Circadian Rhythm Disorder — Types, Causes, Melatonin & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Circadian rhythm sleep-wake disorders (CRSDs) are conditions where the internal body clock (circadian pacemaker, located in the suprachiasmatic nucleus of the hypothalamus) is misaligned with the environmental light-dark cycle or desired sleep schedule, resulting in impaired sleep initiation, maintenance, or excessive daytime sleepiness. The circadian rhythm is approximately 24 hours and is entrained (synchronised) primarily by light exposure. Major types include: delayed sleep-wake phase disorder (DSWPD — sleep onset after 2-6 am; common in adolescents), advanced sleep-wake phase disorder (ASWPD — very early sleep and awakening; older adults), shift work disorder (SWD), jet lag disorder, irregular sleep-wake rhythm disorder, and non-24-hour sleep-wake rhythm disorder (common in totally blind people). Circadian rhythm disorders affect not just sleep timing but have broad systemic consequences — disruption of the master circadian clock in the suprachiasmatic nucleus affects metabolic function, immune regulation, cardiovascular physiology, hormone secretion, and mental health, making chronobiology an increasingly important field across multiple medical specialties.

DSWPD (most common in teenagers): delayed endogenous circadian phase, partly genetic (mutations in PER3, CLOCK genes); exacerbated by late evening light exposure (smartphones, social media, gaming) suppressing melatonin. ASWPD: age-related advance in circadian phase; genetic (CRY1 mutations). Shift work disorder: working night shifts, rotating shifts, or early morning shifts that conflict with natural circadian rhythm; affects up to 38% of night shift workers. Jet lag: rapid transmeridian travel crossing multiple time zones; eastward travel (advancing the clock) is harder to adapt to than westward travel. Non-24 disorder: absence of light input to the SCN in blind individuals prevents circadian entrainment. Social jet lag: discrepancy between biological sleep need and work/school schedules, particularly in adolescents starting school early.

DSWPD: inability to fall asleep until very late (2-6 am), difficulty waking in the morning, and excessive daytime sleepiness at school/work — but normal sleep duration and quality when allowed to sleep at preferred phase. ASWPD: sleep onset and awakening are both very early (8 pm to 3 am); difficulty staying awake in the evening. Shift work disorder: excessive sleepiness during night shifts, insomnia when trying to sleep during the day, impaired alertness and performance, gastrointestinal upset (disrupted gut circadian rhythm), and mood disturbance. Jet lag: insomnia and daytime sleepiness after long-haul travel, difficulty concentrating, gastrointestinal symptoms, and malaise. All circadian disorders can cause anxiety, depression, and impaired daytime functioning when untreated.

Diagnosis is primarily clinical and chronobiological. Sleep diary (recording sleep timing, quality, and daytime functioning over 1-2 weeks) and actigraphy (wrist-worn activity monitor worn for 1-2 weeks) objectively document sleep-wake patterns and circadian timing. Sleep logs completed daily help identify the sleep phase shift. Melatonin assay: dim-light melatonin onset (DLMO) — the time melatonin begins rising in dim light (blood or saliva collected every 30-60 min from 6 pm) is the gold standard for measuring endogenous circadian phase — delayed beyond 9 pm in DSWPD. Core body temperature minimum is another phase marker. Polysomnography (overnight sleep study) is not required for uncomplicated circadian disorders but excludes comorbid obstructive sleep apnoea or periodic limb movement disorder.

DSWPD treatment: melatonin (0.5-3 mg, taken 5-6 hours before desired sleep time — i.e., 8-9 pm) advances the circadian clock; bright light therapy (10,000 lux bright light box for 30-45 minutes immediately on awakening at target wake time) also advances the phase. Chronotherapy: gradually delaying sleep time by 2-3 hours each day until reaching the target sleep time (used when advancing is difficult). Strict regular sleep-wake schedule — avoiding staying up late at weekends. ASWPD: evening bright light exposure (8-10 pm) delays the phase; avoiding early morning light. Shift work: melatonin before daytime sleep after a night shift; bright light during the first half of the night shift (improves alertness); blackout blinds and sleep masks for daytime sleep. Jet lag: melatonin taken at bedtime at destination — particularly effective for eastward travel; strategic light exposure. Tasimelteon (Hetlioz — melatonin MT1/MT2 receptor agonist) is FDA-approved for non-24 disorder in blind patients.

Untreated circadian rhythm disorders cause chronic sleep deprivation with significant health consequences. Shift work disorder is associated with: increased cardiovascular disease risk (20-40% higher incidence of myocardial infarction), metabolic syndrome and Type 2 diabetes (circadian disruption impairs insulin sensitivity and glucose metabolism), gastrointestinal disorders (peptic ulcer, IBS), breast cancer risk (increased in female night shift workers — classified as probable human carcinogen by IARC), depression and anxiety, and reduced cognitive function and increased workplace accident risk. Adolescents with untreated DSWPD experience chronic sleep deprivation due to early school start times, causing impaired academic performance, mood disorders, obesity, and risk-taking behaviour.

Protect your circadian rhythm: expose yourself to bright natural light (or a 10,000 lux light box) in the morning to entrench the circadian clock to a morning schedule. Avoid bright light exposure (particularly blue-spectrum light from screens) for 1-2 hours before your desired bedtime — use blue-light-blocking glasses or 'night mode' settings on devices in the evening. Keep a consistent sleep-wake schedule 7 days per week — even on weekends. Use blackout curtains for daytime sleep (shift workers) and a sleep mask for travel. If you're a night shift worker: cluster night shifts together rather than alternating with day shifts; rotate shifts forward (day to evening to night) rather than backwards. Strategic napping improves night shift alertness. Schools and employers can mitigate circadian disorder impact by delaying school start times for adolescents and optimising shift scheduling.

See your GP or request a sleep medicine referral if: difficulty falling asleep or waking at required times persists for more than 3 months despite consistent sleep hygiene; the sleep timing problem is causing significant difficulty at work, school, or in daily life; you are excessively sleepy during driving or safety-critical work; or you are a shift worker with persistent insomnia, mood disturbance, or significant health symptoms. Seek GP review if you are a teenager or young adult who consistently cannot fall asleep before 2-3 am even when trying hard — this may be delayed sleep-wake phase disorder (DSWPD), which responds well to timed melatonin and light therapy. Adult-onset circadian disruption with associated symptoms such as loud snoring, witnessed apnoeas, or excessive daytime sleepiness should prompt investigation for obstructive sleep apnoea — which can trigger and worsen circadian rhythm disorders. Blind individuals with non-24-hour sleep-wake rhythm disorder should be referred to a sleep specialist for consideration of tasimelteon (Hetlioz) — an FDA-approved melatonin receptor agonist specifically for this condition.