Circadian rhythm is the body's natural, internal process that regulates physical and mental functioning with a cycle of about 24 hours. It is controlled by a pacemaker in the brain and influences sleep-wake cycles, temperature, and hormone regulation. Circadian rhythm disorders occur when the body's internal clock is misaligned with external demands, causing insomnia or excessive sleepiness. Jet lag results from travel across time zones disrupting circadian rhythms, while shift work misaligns circadian rhythms from working during normal sleep periods, increasing health risks. Treatments include light therapy, drugs to improve sleep, and optimizing sleep schedules.

1. CIRCADIAN RHYTHM

2. WHAT IS CIRCADIAN RHYTHM
• The term circadian was coined by FRANZ HALBERG.
• It comes from two Latin words: Circa means around and Diem/Dies means a day. And thus Circadian
Rhythm means that last around 24 hours (one day).
• Circadian Rhythm is any biological process that displays an endogenous (built in), entrainable (can be
adjusted according to various external environment) oscillation of about 24 hrs. it is 24 hrs biological
rhythm controlled by a pacemaker in brain that sends messages to other systems in the body.
• It influences various regulatory functions like sleep wake cycle, body temperature regulation, pattern
of activity such as eating and drinking, hormonal and neurotransmitters secretions, etc.
• Endogenous pacemakers are internal body clocks that keeps biological processes to time.
• Exogenous zeitgebers are external cues that entrain internal body clock, i.e; altering body clock to
match external environment.

3. CIRCADIAN RHYTHM DISORDER.
• The sleep-wake cycle is under the circadian control of oscillators and can be disrupted by
misalignment between an individual’s biologic clock and external demands on the sleep
cycle. Circadian rhythm sleep disorders usually present with either insomnia or
hypersomnia.
• Aetiology :
1. Intrinsic factors: delayed sleep phase syndrome, advanced sleep phase syndrome,
irregular sleep wake pattern.
2. Extrinsic factors: shift work, jet lag, etc.

4. JET LAG.
• Jet lag occurs when a person travels across time zones, and the external environmental time
is mismatched with the internal circadian clock. Sleep disturbances typically last for 2 to 3
days, but can last as long as 7 to 10 days if the time zone changes are greater than 8 hours.
• Jet lag leads to increased incidence of gastrointestinal disturbances and a decrease in
alertness and performance.
• Treatment of jet lag includes non pharmacologic approaches alone or in combination with
drug therapy. Short-acting benzodiazepine receptor agonists or 0.5 to 5 mg melatonin taken
at appropriate target bedtimes reduces jet lags

6. SHIFT WORK
• Night shift work causes a misalignment in the sleep-wake cycle and circadian rhythm that is associated
with a decrease in alertness, performance, and quality of daytime sleep.
• Shift workers ultimately are at risk of developing shift work sleep disorder (SWSD). SWSD is a complaint
of insomnia or excessive sleepiness that occurs because of working shifts during normal sleep time.
• Shift workers have a higher injury rate, rate of divorce, occurrence of on-the-job sleepiness, and
incidence of substance use. Shift workers can also be at increased risk of developing peptic ulcers, heart
disease, depression, breast cancer, and sleepiness related accidents.
• Treatment for shift work sleep problems includes optimizing sleep hygiene, extending daytime sleep by
sleeping in the afternoon, scheduling a 2- to 3-hour nap on days off from work, or switching to a day
shift job. Short-acting benzodiazepine receptor agonists can consolidate sleep during day sleep periods
and reduce lost sleep time
• Modafinil is FDA approved to improve wakefulness in patients with excessive daytime sleepiness
associated with SWSD.
• Scheduled exposure to bright lights at night and darkness in the daytime improves adaptation to night
work and daytime sleep.