Introduction

• Morning-type individuals show a preference for going to bed and waking up early, and accomplish the peak of their mental and physical performance in the early part of the day

• Evening type individuals achieve their peak towards the end of the day and consequently prefer later bed and wake up times

• Most people fall along the middle part of the continuum

• Circadian preference can influence physical and mental health, in terms of well-being, but also sickness and disease

Chronotype and Mood Disorders

Depression

• Eveningness appears to be an independent risk factor for both subclinical depressive symptoms and onset of a depressive disorder among young people

• Among adults, eveningness has been associated with an increased likelihood of reporting depressive symptomatology, increased symptom severity, and being diagnosed with a de- pressive disorder

• Among depressed individuals, evening types tend to exhibit worse symptom severity and report increased psychological distress, higher suicidality and more impairment in their daily lives, and more symptoms of anxiety

• Eveningness does not appear to be associated with either suicidal ideation or attempt among individuals without a psychiatric diagnosis Eveningness has been associated with a lower behavioral activation system, which in turn leads to lower reward responsiveness and lower positive affect, and consequently depressive symptoms

• Evening-type individuals experience worse mood in the mornings

• Evening types have been shown to have impaired emotion regulation, higher self-blame and reduced positive reappraisal

• Increased rumination levels in evening types

• Social jetlag: misalignment between the internal clock and the social clock

Bipolar Disorder

• Bipolar patients are more likely to be evening types

Seasonal Affective Disorder

• Evening-type adolescents have been found to report higher mood seasonality

• Individuals with seasonal affective disorder are also more likely to have an evening preference throughout the year

Chronotype and Anxiety Disorders

• Eveningness has been associated with trait anxiety in female adolescents

• Eveningness was not associated with anxiety disorders among adolescents after sleep complaints were controlled for

• Evening-type firefighters and military veterans showed increased PTSD symptoms compared to other chronotypes

Chronotype and Psychotic Disorders

• The association between chronotype and psychotic disorders does not point to a straightforward link

Chronotype and Addictive Disorders

• The evening chronotype is considered a major risk factor for substance use among young people

• The evening chronotype has also recently been associated with compulsive internet use among young adults

• Eveningness has been associated with a personality type characterized by greater impulsivity, disinhibition, and sensation seeking

Chronotype and Sleep Disorders

• Shift towards eveningness starts at roughly 13 years of age and peaks at age 20

• Evening-type adolescents report more irregular sleep-wake cycles, poorer subjective sleep quality, and more daytime sleepiness, also resulting in more napping

• Delayed sleep phase syndrome has also been associated with eveningness in adolescence and may result in chronic fatigue, low mood, and academic difficulties

• Evening-type adults include decreased subjective sleep quality, insufficient sleep, excessive daytime sleepiness, and trouble initiating sleep

Chronotype and Eating Behaviour/Disorders

• Morning-type individuals tend to exhibit healthier and more regular eating habits and higher control over their eating

• Evening types tend to be less physically active and report poorer perceived health