Have you ever noticed how your mood seems to ebb and flow with the time of day? New research in Sleep Health has shed light on this phenomenon, revealing that our internal biological clock plays a significant role in influencing our mood and overall well-being. The research found that feelings of anxiety and depression peak in the morning hours, while well-being dips, highlighting the intricate link between our circadian rhythm and emotional state.
At the heart of this study is the concept of endogenous circadian rhythms. These are internal processes that follow a roughly 24-hour cycle, regulating various bodily functions, including sleep and metabolism. These rhythms are why we tend to feel sleepy at night and awake during the day, even without external cues like sunlight. Researchers embarked on this investigation to unravel the specific mechanisms through which our circadian rhythm might influence mental health.
“Currently, about 20% of the global population experiences mood and/or anxiety disorders at some point in their lives, which makes it important to understand what specific mechanisms can help explain such risk,” explained study authors Frank A.J.L. Scheer, a professor of medicine at Harvard Medical School, and Sarah L. Chellappa, an associate professor at the University of Southampton.
“Disturbances in sleep and circadian rhythms are bidirectionally intertwined with almost every category of psychiatric disorder. Human studies show day/night (diurnal) rhythms in symptoms of depression and, to some extent, in anxiety symptoms, with a morning worsening and an evening improvement. However, such results come from studies where individuals experience 24-h variations in environmental and behavioral factors, due to for example dark/light, sleep/wake, and rest/activity cycles that may influence their mood.”
“Because of that, we cannot determine the exact role of the endogenous biological (circadian) system to such mood profiles from such studies,” the researchers said. “We, therefore, utilized a stringently controlled circadian laboratory protocol to assess whether the endogenous circadian system modulates depression-like and anxiety-like mood, as well as wellbeing, in young healthy adults.”
To explore these rhythms without the interference of external factors like light exposure or social interactions, Scheer and Chellappa crafted a controlled environment. They enlisted 19 young, healthy adults who underwent a series of assessments to ensure they were free from mood and anxiety disorders.
Over the course of the study, participants followed a fixed sleep schedule before entering a lab setup designed to minimize external cues that could affect their circadian rhythm. They spent two days adapting to this environment, followed by a 32-hour period of continuous wakefulness in dim light, during which they were provided hourly snacks to keep their diet consistent.
The researchers used visual analog scales (VAS) to measure mood perceptions every hour. These scales allowed participants to rate their feelings of anxiety, depression, and overall well-being, including mental fatigue and physical comfort. By analyzing these ratings, the team sought to identify patterns that would reveal the influence of the circadian rhythm on mood and well-being independently of other factors.
Both anxiety-like and depression-like moods exhibited clear circadian patterns, with the highest levels of anxiety and depression recorded during the morning hours, roughly corresponding to 8-9 a.m. Well-being also showed significant circadian rhythms, with the more mental fatigue and less physical comfort occurring in the early morning. These patterns suggest that our internal biological clock directly impacts our emotional state, independent of external influences like sleep or light exposure.
“We were surprised to find out that the circadian system modulates anxiety-like mood levels in a similar way as it does for depression-like mood levels,” the researchers told PsyPost. “We know that sleep and anxiety are interrelated, such that if you experience anxiety during the day – and particularly close to your sleep time – it negatively affects sleep, potentially causing insomnia. Conversely, if one experiences poor sleep quality or insomnia, anxiety levels increase the next day. However, far less is known about whether the circadian system affects anxiety mood. That was a novel finding in our study.”
The study’s findings provide evidence that the worsening of mood and well-being in the morning could be a result of our endogenous circadian rhythms. This aligns with observations in individuals with Major Depressive Disorder, indicating a possible common underlying mechanism. Additionally, the research highlights the circadian system’s role in anxiety-like mood changes, an area previously less understood.
“These results have real-life relevance as they help explain the diurnal rhythm in mood profiles typically occurring in depression and anxiety, for example,” Scheer and Chellappa said. “In other words, they confirm and help explain why the morning hours are likely the time when we experience worse mood and wellbeing. Consistent daily rhythms between individuals with and without depression and/or anxiety suggest these results are relevant to patient populations, although we need future studies to verify this.”
While the study’s controlled setting offers valuable insights into the circadian rhythm’s impact on mood, it’s important to recognize its limitations. The participant pool was relatively homogenous — predominantly young, lean, and White — which may not reflect the broader population.
Future research is poised to build on these findings by exploring circadian rhythms in a wider array of participants, including those with mood and anxiety disorders. Such studies could further elucidate the potential for circadian-based interventions and treatments, offering hope for more personalized approaches to managing mental health.
“Given our study, behavioral interventions that directly target the circadian system, such as light therapy, might help individuals experiencing depression and anxiety,” Scheer and Chellappa explained. “However, we need more research in patient populations to validate such findings, as our study was conducted in young adults without psychiatric disorders.”
The study was titled: “Endogenous circadian rhythms in mood and well-being.”
