“Resetting the Late Timing of ‘Night Owls’ Has a Positive Impact on Mental Health and Performance”, 2019-08 ():
In this study, we took a [n = 22; 12 vs 10] group of ‘night owls’ (ie. people with extreme late sleeping and waking patterns) and attempted to shift their habitual late timings earlier in a real-world setting using simple, practical non-pharmacological interventions. Using this intervention we can:
Achieve a phase advance of around 2 h
Decrease self-reported ratings of depression and stress
Reduce sleepiness in the morning
statistically-significantly improve simple indices of cognitive and physical performance
Background: There is conflict between living according to our endogenous biological rhythms and our external environment, with disruptions resulting in negative consequences to health and performance. This is often documented in shift work and jet lag, but ‘societal norms’ (eg. typical working hours) can create profound issues for ‘night owls’, people whose internal biological timing predisposes them to follow an unusually late sleep-wake cycle. Night owls have also been associated with health issues, mood disturbances, poorer performance and increased mortality rates.
Method: This study used a randomized control trial design aimed to shift the late timing of night owls to an earlier time (phase advance), using non-pharmacological, practical interventions in a real-world setting. These interventions targeted light exposure (through earlier wake up/sleep times), fixed meals times, caffeine intake and exercise.
Table 1: Details of intervention schedule given to participants in the experimental group. The control group were given a single instruction (shown in bold). Method of monitoring adherence (in addition to a feedback questionnaire administered post-intervention) is given for each intervention target. Intervention target Instructions given How adherence was monitored Wake up time Participants were asked to try and wake up 2–3h before habitual wake up time. · Participants were asked to maximize outdoor light exposure during the mornings. Continuous monitoring pre/post-intervention through actigraphy and sleep diaries. Sleep/wake timings Participants were asked to try and keep sleep/wake times fixed (within 15–30 min) between workdays and free days. Continuous monitoring pre/post-intervention through actigraphy and sleep diaries. Sleep onset Participants were asked to try and go to sleep 2–3h before habitual bedtime. · Participants were asked to limit light exposure during the evenings. Continuous monitoring pre/post-intervention through actigraphy and sleep diaries. Diet/nutrition Participants were asked to keep a regular schedule for daily meals. · Participants were asked to have breakfast as soon after wake up as possible. · Participants were asked to eat lunch at the same time every day. · Participants were asked not to have dinner after 19:00 h. An online questionnaire was completed at all testing sessions to record time since last meal. Caffeine intake Participants were asked not to drink any caffeine after 15:00 h. An online questionnaire was completed at all testing sessions to record time since caffeine intake. Power naps Participants were asked not to nap after 16:00 h. Napping was recorded through self-reported daily sleep diaries. Exercise If exercise was part of an individual’s usual routine they were asked to schedule this during the morning. An online questionnaire was completed at all testing sessions to record time since exercise. Results: Overall, participants demonstrated a statistically-significant advance of ~2 h in sleep/wake timings as measured by actigraphy and circadian phase markers (dim light melatonin onset and peak time of the cortisol awakening response), whilst having no adverse effect on sleep duration. Notably, the phase advance was accompanied by statistically-significant improvements to self-reported depression and stress, as well as improved cognitive (reaction time) and physical (grip strength) performance measures during the typical ‘suboptimal’ morning hours.
Conclusions: Our findings propose a novel strategy for shifting clock timing towards a pattern that is more aligned to societal demands that could statistically-significantly improve elements of performance, mental health and sleep timing in the real world.
[Keywords: chronotype, circadian phase markers, non-pharmacological interventions, depression, stress, performance]