Flavouring and additive ingredients in e-cigarettes may increase inflammation and impair lung function, according to a study.
The research, published in the American Journal of Physiology -- Lung Cellular and Molecular Physiology, also found that short-term exposure to e-cigarettes was enough to cause lung inflammation similar or worse than that seen in traditional cigarette use.
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.
The refills typically contain propylene glycol, nicotine and often flavourings, said researchers from the University of Athens Medical School in Greece.
Propylene glycol -- a colourless, odourless food additive -- is found in numerous processed food and beverages; it is also used as a solvent in a number pharmaceutical.
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E-cigarette devices and refills are not well regulated, and the long-term health effects of e-cigarette use are not widely known.
Researchers studied 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.
The cigarette and e-cigarette groups were compared with a control group that was exposed to medical-grade air.
Some of the animals in each group were exposed to short-term cigarette smoke or e-cigarette vapour (three days), while others were exposed for a longer term (four weeks).
The team found an increase in markers of inflammation, mucus production and altered lung function in the propylene, propylene + nicotine and flavouring groups after three days.
However, the propylene group showed fewer negative effects with long-term exposure, suggesting the additive alone elicits only a temporary irritation that eventually subsides with continued use.
In addition, two inflammation-producing proteins became elevated only in the flavouring group, suggesting that some of the many flavouring components on the market may not be safe for even short-term use.
The condition of the e-cigarette groups in comparison with the cigarette group surprised the researchers. 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 said.
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