In a recent study, Harvard public health researchers decided to test a few dozen types of electronic cigarettes for diacetyl, a flavoring chemical associated with a severe respiratory disease known as “popcorn lung.” The researchers found diacetyl in a majority of the e-cigarettes they tested. News outlets jumped on the findings, with some announcing that e-cigarettes could cause the often-debilitating respiratory disease.

But scientist Joseph Allen wants to be clear: His study doesn’t make a definitive statement about the effect of diacetyl in e-cigarettes. Instead, Allen said his goal was to elevate concerns about potentially harmful flavoring chemicals within larger conversations about e-cigarette safety and regulation.

“The reality is that the research is so nascent that we don’t know much about the risks of inhaling these flavoring chemicals,” Allen, an assistant professor in the Harvard T.H. Chan School of Public Health and director of the university’s Healthy Buildings Program, told me. “Our goal is to help make sure that flavorings are now part of the discussion.”

To conduct the study, which was published earlier this month in Environmental Health Perspectives, Allen and his research colleagues selected 51 types of flavored e-cigarettes sold by leading brands and which contained flavors that appeal to young people, such as cotton candy, tutti frutti and cupcake. They tested the products for diacetyl as well as flavoring chemicals acetoin and 2,3-pentanedione, which have also been tied to health risks in the workplace. In particular, diacetyl has been linked to severe respiratory disease in workers who inhale the flavoring chemical. Even more specifically, the chemical has been linked to severe bronchiolitis obliterans, an irreversible loss of respiratory function that can become so bad that its sufferers may require a lung transplant. The diacetyl-linked illness was first documented in workers who were exposed to the butter flavoring in popcorn processing factories, hence the term “popcorn lung.” (A recent news investigation also found worrisome levels of diacetyl exposure in the coffee roasting industry.)

Study authors Allen, Skye Flanigan, Mallory LeBlanc, Jose Vallarino, Piers MacNaughton, James Stewart and David Christiani write:

The heating, vaporization and subsequent inhalation of these flavoring chemicals in e-cigarettes makes an exposure pathway for these flavorings that has significant similarities to those of the workers at the microwave popcorn facilities. …Based on the widespread use of these food flavors across many industries and knowledge that specific chemicals/artificial flavors were developed to mimic certain natural flavors commonly used in e-cigarettes, we hypothesized that these compounds are likely used in the manufacturing of flavored e-cigarettes. We sought to expand the state of knowledge on flavoring chemicals in e-cigarettes with a particular focus on e-cigarettes sold by the largest cigarette companies and also those flavors that we deem would be appealing to children, teenagers and young adults.

To analyze the 51 types of flavored e-cigarettes chosen for the study, the researchers inserted each one into a sealed chamber attached to a device that drew air from the e-cigarette for eight seconds at a time. Here’s what they found: At least one of the three chemicals was found in 47 of the 51 flavors tested. Diacetyl was found in 39 flavors tested, while acetoin and 2,3-pentanedione were detected in 46 and 23 of the flavors, respectively. In addition to detecting diacetyl in e-cigarette flavors that may particularly appeal to young people, it was also found in flavors such as “tobacco” and “menthol.”

Both the Flavoring and Extract Manufacturers Association of the United States as well as the U.S. Occupational Safety and Health Administration recognize the risks of inhaling diacetyl, Allen noted. The association recommends that workers be warned about the potential risks of inhaling such flavoring chemicals, while OSHA has established a National Emphasis Program focused on popcorn processing workers, though the agency has not yet established a Permissible Exposure Limit for diacetyl. However, the National Institute for Occupational Safety and Health and the American Conference of Governmental Industrial Hygienists have issued recommended worker exposure limits for diacetyl.

And Allen said that’s precisely what concerns him. In other words, if workers are being cautioned about exposures they may experience eight hours a day, five days a week, what does that mean for consumers of e-cigarettes who may be inhaling these chemicals for many more hours and with fewer breaks in between? Allen’s study doesn’t reveal the answer to this question, but he said knowing more about the chemical content of e-cigarettes will at least help consumers make more informed choices.

“These warnings are being given to workers, but not to consumers,” Allen told me. “So we hope this kind of research will raise awareness about the potential hazard.”

In conclusion, Allen and his study colleagues write that “urgent action is recommended to further evaluate the extent of this new exposure to diacetyl and related flavoring compounds in e-cigarettes.” As for the next phase in Allen’s research, he’s received funding to expand the sample of e-cigarettes tested and study the effect of e-cigarette vapors on upper airway cells.

“We want to better understand the risk,” he told me. “We just don’t have enough information yet to determine a safe level of exposure…and yet we have more than 1 million kids trying e-cigarettes.”

Currently, the U.S. Food and Drug Administration’s authority to regulate tobacco products does not extend to e-cigarettes. However, proposed regulations that would bring the products under FDA’s authority are currently in review. Members of Congress recently rejected an attempt to include a provision in the budget agreement that would have curbed FDA’s authority over e-cigarettes.

To download a full copy of the new e-cigarette and diacetyl study, visit Environmental Health Perspectives.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.

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