The debate over electronic cigarettes has been sparked once again with a new study claiming the alternative is safer and less toxic than regular cigarettes.

Scientists at University College London determined that smokers who substituted e-cigs for the real thing had lower levels of toxic and cancer-causing substances in their bodies.

Read: Smoking vs. Vaping 2016: 4 Facts And Myths About E-Cigarettes And Health

In the study, exposure to tobacco-related chemicals was measured in the saliva and urine of long-term smokers as well as e-cigarette and nicotine replacement therapy users. Those who stopped smoking and picked up one of the proxies had significantly lower levels of chemicals in their bodies compared to those who didn’t. However, smokers who supplemented cigarettes with one of the other options did not benefit from the same reduction. Published in the Annals of Internal Medicine, the investigation consisted of 181 participants over the course of six months.

“Our study adds to existing evidence showing that e-cigarettes and NRT are far safer than smoking, and suggests that there is a very low risk associated with their long-term use,” says Dr. Lion Shahab, lead author, in a statement.

However, these findings are at odds with recent e-cigarette news. In another paper published last month, researchers at Johns Hopkins found the presence of potentially toxic and carcinogenic metals in first generation e-cigarette liquids. The liquid is the component that delivers nicotine and flavors to smokers when heated. A study released last week indicates that habitual e-cigarette smokers exhibited two biological markers associated with heart disease, raising additional concerns about the habit.

“One of our biggest worries is it’s too soon to know,” says Ana María Rule, Ph.D, of Johns Hopkins School of Public Health, and lead author of the e-cigarette metals research.

Read: E-Cigarettes’ Effect On The Immune System Could Make Them No Better Than Regular Cigarettes

She tells  Medical Daily that for many public health professionals, long-term means 10 to 20 years, and vaping just hasn't been around for long enough to determine the lasting effects.

While many e-cig advocates claim it’s a less-risky alternative, the doctor isn’t so sure. “In the short term, it appears that they are,” she says. “But we are finding metals that are not present in cigarettes. We know that there are long-term effects of these metals.” She says that it could take 10 to 20 years of exposure to observe the effects from the materials.

For those trying to wean themselves off of traditional cigarettes, Rule cautions that users often find themselves hooked on e-cigs as they contain nicotine, however, she has found that some are successful when they continually lower the dosage of the addictive substance.

This research can be confusing for consumers as the results seem to be at odds with each other. Rule says the main takeaway is that it’s too soon to tell and advises people to proceed with caution. “We don’t know,” she says about e-cig safety. “It’s risky.”

See Also:

E-Cigarettes May Be Safer Than Tobacco Cigarettes When It Comes To Formaldehyde; Should We Be Skeptical?

Vaping Health Effects: Dangerous Chemicals Discovered In Flavored E-Cigarette Vapor