SAN DIEGO — Heavy exposure to electronic cigarette vapor damages DNA in cell cultures, causing genetic instability that could lead to cancer, according to a study by VA San Diego Healthcare System and University of California, San Diego, researchers.

Moreover, even nicotine-free vapor induces this damage, indicating that other substances in e-cigarettes can damage cells, the study stated.

The study won’t come close to scientifically settling whether e-cigarettes represent a great new danger, a harmless diversion or something in between. It does provide more grounds for suspicion that e-cigarettes are not entirely benign and carry health risks of an unknown magnitude.

Worldwide attention has been focused on e-cigarettes as a possible means of weaning smokers off tobacco, or alternatively as a new public health menace. But since e-cigarettes became popular scarcely a decade ago, there hasn’t been time to collect long-term evidence, such as the population studies that linked smoking to lung cancer.

The study was published Dec. 28 in the journal Oral Oncology. Weg M. Ongkeko was the senior author on the research team, and Vicky Yu was first author.

The new research doesn’t prove the damage takes place in people, because it was performed only in cell cultures, said Laura Crotty Alexander, one of the research team study authors. But it strongly suggests such an effect takes place. Further work is needed to confirm this damage and at what levels of exposure to e-cigarette vapor the damage kicks in.

She has previously conducted e-cigarette research indicating the vapor makes the “superbug” MRSA harder to kill.

An even bigger question, whether e-cigarettes are as bad for one’s health as regular cigarettes, also isn’t answered in the study, Crotty Alexander said. That question bedevils public health advocates who are wrestling with the issue of how to deal with e-cigarettes.

In a statement that made headlines around the world, Jessica Wang-Rodriguez, another study author, said e-cigarettes “are no better than smoking regular cigarettes.”

That statement was made in a news release picked up by reporters who didn’t cite from the study itself. These news release rewrites were strongly criticized by other researchers.

“To declare that smoking is no more hazardous than using e-cigarettes, a non-tobacco-containing product is a false and irresponsible claim,” e-cigarette researcher Michael Siegel of Boston University told the Daily Caller.

Crotty Alexander said the evidence simply isn’t definitive, in any direction.

“The problem is that we really cannot say that the e-cigarettes are safer in humans,” Crotty Alexander said. “I feel uncomfortable saying that e-cigarettes are equally bad or worse than conventional combustible cigarettes, but that is some people’s opinion.”

The paper notes that cigarette smoke extract kills cells at a lower concentration than does e-cigarette vapor, Crotty Alexander said. And it kills more rapidly.