Reports of lung injuries from e-cigarettes splash across the news these days, but the nicotine-delivery devices are also spawning a quieter worry: whether users risk long-term health effects that may not manifest for decades. Studies in animals and people are now starting to probe whether e-cigarettes pose chronic risks to the lungs and cardiovascular system and how the chemicals they contain might disrupt healthy biology.
E-cigarettes are battery-powered devices containing nicotine and other substances, such as solvents that dissolve the nicotine and flavorings that enhance their appeal. Heat converts the mix into an aerosol that users inhale. Manufacturers tout e-cigarettes as tools to help smokers quit, although data are mixed. But one thing is clear: Millions of young people who didn't smoke cigarettes have taken up vaping. And given that e-cigarettes vary more than conventional cigarettes in their chemical composition, "We're asking medical science to do a huge, heavy lift" to pinpoint health impacts across people, says James Stein, a preventive cardiologist at the University of Wisconsin in Madison.
He and others believe they have no choice but to try. This month, the National Heart, Lung, and Blood Institute gave a boost to studies of acute and chronic effects when it announced supplemental funds for ongoing e-cigarette research, on which the institute spent $23 million this year.
E-cigarettes have been around in some form for decades but began to soar in popularity about 5 years ago, thanks to thousands of flavoring options and new delivery methods that more closely mimic smoking. Today, about 13 million people in the United States use them, as do millions more worldwide. In March, one hazard emerged when acute lung injuries began to strike; U.S. cases now approach 2300, with 47 deaths. "We were all taken by surprise" by those lung injuries, says Peter Shields, a medical oncologist who specializes in lung cancer at Ohio State University's Comprehensive Cancer Center in Columbus. They look unlike anything seen in cigarette smokers. Health officials now suspect the injuries are linked to a vitamin E oil added to e-cigarettes containing tetrahydrocannabinol, better known as THC.
Animal studies are already yielding clues about longer term effects of e-cigarette use. In September, a paper in The Journal of Clinical Investigation described mice exposed to e-cigarettes for 4 months, nearly one-quarter of their life span. Farrah Kheradmand, a pulmonologist at Baylor College of Medicine in Houston, Texas, who led the work, says that, at first, "There was absolutely no emphysema, nothing" in the animals that inhaled aerosol from e-cigarettes. That finding jibes with earlier research showing combustion products are the cause of airway inflammation in smokers.
Then Kheradmand's graduate student Matthew Madison showed her slides of the animals' lung tissue. She did a double take. Immune cells called macrophages were swollen with fat, an abnormality. Kheradmand guessed at first that the cells had gorged on vegetable glycerin, which is used as a solvent in vaping liquids. But when the scientists cracked open the macrophages, they found they were mistaken. "I couldn't sleep at night," Kheradmand says. "Where is this fat coming from?"
Further experiments revealed a likely explanation. Macrophages protect the body from infections, but they also help recycle lung surfactant, a mix of proteins and lipids that coats the inside of lung air sacs and aids gas exchange. Vegetable glycerin and another solvent in e-cigarettes, propylene glycol, are "capable of not only dissolving nicotine, but dissolving anything that comes their way—including the surfactant," Kheradmand says, and her work suggests the macrophages were filled with the type of fat in surfactant. Affected mice seemed healthy, but when Kheradmand exposed them to a flu virus, those with swollen macrophages died, suggesting their ability to battle infection had weakened.
E-cigarettes are battery-powered devices containing nicotine and other substances, such as solvents that dissolve the nicotine and flavorings that enhance their appeal. Heat converts the mix into an aerosol that users inhale. Manufacturers tout e-cigarettes as tools to help smokers quit, although data are mixed. But one thing is clear: Millions of young people who didn't smoke cigarettes have taken up vaping. And given that e-cigarettes vary more than conventional cigarettes in their chemical composition, "We're asking medical science to do a huge, heavy lift" to pinpoint health impacts across people, says James Stein, a preventive cardiologist at the University of Wisconsin in Madison.
He and others believe they have no choice but to try. This month, the National Heart, Lung, and Blood Institute gave a boost to studies of acute and chronic effects when it announced supplemental funds for ongoing e-cigarette research, on which the institute spent $23 million this year.
E-cigarettes have been around in some form for decades but began to soar in popularity about 5 years ago, thanks to thousands of flavoring options and new delivery methods that more closely mimic smoking. Today, about 13 million people in the United States use them, as do millions more worldwide. In March, one hazard emerged when acute lung injuries began to strike; U.S. cases now approach 2300, with 47 deaths. "We were all taken by surprise" by those lung injuries, says Peter Shields, a medical oncologist who specializes in lung cancer at Ohio State University's Comprehensive Cancer Center in Columbus. They look unlike anything seen in cigarette smokers. Health officials now suspect the injuries are linked to a vitamin E oil added to e-cigarettes containing tetrahydrocannabinol, better known as THC.
Animal studies are already yielding clues about longer term effects of e-cigarette use. In September, a paper in The Journal of Clinical Investigation described mice exposed to e-cigarettes for 4 months, nearly one-quarter of their life span. Farrah Kheradmand, a pulmonologist at Baylor College of Medicine in Houston, Texas, who led the work, says that, at first, "There was absolutely no emphysema, nothing" in the animals that inhaled aerosol from e-cigarettes. That finding jibes with earlier research showing combustion products are the cause of airway inflammation in smokers.
Then Kheradmand's graduate student Matthew Madison showed her slides of the animals' lung tissue. She did a double take. Immune cells called macrophages were swollen with fat, an abnormality. Kheradmand guessed at first that the cells had gorged on vegetable glycerin, which is used as a solvent in vaping liquids. But when the scientists cracked open the macrophages, they found they were mistaken. "I couldn't sleep at night," Kheradmand says. "Where is this fat coming from?"
Further experiments revealed a likely explanation. Macrophages protect the body from infections, but they also help recycle lung surfactant, a mix of proteins and lipids that coats the inside of lung air sacs and aids gas exchange. Vegetable glycerin and another solvent in e-cigarettes, propylene glycol, are "capable of not only dissolving nicotine, but dissolving anything that comes their way—including the surfactant," Kheradmand says, and her work suggests the macrophages were filled with the type of fat in surfactant. Affected mice seemed healthy, but when Kheradmand exposed them to a flu virus, those with swollen macrophages died, suggesting their ability to battle infection had weakened.
