There are obvious differences between smoking and vaping, but the more we learn about e-cigarettes, the more we realize that vapers may not have dodged all of smoking’s long-term woes. Smoking and vaping might share emotional consequences that are as bleak as they are mysterious.

Decades of research suggests that smoking has ties to depression. Most recently, a study published this week in PLOS One adds further evidence. In a small sample of 2,000 students from two Serbian universities, scientists found that smokers had higher rates of depression than their non-smoking peers and lower self-estimated mental health overall.

The question is whether or not depressed people are more likely to smoke or if smoking leads to depression. It could be a combination of those ideas. It could also be that nicotine plays a role in the development of poor mental health. What scientists have established is an association between the act and the effect — and they’re continuing to hunt for answers. Especially now, because scientists are starting to see that same link to depression surface among vapers.

Vaping, the proposed “healthier” (still very much out for debate, depending on the country you live in) alternative to smoking, doesn’t appear to have a positive relationship with mental health either.

A JAMA study published in December found that vapers were 1.6 times as likely to be diagnosed with depression compared to people who had never vaped at all. Meanwhile, a survey presented in March 2019 found that vapers were more likely to have a depression diagnosis than non-vapers.

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This connection to depression in both vaping and smoking is unexplained. However, both habits share some attributes that researchers are using to try to explain why both vapor and smoke may affect the brain, as well as the lungs.

The self-medication hypothesis

One leading explanation for the connection between cigarettes and depression is called the “self medication hypothesis.” That’s the idea that, if you’re depressed to start with, you may turn to tobacco as a form of relief. Epidemiologist Hagai Levine, the senior author of the PLOS One paper published Wednesday tells Inverse that this is far from a good solution:

“The tobacco industry tried to manipulate us for many years by creating the wrong impression that smoking makes you feel good,” Levine says. “It’s a complete lie.”

"It’s a complete lie.”

As flawed as attempting to combat depressive symptoms with smoking may be, it could potentially explain why this connection between the condition and the habit exist, says Mohinder Vindyhal, an assistant professor of internal medicine at the University of Kansas School of Medicine. Vindhyal has published research on e-cigarettes and depression in the past

“We believe from the previous tobacco research, patients who are depressed are more likely to use tobacco,” Vindyhal tells Inverse.

From that standpoint, that self-medication may also be the connective tissue between vaping and depression. However, as natural as the connection may seem, Vindhyal cautions that it’s still too early to draw any conclusions.

"Patients who are depressed are more likely to use tobacco.

It could turn out that there is a causal relationship between cigarettes and depression that also applies to vaping.

For traditional cigarettes, there is some research suggesting that smoking may actually lead to depression. For example: a 2019 study published in the journal Psychological Medicine found that smokers were about twice as likely to have depression or schizophrenia. Their statistical analysis also found compelling evidence that smoking could also be fueling those depressive symptoms. The authors write:

“These findings suggest that the association between smoking, schizophrenia, and depression is due, at least in part, to a causal effect of smoking, providing further evidence for the detrimental consequences of smoking on mental health.”

Meanwhile, a study published in 2017 suggests a bi-directional relationship between vaping and depression. That research, conducted on 2,450 teenagers over one year, found that sustained vaping led to an acceleration of depressive symptoms. Those authors also suggested that the relationship between traditional cigarettes and depression may also be present in e-cigarettes.

However, this understanding is still preliminary.

“All we have established is a strong association between e-cigarettes and depression but not causation yet,” Vindhyal says.

The false promise of a nicotine buzz

Although e-cigarettes and cigarettes share a lot of similarities, they’re not perfect substitutes for one another. Vaporizers don’t burn anything, so they don’t release the same harmful chemicals that a lit cigarette does. What they do have in common is nicotine.

JUUL is one of the most popular e-cigarette brands in the US. Shutterstock

One avenue of research has narrowed in on the role of nicotine in the connection between cigarettes and depression, because nicotine can alter the brain’s sensitivity to dopamine, a major component of the brain’s reward system. The JAMA study that specifically investigated e-cigarettes and depression also notes that nicotine’s impact on dopamine could increase sensitivity to stress, or generally mess with the brain’s ability to combat depressive symptoms.

When asked about vaping in the context of his work on cigarettes, Levine also raised the idea that nicotine could have a role to play. In some cases, e-cigarettes deliver more nicotine than traditional cigarettes: One JUUL pod contains the nicotine equivalent of a 20 pack of traditional cigarettes, the CDC estimates.

Levine notes that animal and human studies clearly show that nicotine is harmful to the developing brain, especially when there is quick delivery to the brain, such as by cigarette or e-cigarette.

However, there’s more than just nicotine in a vape cloud. In a previous interview with Inverse, Olufunmilayo Obisesan, the first author of the JAMA study on depression and e-cigarettes and a postdoctoral research fellow at Johns Hopkins Medicine, mentioned that trace metals, like aluminum or lead, are sometimes found in e-cigarettes as well — and may contribute to mental health issues.

Again, the cause for the connection isn’t totally clear. As Levine’s paper notes, there’s no definitive explanation for the connection between cigarettes and poor mental health. Furthermore, vaping research is decades behind tobacco research, making the answer even more elusive.

What can research can prove is that the old idea that quick nicotine buzz can turn a bad mood good is outdated. Levine puts it bluntly: Smoking makes us feel bad, impairs our quality of life, and shortens it. There is a strange connection between choosing to smoke or vape and poor mental health — a connection that researchers hope to understand more fully.