As e-cigarettes rise in popularity, many researchers are working hard to understand the long-term implications of vaping on human health. A new small study led by a team at the University of Birmingham has now found that e-cigarette vapor can damage key immune cells in the lung, suggesting vaping may be more harmful that previously suspected.

The new study was conducted on lung tissue samples in a laboratory. The experiments revealed that when exposed to artificially vaped e-cigarette condensate, alveolar macrophages, a type of immune cell that importantly helps keep our respiratory tract clear of harmful particles, displayed impaired activity.

Exposure to the vaped condensate also boosted production of free radicals and increased cell death. These effects were noted to be even more heightened when the condensate contained nicotine.

"Importantly, exposure of macrophages to [e-cigarette vapour condensate] induced many of the same cellular and functional changes in [alveolar macrophage] function seen in cigarette smokers and patients with COPD (chronic obstructive pulmonary disease)," the researchers write in their study.

It's important to note that these results have only been demonstrated in cellular studies in laboratory conditions. Replicating the results in real-life conditions may prove difficult, meaning it is unclear what duration or dose of e-cigarette vapor will cause these results in human subjects. Ultimately, the big question hovering over much of this new e-cigarette research is what the long-term effects of vaping actually are on human beings.

"In terms of cancer causing molecules in cigarette smoke, as opposed to cigarette vapor, there are certainly reduced numbers of carcinogens," explains lead author on the new study, David Thickett. "They are safer in terms of cancer risk, but if you vape for 20 or 30 years and this can cause COPD, then that's something we need to know about."

Jonathan Grigg, from the Queen Mary University of London, did not work on this new study but suggests it adds to a growing body of evidence affirming e-cigarettes may not be as fundamentally harmless as many have claimed in the past.

"The argument that, since vaping is better than smoking cigarettes any effects of vape on lung cells are not important – is increasingly becoming a specious one," says Grigg.

Thickett does confirm that he doesn't believe e-cigarettes are more harmful that regular cigarettes but he does add, "we should have a cautious skepticism that they are as safe as we are being led to believe."

The new research was published in the journal Thorax.