Flavouring and additive ingredients used in e-cigarettes are more likely to increase inflammation and impair lung function, according to new research.
E-cigarettes -- popular battery-powered devices that simulate the act of smoking a traditional cigarette -- dispense a vapour derived from liquid chemicals in a refillable cartridge.
Researchers from the University of Athens found that short-term exposure to e-cigarettes was enough to cause lung inflammation similar or worse than that seen in traditional cigarette use.
The study, published in the American Journal of Physiology - Lung Cellular and Molecular Physiology, examined several groups of mice that received whole-body exposure to varying chemical combinations four times each day.
Each exposure session was separated by 30-minute smoke-free intervals.
One group was exposed to cigarette smoke, another with e-cigarette vapour containing propylene glycol and vegetable glycerol -- an odourless liquid derived from plant oils, the third with e-cigarette vapour containing propylene glycol and nicotine and another group was exposed to e-cigarette vapour containing propylene glycol, nicotine and tobacco flavouring.
The findings suggested an increase in markers of inflammation, mucus production and altered lung function in the propylene, propylene plus nicotine and flavouring groups after three days.
In addition, two inflammation-producing proteins became elevated only in the flavouring group, which suggested that some flavouring components on the market may not be safe for even short-term use.
The level of oxidative stress -- stress at a cellular level -- in the flavouring group was equal to or higher than that of the cigarette group.
However, respiratory mechanics were adversely affected only in mice exposed to cigarette smoke and not to e-cigarette vapour after prolonged treatment.
"The observed detrimental effects in the lung upon (e-cigarette) vapour exposure in animal models highlight the need for further investigation of safety and toxicity of these rapidly expanding devices worldwide," the researchers warned.