Effects of Chronotype and Sleep Timing Behavior on Mental Health

Lok, R., Weed, L., Winer, J., & Zeitzer, J. M. (2024). Perils of the nighttime: impact of behavioral timing and preference on mental health in 73,888 community-dwelling adults. Psychiatry Research, 337, 115956.

Rationale

Mental health is independently influenced by both chronotype (the inclination to sleep at specific times) and actual sleep timing (behavior). However, chronotype and actual sleep timing are often misaligned.

Previous research has shown associations between evening preference and mental health disorders (Díaz-Morales & Sánchez-Lopez, 2008; Konttinen et al., 2014; Lemoine et al., 2013), particularly in individuals with depression (Chan et al., 2014).

However, the impact of the alignment between chronotype and actual sleep timing on mental health has not been thoroughly investigated in a large-scale study.

The next step in this field of research was to examine how chronotype, sleep timing, and the alignment between the two impact mental health in a large community-dwelling cohort. This study aimed to fill this gap by analyzing data from 73,888 middle- and older-aged adults in the UK Biobank.

Method

The study utilized data from the UK Biobank, a large community-dwelling cohort of middle-aged and older adults.

Participants wore wrist-worn triaxial accelerometers for seven consecutive days to determine their behavioral timing. Chronotype was assessed through a questionnaire.

Mental health disorders were identified using ICD-10 codes. The study examined the impact of chronotype, behavioral timing, and the alignment between the two on mental, behavioral, and neurodevelopmental disorders (MBN), depression, and generalized anxiety disorder (GAD).

Procedure

Participants wore accelerometers for seven consecutive days, 24 hours per day.

They also completed questionnaires providing information on demographics, health status, and lifestyle. Chronotype was determined based on a single question about morning or evening preference.

The timing of behavior was determined by analyzing accelerometry data to identify the five consecutive hours with the lowest activity levels (L5). Mental health disorders were assessed using ICD-10 codes from medical records.

Sample

The final sample included 73,888 participants from the UK Biobank. The sample was 56% female, with a median age of 63.5 years.

The median Body Mass Index was 26.0, and the median Townsend Deprivation Index was -2.45. The majority (97.1%) of the sample was self-reported to be Caucasian.

Measures

• Chronotype: Assessed through a single question, categorizing participants as morning-type, intermediate-type, or evening-type.
• Timing of behavior: Determined using accelerometry data, categorized as early, intermediate, or late based on the start time of the least active 5-hour period (L5).
• Mental health disorders: Identified using ICD-10 codes for Mental, Behavioral, and Neurodevelopmental disorders (MBN), depression, and Generalized Anxiety Disorder (GAD).
• Sleep duration: Self-reported in hours.
• Interdaily Stability: Calculated as a non-parametric measure of sleep-wake stability.

Statistical measures

The study used chi-square tests to examine the frequency of disorder diagnosis. Generalized linear models were used to determine the likelihood of having a disorder. Survival analyses (Cox proportional hazards analysis) were conducted to determine differences in disease-free intervals.

All analyses were adjusted for demographic factors, self-reported sleep duration, and sleep-wake stability. Statistical significance was corrected for multiple tests using a Bonferroni correction.

Results

The study did not explicitly state hypotheses, but the main results include:

• Evening chronotype was associated with a higher prevalence and increased likelihood of MBN, depression, and GAD compared to intermediate chronotype.
• Late timing of behavior was associated with a higher prevalence and increased likelihood of MBN, depression, and GAD compared to intermediate timing.
• Misalignment between chronotype and timing of behavior was associated with higher frequencies of MBN and depression, with a trend for GAD.
• Morning-types with late behavior had an increased risk of MBN, depression, and GAD compared to aligned morning-types.
• Evening-types with early behavior had a decreased risk of depression compared to aligned evening-types, with trends for decreased risk of MBN and GAD.
• Longitudinal analyses confirmed that evening chronotype and late timing of behavior were associated with increased likelihood of developing de novo mental health disorders.

Insight

The key finding of this study is that for all chronotypes, having an earlier sleep schedule is better for mental health. This is particularly informative because it challenges the common belief that aligning sleep patterns with one’s preferred sleep time (chronotype) is always best for mental health.

The study extends previous research by examining not just chronotype or sleep timing separately, but also the alignment between the two. It provides evidence that the actual timing of sleep may be more important for mental health than matching one’s chronotype.

These findings suggest that the timing of sleep, independent of sleep duration or chronotype, plays a crucial role in mental health. This opens up new avenues for research into the mechanisms underlying this relationship.

For example, future studies could investigate how late-night wakefulness affects decision-making processes or alters prefrontal cortex functioning, potentially leading to mood disturbances.

