b. Menthol

The authors admit this in the paper. They write: "This is a cross-sectional study, which only allows us to identify associations, not causal relationships."

While there is still a lot we do not know about the exact magnitude of any long-term risks associated with electronic cigarette use, vapers should be quite reassured that after at least five years of research into the health effects of vaping, the worst that electronic cigarette opponents can say is: "Well ... they're not harmless."

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