A new piece of research from Dr. Konstantinos Farsalinos and his colleagues has investigated the potential cytotoxicity of e-cigarette vapor, and found that (shockingly enough) the vast majority of vaporized liquids are much safer than the smoke from traditional cigarettes.
This is also the first study to investigate the effects of vaping at higher voltages, a common practice amongst dedicated vapers (using mods or APVs), marking what is hopefully the first of many more detailed analysis of the differences in safety of various e-liquids and devices. The study is available online for free, and provides some tantalizing results which are ripe for further investigation.
Cytotoxicity is a measure of a substance’s potential to kill or damage cells, and cigarette smoke has long been known to fall into this group.
Researchers tested the vapor from 20 e-liquids (under ordinary vaping conditions) and cigarette smoke on in vitro cultured heart cells to determine the risk in terms of cytotoxicity.
Only four out of the 20 e-liquids produced vapor which crossed the cytotoxicity threshold (less than 70 percent cell viability compared to the control group) in pure extract form, and all aside from one still ranked as safer than the cigarette smoke extract.
A cinnamon-based liquid produced vapor which was just over the threshold for cytotoxicity, and the remaining three liquids were made using an unusual method involving pure tobacco leaf.
High voltage was found to have no significant effect on cytotoxicity, although it did push the liquids slightly closer to the threshold.
Increasing nicotine content didn’t have a significant effect, but also produced a modest difference.
Propylene glycol (PG) and vegetable glycerin (VG) didn’t display cytotoxicity at any level in a 50/50 mixture (with no other ingredients present).
It’s good news for vapers, but more research is needed on the risks associated with specific flavorings and e-liquid production methods to ensure the safest e-liquid every time.
Cytotoxicity and Cigarettes
Something which is cytotoxic is something that kills cells or is toxic to cells, and most cancer treatments ultimately fall into this classification. Cigarettes are well-known to be cytotoxic, and this – like many of the harms associated with smoking – is thought to be related to the complex array of chemicals produced by the burning of the tobacco plant. Cytotoxicity is closely related to oxidative stress, which is basically the result of a barrage of free radicals (each puff on a tobacco cigarette contains around a million billion molecules of these, according to the researchers) which harm a wide range of cells. Since e-cigs don’t involve this combustion, the theory goes that they shouldn’t exhibit the same degree of cytotoxicity.
What They Did
To determine the cytotoxic potential of e-liquids, the researchers tested 20 of them on some lab cultured heart cells. This in vitro (literally: in glass) method of testing makes things easier to apply samples and take measurements from, but there is a potential for the results of these tests to not be applicable to in vivo (in a human; or literally: in the living) scenarios. However, the level of applicability of these tests can be estimated because they also tested cigarette smoke in the same way, and there is plenty of in vivo data for cigarettes which the results can be compared with.
The e-liquids were tested in vapor form, and were taken from a variety of suppliers. The full list is available in the study, but the most notable were the testing of a base mixture (PG and VG in a 50/50 ratio, nothing else) and the liquids from UK-based producer House of Liquid, who make their tobacco flavors by soaking actual tobacco leaves in an e-liquid base. All of these e-liquids were tested with a Joyetech eGo (at 6.2 Watts) and four were randomly selected to be tested on the Lavatube at a higher wattage (9.2 W).
The focus was on the results in comparison to a Marlboro cigarette, and they aimed to get consistent performance by fully charging the batteries each time and replacing the atomizer for each test. Additionally, an experienced vaper (who was on the research team) was assigned to test the e-cigs for “dry puffs” – which causes that horrible burnt taste you get when there isn't enough liquid in the wick. This enabled the tests of the e-cigs to be under realistic conditions (since you wouldn't keep puffing on a dry wick for as long as you would a moist one) – with the only difference being that the length of the puffs was reduced from four seconds (as it was on the eGo) to 2.5 seconds on the Lavatube to account for this. They also allowed for a realistic interval between puffs to make it more applicable to everyday vaping habits.
The basic method of the experiment is that once the vapor and smoke had been turned into extracts (of varying potency), they were tested on cultured heart cells to see the rate of cell death produced. They also left some identical cells untreated (as a control), so the “viability” (the number of healthy cells remaining) of the experimental samples could be expressed as a percentage (with the viability of the untreated cells being set as 100 percent). Any viability result lower than 70 percent is classified as cytotoxic, according to accepted definitions.
What they Found
Unsurprisingly, the e-liquid vapor performed much better than the cigarette smoke on the whole. Cigarette smoke was cytotoxic at any tested concentration over 12.5 percent (which came out at an unambiguous 38.2 percent), and produced a viability of 3.9 percent when the pure extract was used. In comparison, even when using pure extract, only four out of the 20 liquids tested reached cytotoxicity, with the cinnamon cookies liquid, for example, producing a viability of 64.8 percent. The remaining three liquids which were cytotoxic when pure extract were produced by House of Liquid using actual tobacco leaf. A more typical cytotoxicity result for pure e-liquid vapor is that for Alter Ego’s City liquid, which led to cell viability of 93.6 percent – over 20 times better than the tobacco cigarette smoke.
The four samples which were selected to be tested at a high voltage didn’t display any significant differences in the potential for cell death. The viability percentages dropped across the board (indicating a slight increase in risk from higher wattages) but none of them went below the 70 percent mark, even when cultures were exposed to the pure vapor extract. The results for differing nicotine levels were similar, with pure extract tests of high nicotine levels causing a drop in viability but not to cytotoxic levels. The bases (PG and VG) were never cytotoxic, and the concentration of the extract had little impact on this – if anything, higher concentrations produced more favorable results!
The results they obtained for the testing on cigarettes was in line with what is known from existing research, so although in vivo data would be useful, there is no reason to think the results of this test were notably affected by the artificial environment of the tests.
What it Means
In basic terms, the study shows that the main factor which influences the impact of e-cig vapor on cell toxicity is actually the specific flavorings used. The minor cytotoxicity of the cinnamon-based sample, for example, is in line current knowledge about the potential risks of cinnamon oils, but the result was still over 10 times better than the cigarette sample. The worst results came from the House of Liquids samples, where one liquid (El Toro Puros – 24 mg) was actually worse in pure extract form than tobacco cigarette smoke (a viability of 2.2 percent).
This appears to be related to the unique process mentioned earlier, and the assumption is that other dangerous chemicals from tobacco may wind up in the liquid as a result. The researchers note that although the resulting solution is filtered before being bottled as e-liquid, impurities could still seep through. The fact that one liquid produced in this way was not cytotoxic is a little confusing, but this is thought to be related to the different leaves used to make it.
So the implications of this research are very positive. There are small risks to some e-liquids, but this isn't related to the core ingredients (nicotine, PG and VG), but to specific flavorings – notably cinnamon. The worst results from the e-liquids come from an unusual and understandably more risky process, and the more information researchers are able to uncover about the reasons for this discrepancy, the safer e-liquids will become. The researchers do also note the chance that e-liquids produced from nicotine extracted using a cheaper method may also carry this risk. However, the vast majority of flavors don't appear to carry this risk.
The overarching conclusion to this piece of research is that unlike cigarettes, the vast majority of e-liquids don't provoke cell death, regardless of the nicotine content or the voltage you're vaping at. For researchers, further investigation into the areas of minor risk can only improve the situation, but for almost all individual vapers the risk has yet again been shown to be minimal. Perhaps it'd be prudent to avoid House of Liquids’ tobacco options and use cinnamon flavors sparingly, but realistically this research is very good news for vapers indeed.