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Scientists discover one sleep habit is most likely to result in happiness

Your body clock may predict important mental health outcomes.

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Night owls may have a certain cool factor — glowing eyes, mesmerizing hoots, and killer instincts — but chipper morning larks actually have it better. At least, they do in the human world: Research suggests people who naturally wake up early are often able to avoid serious mental health challenges while enjoying a work schedule that aligns more closely with their natural clocks.

A study published Monday in Molecular Psychiatry provides further compelling evidence that morning people are at an advantage. Researchers looked at genetic data from over 450,000 people, compared it with their sleep habits, and found those predisposed to late sleep schedules were also experiencing more clinical depression.

How the discovery was made — To find a pattern between genes, misaligned sleep, and mental health, researchers had to crunch the numbers on an enormous sample of data.

This data was pulled from 451,025 people whose information is stored in the UK Biobank, a biomedical database. These adults are between 40 and 70-years-old and live across England, Scotland, and Wales.

The study team examined whether or not the participants' DNA contained specific variants associated with diurnal preference — a tendency toward “morningness” or “eveningness” — and asked them when they enjoyed waking up.

Beyond variants, it’s previously been shown that a certain profile of genetic information actually dictates much of our “natural” sleep schedule — known as our “chronotype” — so researchers looked at subgroups of participants, examining for a “genome-wide significance.” These participants kept track of their daytime and nighttime activities and filled out mental health questionnaires. When possible, the study team also incorporated information on participant’s work schedules.

Sleep, the body clock, and mood

The researchers found a number of ways that our internal clocks interact with our waking lives.

  • Genetically categorized morning people and those who preferred waking early had lower odds of expressing markers of clinical depression compared to evening people.
  • Genetically categorized morning people and those who said they preferred waking early also reported greater well-being on questionnaires.
  • Morning people appeared to have less “behavioral circadian misalignment” (a measure the researchers used to capture inconsistency in sleep schedules throughout the week and on average).
  • More of this circadian misalignment was strongly associated with more anxiety, depression, and worse well-being.
  • Shift workers, typically people who work hours outside of 7 a.m. and 6 p.m, showed similar outcomes — more depressive symptoms with more misalignment. In this case, even being a morning person didn’t seem to protect them.

The more “morningness” a person had, the less likely they were to have mental health outcomes like major depression.

Molecular Psychiatry / O'Loughlin, et al.

Why it matters — It’s been known for some time that night-owl habits are linked to anxiety and depression. Previous studies have found being prone to early rising can predict better well-being, and that being forced to wake up early for work as a night-owl can lead to lower brain connectivity and performance.

Some past studies, the authors note, have even observed “social jetlag” — the sleep pattern disruption from staying up later on the weekends and earlier on weekdays — as the link between sleep times and mental well being.

This large-scale study is some of the strongest evidence yet that our internal sleep clock actually affects our happiness — and not just the other way around.

In this case, using genetics to determine who might be more prone to “morningness” or “eveningness” and then looking at their mental health is a step in establishing a cause-effect relationship between the two. Their measure of sleep misalignment also paints, seemingly, a more complete picture of inconsistent sleep timing.

What’s next — Researchers say that while their study, which used genetic data, provides evidence of a causal effect, they can’t completely rule out a chicken-and-egg scenario. Does poor sleep follow the development of depression or vice versa? More research is needed to know for sure.

The “misalignment” measure this study used to describe how aligned our sleep schedule is with our natural sleep tendencies could also be used as starting point in future studies. It’s possible, the study team reasons, misalignment may be the missing link between our sleep preferences (night owl, morning person) and mental health.

This measurement is also useful because it describes sleep inconsistency over time through a comparison of sleep midpoints, rather than just how early or late someone gets up. But more studies are needed to refine descriptions of this relationship between misaligned sleep schedules and well-being.

How this can be used — With more information about the relationship between the sleep schedule our body wants and the one it gets, we’re one step closer to alleviating symptoms of depression by adjusting sleep schedules, or even adjusting work schedules to match our circadian rhythms.

We already know more sleep is better for mental health, but studies like this one reinforce a more strategic approach, where one might at least try being more consistent with a sleep schedule. Another recent study suggests simply moving the midpoint of sleep back an hour by going to sleep one hour earlier (and waking up at the same time as usual) could in itself decrease depression symptoms.

Workers can try to adjust sleep to work schedules, but on the other side of the coin, work could adjust to them. It’s hard to envision a world where your boss sets a personalized schedule based on your natural diurnal rhythms — but if the recent mass rejection of traditional beliefs on work-from-home schedules are anything to go by, we might not be as far away from optimal sleep alignment as we think.

Abstract: Late diurnal preference has been linked to poorer mental health outcomes, but the understanding of the causal role of diurnal preference on mental health and wellbeing is currently limited. Late diurnal preference is often associated with circadian misalignment (a mismatch between the timing of the endogenous circadian system and behavioural rhythms), so that evening people live more frequently against their internal clock. This study aims to quantify the causal contribution of diurnal preference on mental health outcomes, including anxiety, depression and general wellbeing and test the hypothesis that more misaligned individuals have poorer mental health and wellbeing using an actigraphy-based measure of circadian misalignment. Multiple Mendelian Randomisation (MR) approaches were used to test causal pathways between diurnal preference and seven well-validated mental health and wellbeing outcomes in up to 451,025 individuals. In addition, observational analyses tested the association between a novel, objective measure of behavioural misalignment (Composite Phase Deviation, CPD) and seven mental health and wellbeing outcomes. Using genetic instruments identified in the largest GWAS for diurnal preference, we provide robust evidence that early diurnal preference is protective for depression and improves wellbeing. For example, using one-sample MR, a twofold higher genetic liability of morningness was associated with lower odds of depressive symptoms (OR: 0.92, 95% CI: 0.88, 0.97). It is possible that behavioural factors including circadian misalignment may contribute in the chronotype depression relationship, but further work is needed to confirm these findings.

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