Longitudinal data show cause-effect connection between sleep problems and depression and anxiety

According to authors Nguyen et al., their recently published study was the first to examine whether having poorer overall subjective sleep quality plays a role in the link between Generalized Anxiety Disorder (GAD) and Major Depressive Disorder (MDD) severity across 18 years. The authors prefaced their study by noting that as much as one fifth of the world’s population suffers from anxiety or depression, and that more research is needed to understand why people with MDD also tend to have GAD over a long period of time. Other researchers in this arena generally used cross-sectional studies, preventing any causal inferences to be made. So, Nguyen et al. conducted a secondary analysis of publicly available longitudinal data from over 3,000 adults who participated in three measurement waves of Midlife in the United States (MIDUS), each nine years apart, spanning 18 years: MIDUS 1, 1995-1996; MIDUS 2, 2004-2006; and MIDUS 3, 2013-2014. MIDUS, which is distributed via the National Archive of Computerized Data on Aging, was the first national, longitudinal study of aging to focus explicitly on midlife, and it was one of the first national studies to link psychosocial and behavioral factors to biomedical and neurological assessments obtained in laboratory settings. Nguyen et al. hoped to get a cause-effect understanding of the bi-directional relations between sleep problems and depression and anxiety, especially since MIDUS included a thorough psychiatric diagnostic interview, unlike many previous studies that relied on scales with “limited clinical diagnostic criteria.” The authors also were able to create a measure of global sleep quality, because during MIDUS 2, the Pittsburgh Sleep Quality Index (PSQI) was administered, and it contained different facets of the sleep experience.

There were 3,294 MIDUS participants in the authors’ analytical sample of adults who had consented to complete in-person clinical interviews to determine their MDD and GAD diagnostic status, and had completed the PSQI in the second wave. Using measures of MDD, GAD, and sleep quality, and after controlling for multiple sociodemographic and clinical variables, Nguyen et al. found that MIDUS participants with higher levels of anxiety and depression at the beginning of the study had lower sleep quality nine years later. Lower sleep quality at the second wave then predicted higher levels of anxiety and depression nine years after that. They also found that poor sleep quality explained 41 percent of the relationship between anxiety and later depression, and 11 percent of the relationship between depression and later anxiety. Collectively, the authors noted, their results were in line with the transdiagnostic theory of sleep, which suggests that long-term sleep problems can cause damage to biological systems in the body, leading to the bidirectional relationship between poor sleep quality and depression and anxiety symptoms over time.