A genotyping study involving tens of thousands of individuals in Finland identified a significant overlap between genetic factors linked to nightmares and those associated with anxiety, depression, posttraumatic stress disorder, and neuroticism. The study also found that individuals with insomnia were more likely to experience frequent nightmares. The research was published in Translational Psychiatry.
Nightmares are vivid and unsettling dreams that typically result in feelings of fear, distress, or anxiety upon awakening. They most often occur during the rapid eye movement (REM) stage of sleep when most dreaming takes place. Nightmares can be triggered by a variety of factors, including stress, anxiety, sleep deprivation, and certain medications or substances. People of all ages occasionally have nightmares. However, frequent and recurrent nightmares can be a symptom of mental health issues.
Scientists believe that nightmares can be caused by fear and negative experiences. For example, traumatic events are clearly associated nightmares in military veterans. Also, studies have shown that people with severe sleep problems, alcohol use or psychiatric symptoms are more prone to nightmares. Still, the risk factors behind nightmares are not well understood.
Study author Hanna M. Ollila and her colleagues wanted to examine the underlying biological and epidemiological mechanisms that affect the frequency of nightmares. They were also interested in discovering causal links between nightmares, sleep, and psychiatric traits. They conducted a genome-wide association study.
A genome-wide association study or GWAS (for short) is a research approach that involves scanning genetic markers across complete genomes of many people to find genetic variations associated with a particular disease or trait. This method allows scientists to identify specific genetic factors that may contribute to the risk of developing a certain condition, by comparing the genetic sequences of individuals with and without the condition.
The data for this analysis were sourced from 45,255 participants involved in several large-scale Finnish studies, including Finrisk, the Finnish Twin Cohort Study, FinHealth, and GeneRISK. Among other data, these studies collected information on the prevalence of nightmares and gathered detailed genetic information about the participants. To eliminate confounding factors, the researchers excluded individuals who reported being intoxicated with alcohol at least once a month from certain analyses.
Results showed that heritability of nightmares based on single-nucleotide polymorphisms (variations among individuals at a single point in a DNA sequence) is relatively small – only 5%. Further analysis revealed that genetic factors associated with frequent nightmares substantially overlap with those associated with posttraumatic stress disorder and a number of other mental health symptoms.
The strongest associations were with the personality trait neuroticism, anxiety, and depression. However, frequent nightmares also showed overlapping genetic factors with insomnia, schizophrenia, and alcohol dependence. Mendelian randomization analysis—a method used to assess causal relationships between risk factors and health outcomes—suggested that insomnia might be a causal risk factor for nightmares, particularly when alcohol use is controlled for.
“These findings show two possible mechanisms for the association of the genetic risk for nightmare with insomnia, either a direct mechanism that is tied to sleep problems and the negativity of a dream or a modulatory effect that is associated with the frequency with which the dream is recalled. Furthermore, heavy alcohol consumption may modify the genetic correlations between nightmares and psychiatric traits,” the study authors concluded.
“Given the significant correlations with psychiatric traits, it would be essential to grow awareness of how nightmares affect health and disease and systematically collect information about nightmares, especially in clinical samples, with a longitudinal follow-up, and then implement these results in larger cohorts.”
The study sheds light on the genetic underpinnings of nightmares. However, it also has limitations that need to be taken into account. Notably, while the genetic data comes from genotyping, data about nightmares were collected using self-reports, with just a single question, leaving room for reporting bias to influence the findings.
The paper, “Nightmares share genetic risk factors with sleep and psychiatric traits,” was authored by Hanna M. Ollila, Nasa Sinnott-Armstrong, Katri Kantojärvi, Martin Broberg, Teemu Palviainen, Samuel Jones, Vili Ripatti, Anita Pandit, Robin Rong, Kati Kristiansson, Nils Sandman, Katja Valli, Christer Hublin, Samuli Ripatti, Elisabeth Widen, Jaakko Kaprio, Richa Saxena, and Tiina Paunio.