A new study found that long-term exposure to nicotine-containing e-cigarette vapor increases the risk of cancer in mice.
This study adds to a growing body of research highlighting the potential negative health effects of vaping.
The researchers caution in a statement that, because this is a mouse study, the results are not meant to show directly what happens in people who vape.
But they argue that the results are concerning enough that, “E-cigarette smoke must be more thoroughly studied before it is deemed safe or marketed that way.”
And it comes as the number of vaping-related lung injuries in the U.S. has grown to 1,299 cases, with 26 confirmed deaths. In those cases, federal officials believe cartridges containing THC may be to blame.
E-Liquid Vapor Linked to Cancer in Mice
In the new study, one group of mice were exposed to nicotine-containing e-cigarette vapor for 20 hours per week for 54 weeks.
After this time, 22.5 percent of the mice developed a type of lung cancer called an adenocarcinoma.
Also, 57.5 percent of these mice developed a rapid growth of cells in the bladder, known as urothelial hyperplasia. This is a type of abnormal tissue growth seen in cancer.
Another group of mice breathed nicotine-free e-cigarette vapor for the same duration. None of these mice developed lung cancer, while 6.3 percent (one mouse) developed bladder hyperplasia.
The researchers also had a control group of mice who breathed only filtered air. One of these mice (5.6 percent of the total) developed a lung tumor after 54 weeks. None showed signs of abnormal cell growth in the bladder.
Their findings were published this month in the journal Proceedings of the National Academy of Sciences of the United States of America.
The researchers think that nicotine is responsible for the increased risk of cancer in the mice.
They published research last year in the same journal showing that nicotine in human lung and bladder cells can form other chemicals called nitrosamines. These chemicals are potential carcinogens, or cancer-causing agents, in people.
Dr. Margarita Oks, a pulmonologist at Lenox Hill Hospital in New York City, said this study shows that e-cigarettes may also carry some of the same health risks as combustible cigarettes.
“The reason that the vaping industry has been so successful is because of the claim that vaping is safer than smoking cigarettes,” said Oks, who was not involved in the new research. “This study is showing otherwise, albeit in a mouse model.”
While this is a mouse study, and it’s unclear what will happen in humans with long-term e-cigarette use, the devices are so new that researchers will have to wait decades to get a long-term study on humans using e-cigarettes at this point.
Nicotine Suspected in Mice Cancers
Dr. Nima Majlesi, director of toxicology at Staten Island University Hospital in Staten Island, New York, who was not involved in the new study, said it’s difficult to apply the new results to people because potentially carcinogenic chemicals may affect mice and people differently.
But Oks said this research still warrants attention even though it was done in mice.
“All mouse research is done with the purpose of eventually being translated to clinical research as it pertains to humans,” she said.
Majlesi said the new study also raises questions because, “Nicotine itself is not considered a carcinogen. It is the other components in tobacco that cause cancer.”
Nicotine-replacement gums and patches have not been linked to an increased risk of cancer, he said.
The authors of the paper point out that chemicals added during the curing of combustible tobacco are known to cause carcinogenic nitrosamines to form.
Scientists believe that inhaling nitrosamines in tobacco smoke is partially responsible for how cigarettes cause cancer.
However, the 2018 study found that human cells contain chemicals that can react with nicotine to form nitrosamines and other harmful compounds.
The authors point out that more research is needed to determine whether nicotine-containing e-cigarette vapor poses a cancer risk in people, and how frequently someone would need to vape to increase their risk.
Harmful Effects of Vaping
A recent review in The BMJ of previous research shows that vaping has a number of harmful effects in people, even if it isn’t cancer. These effects include respiratory symptoms such as difficulty breathing, increased asthma and bronchitis-like symptoms — especially in adolescents.
Studies also show that vaping can damage lung tissue, increase the risk of bacterial or viral infections in the lungs, and cause the type of lipoid pneumonia seen in some of the recent vaping-related illnesses.
Research has also found that the components of e-liquids — including nicotine, propylene glycol and vegetable glycerin, and flavors — may have negative health effects.
One of the challenges in studying vaping is that e-liquids and e-cigarette devices vary from product to product.
“I am not sure we can re-create all the components of vaping liquid and say that it is universal to all brands,” said Majlesi.
What’s missing from all this research are long-term studies in people on the safety and toxicity of vaping.
Without those, “Saying with certainty that e-cigarettes are safer than combustible cigarettes is impossible,” write the authors of The BMJ review.
Experts Caution Against Vaping
However, there’s enough evidence that vaping isn’t completely safe to raise concerns among health professionals. The recent outbreak of severe lung disease linked to vaping has highlighted how little researchers know about the long term effects of e-cigarettes.
In the outbreak of lung disease linked to vaping, which has sickened over 1,299 and led to 26 deaths, the Centers for Disease Control and Prevention (CDC) believes much of the damage may be from people who were vaping products with THC. But researchers are still investigating.
“Vaping is a major public health issue at this time, and we should discourage vaping of any kind,” said Majlesi. “Although it appears that THC-containing products are most responsible for the recent issues with lung injury.”
Oks said people who currently vape should stop, and those who are considering it should not start.
“There have been so many severe respiratory illnesses — and now deaths — related to vaping that it is not worth the risk,” said Oks, “whether or not this new link to possible cancer is validated in the future.”