At the heart of the hysteria over vaping is what seems like a simple question: Is it safer than smoking?

Answering that question, however, is complicated. While e-cigarettes contain and produce fewer known cancer-causing toxins than cigarettes, that’s not the only factor at play. There are a host of unknowns about e-cigarettes, largely because long-term studies on their use have not yet been completed, Time magazine says.

A new paper published in the American Journal of Preventive Medicine presents the findings of what’s thought to be the first longitudinal analysis of the association between vaping and lung disease. Researchers tracked e-cigarette users for three years, and found that they had a 1.3-times higher risk of developing respiratory disease than people who did not use any tobacco product. Meanwhile, cigarette smokers had a 2.5-times higher risk, and those who both smoked and vaped had a 3.3-times higher risk.

“If you’re going to do one or the other, in terms of these respiratory effects you’re probably better off with an e-cigarette,” says study co-author Dr. Stanton Glantz, a professor of medicine at the University of California, San Francisco and a leading researcher (and critic) of e-cigarettes. Even still, Glantz cautions that his prior research has found similar levels of cardiovascular risk associated with smoking and vaping; this was outside the scope of the new paper.

“This study actually does support the harm reduction potential of e-cigarettes,” says Andy Tan, an assistant professor of population sciences at Dana-Farber Cancer Institute who has studied e-cigarettes. “Yes, vaping is associated with about 29% to 31% higher odds of subsequent lung disease within two to three years than not vaping—but compare this with the 156% higher odds of using combustible tobacco than not smoking.”