E-cigarettes are a topic of contentious debate. Are they an effective way to wean smokers off of traditional cigarettes? Are their dangers understated? Are they “gateway” devices to tobacco products? In short, all things considered, do e-cigs benefit or denigrate public health?

Earlier this month, a new PLoS ONE study entered into this contentious fray, and its results were fairly damning to claims that e-cigarettes are relatively safe.

To sum the study up: A research team primarily based out of Johns Hopkins University exposed mice to enough e-cigarette vapor so that the levels of cotinine – a metabolite of nicotine and biomarker for tobacco smoke exposure – in their blood was roughly similar to the amount of cotinine seen in the blood of e-cig users.

They found that mice which reached these levels of blood cotinine after exposure to e-cig vapor had compromised immune systems and were more susceptible to viral and bacteria infections compared to mice only exposed to normal air.

“Despite the common perception that E-cigs are safe, this study clearly demonstrates that E-cig use, even for relatively brief periods, may have significant consequences to respiratory health in an animal model; and hence, E-cigs need to be tested more rigorously, especially in susceptible populations,” the researchers concluded.

Their cautionary message was blared across the web, in outlets like Discovery News, The Guardian, the BBC, and The Verge, and was widely shared on social media.

But it seems, however, there’s a “little” problem with the study that escaped the scrutiny of early reporting. Mice have vastly higher rates of cotinine metabolism than humans.

While the half-life of cotinine in mice is roughly 35 to 50 minutes, the half-life of cotinine in humans is approximately 20 hours! This massive disparity means that mice have to be exposed to much higher amounts of e-cigarette vapor at faster rates in order to reach comparable cotinine levels to humans.

In a detailed comment posted to the original study last Thursday, Drs. Alexey Mukhin and Jed Rose from the Center for Smoking Cessation at Duke University Medical Center pointed out this key tidbit of information, and subsequently calculated, based on the study’s methods, how much nicotine the mice were exposed to.

Then they translated that amount to a daily exposure for a human, which ended up being between 300mg and 370 mg per day.

Source: PLOSONE