Researchers found that people who use electronic cigarettes had substances in their urine that have been linked to bladder cancer.

In the study in the journal European Urology Oncology, researchers compiled the results of 22 different studies that analyzed the urine of people who used e-cigarettes or other tobacco products, including cigarettes, to check for evidence of cancer-linked compounds or biomarkers of those compounds. They found six biomarkers or compounds with a strong link to bladder cancer.

“Smoking is the No.1 modifiable behavioral risk factor for bladder cancer,” said UNC Lineberger’s Marc Bjurlin, DO, MSc, associate professor of urology in the UNC School of Medicine. “There is now evolving literature showing that people who vape may have similar carcinogens in their urine as combustible cigarette users.”

While public health agencies including the US Food and Drug Administration and the Centers for Disease Control and Prevention have warned that there are health risks of vaping, including for e-cigarette-associated lung injury, their safety profile has not been “definitively characterized,” according to Bjurlin and his colleagues.

“The first and foremost side effects that we’re seeing from electronic cigarette use are lung and pulmonary related,” Bjurlin said. “We won’t see the side effects for these other kinds of carcinogenic pathways until much later down the exposure pipeline.”

To develop a better understanding of the long-term risks of vaping, including cancer, researchers investigated possible exposure to substances that can cause bladder cancer in particular since carcinogens could be processed in the body and then passed in urine.

In their review, Bjurlin and his colleagues found 40 different parent compounds that can be processed in the body to produce 63 different toxic chemicals or carcinogenic metabolites, which are substances that remain after in the body after processing.

Six of those chemicals have a strong link to bladder cancer, according to researchers’ analysis of carcinogens databases of the International Agency for Research on Cancer and the Collaborative on Health and the Environment Toxicant and Disease Database.

They found evidence in some studies that e-cigarette users had “significantly” higher levels of several carcinogens that can be metabolized into substances linked to bladder cancer in their urine compared to people who had never used them.