The latest study on e-cigarettes has found that the flavoring liquid used in them may increase the risk of cardiovascular disease when inhaled. And, among six different popular flavors that were tested— cinnamon, menthol, fruit, tobacco, sweet tobacco with caramel and vanilla, and sweet butterscotch—cinnamon and menthol were found to be particularly harmful.

For the study, scientists from Stanford University School of Medicine investigated the effect of the e-liquids on cells, called endothelial cells, that line the interior of blood vessels. They found that, when grown in a laboratory, endothelial cells exposed to the e-liquids — or to blood collected from e-cigarette users shortly after vaping — are less viable (fewer healthy cells) and increase the amount of molecules that cause damage to the DNA. The cells are also less able to form new vascular tubes (that help in transporting fluids) and participate in wound healing.

“Until now, we had no data about how these e-liquids affect human endothelial cells,” said Joseph Wu, MD, PhD, director of the Stanford Cardiovascular Institute and professor of cardiovascular medicine and of radiology, in a statement. “When we exposed the cells to six different flavors of e-liquid with varying levels of nicotine, we saw significant damage. The cells were less viable in culture, and they began to exhibit multiple symptoms of dysfunction,” he added.

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The researchers also said that the severity of the damage, aspects of which occur even in the absence of nicotine, varies among popular flavors.

As mentioned above, besides cinnamon and menthol that were found to be the most harmful, caramel and vanilla also disrupted growth, but not as severely.

This study comes at a time when various toxicology studies have hailed e-cigarettes as a safer option for smokers compared to conventional cigarettes. Scientists have said they carry not more than 5% of the risk of combustible cigarettes.

Last month, India’s first-ever study on the Electronic Nicotine Delivery System or ENDS, said that they pose a lower health risk and could be an ideal tool to reduce or give up smoking. Among its key findings, the experts concluded that chemicals such as carcinogens and other toxicants were found in significantly higher quantities in conventional cigarette smoke as compared to the vapour from an e-cigarette.

Now, it’s for India’s 100 million adult smokers to decide which part of the story to believe, although Wu says that, “This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes.”