Vaping is touted as a lesser of two evils for smokers trying to quit - but a Kiwi scientist says there's much about e-cigarettes' long-term effects that we still don't know.
The University of Auckland's Dr Kelly Burrowes has now launched the most advanced study of its kind in the world, using human trials and state-of-the-art 3D computer models to get a precise look at what vaping does to our lungs.
Worldwide sales of e-cigarettes have boomed around the globe over the past decade, and today an estimated three in 100 Kiwis use them at least once a day.
The Ministry of Health's Vaping Facts website advises e-cigarettes are less harmful than smoking - but points out they haven't been around long enough for the long-term effects to be known.
Burrowes said that, given they're being promoted here as a tool to reach New Zealand's Smokefree 2025 targets, regulators and healthcare providers needed to know the devices indeed reduced harm caused by smoking - and didn't just pose further risks.
And there was mounting evidence that there were indeed risks.
One recent animal study showed an increase in lung cancer development as a result of exposure to nicotine containing e-cigarette aerosol, while another pointed to emphysema-like changes in lungs after use.
Burrowes, a leading bioengineer, also highlighted a 2019 outbreak that hospitalised around 3000 people in the US - thought to be the result of vitamin E acetate being added to THC-containing vaping liquids.
Vaping devices work by using heat to aerosolise a liquid - typically consisting of propylene glycol, glycerol, flavourings and nicotine - that's then inhaled and puffed out.
"All of the chemicals used are generally regarded as safe for oral ingestion - but their impact on the lungs, and the rest of the body, when inhaled is unknown," she said.
"In addition, analysis of the chemicals in electronic cigarette aerosol have shown a much larger range of chemicals than those in the liquid."
In earlier research, Burrowes and her colleagues have identified about 50 different chemicals - including heavy metals that most likely come from the metal-heating coil and welding material within the devices.
Some studies have also shown carcinogenic chemicals within the aerosol, including formaldehyde and acrolein, which are created as by-products through the heating process.
"You may have seen the value of '95 per cent safer' being used, especially by retailers," she said.
"This quantification is completely unfounded because the data required to make this quantification are not yet available."
That metric came from a study that estimated the relative harms of nicotine-containing products, which used scoring from a selected panel of experts.
"While the scores provided by the panellists were informed by knowledge, they are fundamentally value judgements and are not an exact science."
However, the devices have shown promise in quit-smoking studies - and some research has also indicated smokers with Chronic Obstructive Pulmonary Disease could see improvements in lung function if they switched to vaping.
On the weight of evidence so far, Burrowes felt vaping were likely useful aids for quitting cigarettes - but should only be used as an intermediate step.
Burrowes' new study, supported by a new Marsden Fund grant, sought to find out exactly what went into vaping aerosols, where these chemicals travelled in the body, and what effect they had on everything from cells to whole organs.
With more than 400 vaping brands and 8000 flavours - not to mention other factors like different device settings - getting a catch-all picture wasn't easy.
But Burrowes' team has already developed a device that controlled for all of those variables - and they'd use it to gain the data needed to build rich new models.
The first stage of the project used sophisticated methods, such as gas chromatography-mass spectrometry, to measure the inhaled chemicals, alongside other measurements of particle sizes.
Investigating how the aerosol made its way into our lungs would be similarly challenging.
For this, the team would test their computer models - and actual particle flows - against 3D-printed models of our airway tree.
The next steps will involve looking at how cells, tissues and lungs responded, by observing 20 healthy young volunteers before and immediately after vaping.
The scientists expected that, like cigarette smoke, vaping triggered an inflammatory response in the lungs that changed their function and density - and their mechanics over time.
"There is currently no way to link from changes occurring at the cellular level to the impact on how the lungs work as a whole to really understand the impact of vaping – our models will be the first in the world to do this" Burrowes said.
The most impressive part of the project was in its computational modelling.
"Our models of the lung are known around the world as the most advanced and realistic of their kind - we have the only model of the lungs that looks and breathes like a real lung."
She expected these insights could ultimately inform future policy.
"Electronic cigarettes could have a significant positive impact on our society through smoking reduction - but their net health impact depends on risks that are poorly understood, as well as their benefits," she said.
"Both must be understood for meaningful regulation."