WASHINGTON — A major new study provides the strongest evidence yet that vaping can help smokers quit cigarettes, with e-cigarettes proving nearly twice as effective as nicotine gums and patches.

The British research, published Wednesday in the New England Journal of Medicine, could influence what doctors tell their patients and shape the debate in the U.S., where the Food and Drug Administration has come under pressure to more tightly regulate the burgeoning industry amid a surge in teenage vaping.

“We know that patients are asking about e-cigarettes and many doctors haven’t been sure what to say,” said Dr. Nancy Rigotti, a tobacco treatment specialist at Harvard Medical School who was not involved in the study. “I think they now have more evidence to endorse e-cigarettes.”

At the same time, Rigotti and other experts cautioned that no vaping products have been approved in the U.S. to help smokers quit.

Smoking is the No. 1 cause of preventable death worldwide, blamed for nearly 6 million deaths a year. Quitting is notoriously difficult, even with decades-old nicotine aids and newer prescription drugs. More than 55 percent of U.S. smokers try to quit each year, and only about 7 percent succeed, according to government figures.

Electronic cigarettes, which have been available in the U.S. since about 2007 and have grown into a $6.6 billion-a-year industry, are battery-powered devices that typically heat a flavored nicotine solution into an inhalable vapor.

Most experts agree the vapor is less harmful than cigarette smoke since it doesn’t contain most of the cancer-causing byproducts of burning tobacco. But there is virtually no research on the long-term effects of the chemicals in the vapor, some of which are toxic.

At the same time, there have been conflicting studies on whether e-cigarettes actually help smokers kick the habit. Last year, an influential panel of U.S. experts concluded there was only “limited evidence” of their effectiveness.