Flavoring and additive ingredients in e-cigarettes may increase inflammation and impair lung function, according to new research. The study, published ahead of print 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. The research was chosen as an APSselect article for October.
E-cigarettes, popular battery-powered devices that simulate the act of smoking a traditional cigarette, dispense a vapor derived from liquid chemicals in a refillable cartridge. The refills typically contain propylene glycol, nicotine and often flavorings. Propylene glycol--a colorless, odorless food additive--is found in numerous processed food and beverages; it is also used as a solvent in a number pharmaceuticals. 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.
- One group was exposed to cigarette smoke ("cigarette");
- One group was exposed to e-cigarette vapor containing propylene glycol and vegetable glycerol, an odorless liquid derived from plant oils ("propylene");
- One group was exposed to e-cigarette vapor containing propylene glycol and nicotine ("propylene + nicotine") and
- One group was exposed to e-cigarette vapor containing propylene glycol, nicotine and tobacco flavoring ("flavoring").
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 vapor (three days), while others were exposed for a longer term (four weeks).
The research team found an increase in markers of inflammation, mucus production and altered lung function in the propylene, propylene + nicotine and flavoring 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 flavoring group, suggesting that some of the many flavoring 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 flavoring 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 vapor after prolonged treatment. "The observed detrimental effects in the lung upon [e-cigarette] vapor exposure in animal models highlight the need for further investigation of safety and toxicity of these rapidly expanding devices worldwide," the researchers wrote.