cigarettes as young people's preferred way to smoke. More than 20% of high school students use vape pens to get their tobacco fix, while 8% smoke cigarettes, the CDC said

Many e-cigarette companies have ditched tobacco for nicotine, which has been linked to an outbreak of lung disease, particularly among teens.