The next steps in the field could include:

1. Investigating the neurobiological mechanisms underlying the relationship between late sleep timing and mental health disorders.
2. Exploring interventions that aim to shift sleep timing earlier, regardless of chronotype, and assessing their impact on mental health outcomes.
3. Examining how societal factors (e.g., work schedules, social norms) interact with individual sleep timing preferences to affect mental health.
4. Strengths:

Strengths

• Large sample size (73,888 participants), providing robust statistical power.
• Use of objective measures (accelerometry) to assess behavioral timing, rather than relying solely on self-report.
• Consideration of both cross-sectional and longitudinal data, allowing for analysis of both current associations and future risk.
• Adjustment for multiple confounding factors, including sleep duration and sleep-wake stability.
• Use of standardized ICD-10 codes for mental health disorder diagnosis, ensuring consistency in disorder classification.

Limitations

• The study relied on self-reported sleep duration, which may not accurately reflect actual sleep time.
• Mental health disorders were identified using ICD-10 codes, which may not capture all individuals with a given disorder and could be subject to inter-physician variation.
• Chronotype was assessed using a single question, which may not provide as comprehensive an assessment as more extensive questionnaires.
• The sample was predominantly Caucasian, potentially limiting the generalizability of findings to other racial or ethnic groups.
• The relatively young cohort and short interval between initial assessment and follow-up limited the sample size for longitudinal analyses.

These limitations may affect the precision of sleep duration estimates, the accuracy of mental health disorder prevalence, and the generalizability of findings to more diverse populations. The short follow-up period may have underestimated the long-term impact of sleep timing on mental health.

Implications

The results of this study have significant implications for research, clinical practice, and public policy. The finding that going to sleep before 1 AM, regardless of chronotype, is associated with better mental health outcomes provides a clear, actionable message for public health initiatives.

For clinical practice, these results underscore the importance of considering sleep timing, not just sleep duration, when assessing and treating mental health disorders. Clinicians may need to pay more attention to patients’ sleep schedules and consider interventions that aim to shift sleep timing earlier, even for patients who identify as “night owls.”

In terms of research, these findings highlight the need for more studies investigating the mechanisms underlying the relationship between late sleep timing and mental health. This could lead to new targets for intervention in mental health disorders.

From a public policy perspective, these results could inform discussions about work schedules, school start times, and other societal factors that influence sleep timing. Policies that promote earlier sleep times could potentially have significant public health benefits.

The study also suggests that the relationship between sleep timing and mental health is influenced by factors beyond just chronotype and sleep duration. This emphasizes the complexity of sleep’s role in mental health and the need for comprehensive approaches in both research and clinical practice.

References

Primary reference

Lok, R., Weed, L., Winer, J., & Zeitzer, J. M. (2024). Perils of the nighttime: impact of behavioral timing and preference on mental health in 73,888 community-dwelling adults. Psychiatry Research, 337, 115956.

Other references

Chan, J.W.Y., Lam, S.P., Li, S.X., Yu, M.W.M., Chan, N.Y., Zhang, J., & Wing, Y.-K. (2014). Eveningness and insomnia: independent risk factors of nonremission in major depressive disorder. Sleep, 37(5), 911-917.

Díaz-Morales, J.F., & Sánchez-Lopez, M.P. (2008). Morningness-eveningness and anxiety among adults: a matter of sex/gender? Personality and Individual Differences, 44(6), 1391-1401.

Konttinen, H., Kronholm, E., Partonen, T., Kanerva, N., Männistö, S., & Haukkala, A. (2014). Morningness–eveningness, depressive symptoms, and emotional eating: a population-based study. Chronobiology International, 31(4), 554-563.

Lemoine, P., Zawieja, P., & Ohayon, M.M. (2013). Associations between morningness/eveningness and psychopathology: an epidemiological survey in three in-patient psychiatric clinics. Journal of Psychiatric Research, 47(8), 1095-1098.

Keep Learning

Socratic questions for a college class to discuss this paper:

1. How might societal norms and work schedules interact with individual chronotypes to affect mental health outcomes?
2. What potential mechanisms could explain why later sleep timing is associated with poorer mental health outcomes, regardless of chronotype?
3. How might the findings of this study inform public health policies related to work and school schedules?
4. What ethical considerations should be taken into account when developing interventions to shift individuals’ sleep timing earlier?
5. How might the relationship between sleep timing and mental health vary across different cultures or in societies with different sleep norms?
6. Given the limitations of this study, what additional research would be necessary to more definitively establish the relationship between sleep timing and mental health?
7. How might these findings impact our understanding of the relationship between circadian rhythms and mental health disorders?
8. What are the potential implications of these findings for the treatment of insomnia and other sleep disorders?