The first teenage patient I ever saw as a medical student was 16, thin, had long brown hair, and a long-sleeved flannel shirt. I remember thinking it was strange, when she walked into the clinic, that she would choose to wear something so heavy in the middle of July. When she rolled up her sleeves, I saw why: The scars crisscrossed like roads on a map and extended from her wrists to her upper forearm.
My attending physician at the time, who had plenty of experience with adolescent patients, spoke to her with compassion and allowed her to do most of the talking. The conversation was wide-ranging; among other things, we asked her about her sleep quality, as either sleeping too much or too little can be a symptom of depression. One thing we didn’t ask about, though, was her dreams. We didn’t think the information was relevant.
We may very well have been wrong. Suicide, which claims more than 44,000 lives per year in the U.S., is the second leading cause of death for people between the ages of 15 and 34; meanwhile, up to 23 percent of teens practice self-harm, also known to clinicians as “non-suicidal self-injury” (NSSI). And over the last few months, multiple studies have linked nightmares to an increased risk of both.
There’s no one standard definition for nightmares in the scientific literature, but most researchers generally describe them more or less the same way: “highly dysphoric dreams,” a “disturbing dream that often wakes you up from sleep.” The latest version of the Diagnostic and Statistical Manual, the bible of psychiatric diagnoses, includes an entry for nightmare disorder, defining a nightmare as “an extremely dysphoric and well-remembered dream that usual involves threats to survival, security, or physical integrity.”
Often, when we think of people who struggle with recurring nightmares, we think of people with post-traumatic stress disorder, people who have lived through war or some other harrowing experience. But in one of these recent studies, published in March in the journal Scientific Reports, a team of researchers from the University of Turku in Finland found that frequent nightmares were a risk factor for suicide, even for people without PTSD. The study authors, led by Nils Sandman (who insists his choice to study bad dreams was not influenced by his last name), analyzed data from the Finnish National FINRISK Study between 1972 and 2012, following participants until either 2014 or their death. Even when they excluded all participants who were war veterans, there was a statistically significant overlap between the people who had frequent nightmares (defined as those who answered “often” to the question, “During the past 30 days have you had nightmares?”) and those who ended up committing suicide.
“We found that nightmares can actually be an independent risk factor for completed suicide,” Sandman says, “and it could be an early warning sign that doctors should be asking about.”
Another study, published this month in Comprehensive Psychiatry, found that nightmare frequency can also predict self-harm. Analyzing data from two different samples, one of mental-health patients and one of college students, psychologist Chelsea Ennis and her colleagues from Florida State University found that the association remained, even while controlling for depression symptoms.
“What this suggests is that sleep problems on their own may not lead to self-injury, but it might be that nightmares are related to increased emotional dysregulation, and subsequent higher risk of self-injury,” Ennis says. Her findings echoed those of another recent study of more than 1,000 students in Shandong, China, which found that non-suicidal self-injury was associated with frequent nightmares at double the rate of Ennis’s study.
Not all studies have found this association, though: In 2013, for example, a team of researchers from West Virginia reported that while insomnia was a predictor of suicide risk, nightmare frequency was not. Part of the reason for the inconsistency may be that we still don’t fully understand what nightmares are or what they do. Some researchers have argued that they act as a sort of dress rehearsal for threats we may encounter in waking life, or that they neutralize difficult emotions while we sleep — but just as there’s no one standard definition of a nightmare, there’s no one universally accepted explanation of their purpose. And isolating nightmares alone as a risk factor, without the influence of other issues (such as poor sleep, anxiety, and depression), is a challenge.
While Arshya Vahabzadeh, a psychiatrist at Massachusetts General Hospital, finds the research on nightmares and suicide intriguing, he clarifies that while nightmares may signal the presence of a low or anxious mood, which is associated with suicide risk, simply having nightmares isn’t pathological by default. He also hopes that future studies will be more robust both in how they define a nightmare and how they assess frequency.
“The way that many of these studies [defined nightmares] is somewhat subjective, so future research would need to standardize the definition, in addition to better establishing a cause-and-effect relationship with suicide ideation,” he says.
Vahabzadeh also believes that instead of focusing only on nightmare frequency, physicians could do a better job with asking about sleep disturbances in general, for all patients.
“We know that sleep has a bearing on mood, how we function, and vice versa … it’s bidirectional,” he says. “Most doctors don’t ask enough about sleep when they see a patient with mood concerns, but that’s slowly changing as we become more aware of how important it can affect our mood and general well-being.”
If you or someone you know is experiencing distress, the National Suicide Prevention Lifeline (1-800-273-TALK) and the Crisis Text Line (text HOME to 741741) offer free, confidential support 24/7.
Amitha Kalaichandran, M.D., M.H.S., is a resident physician, epidemiologist, and health/medical journalist based in Canada. Her work has appeared in Stat News, Quartz, Canadian Press, and the Walrus.