Circadian rhythm

• Why are biological clocks important? Our cyclical environment:

  • light-dark cycle
  • food availability
  • temperature
• Circadian rhythms are endogenous - not driven by the light-dark cycle
• Some people's sleep-wake cycles don't fit a daytime schedule and cannot be changed simply by discipline. Forcing people with circadian rhythm sleep disorders to live according to society's schedule often results in sleep deprivation and may lead to chronic illnesses such as fibromyalgia, diabetes, heart disease and cancer.
• Circadian rhythm sleep disorders are physiological. Faulty rhythms of melatonin, cortisol and core body temperature can be measured.
• Delayed Sleep-Wake Phase Disorder - people who sleep and wake very late. Most common circadian rhythm disorder. Affects 1 in 600 adults. About 10% of teenagers develop temporary DSWPD.
• Non-24 hour sleep-wake disorder - people who have more than 24 hours in their sleep-wake cycle whihc moves right around the clock over several weeks. Both blind and sighted people can have non-24.
• Advanced sleep-wake phase disorder - people who sleep and wake very early.
• Misdiagnosis of circadian rhythm sleep disorders is common. CRSDs can look like depression, ADHD, primary insomnia and other disorders.
• Treatments for CRSD

  • good sleep hygiene not sufficient
  • sleeping pills not an effective long term treatment
  • morning bright light exposure
  • evening light reduction
  • melatonin
  • when treatments don't work, home life suffers and formal accomodations are needed at work and/or school
  • currently no cures
• Clock alterations

  • causes
  • social jet lag
  • shift work
  • jet lag
  • leads to
  • health problems
  • industrial accidents, road accidents
• Social Jetlag

  • chronic sleep loss
  • misalignment of biological and social time
  • linked with health problems
• Specific Diurnal Rhythm Conditions

  • jet lag
  • shift work disorder
  • social jet lag
  • advanced sleep wake phase disorder
  • delayed sleep wake phase disorder
  • non 24 hour sleep wake disorder
• Jet Lag

  • body's internal clock has been disturbed from long air travel time to a destination that is two or more time zones different from your home
  • this sleep-wake cycle disruption makes it difficult to adjust and function in the new time zone
  • eastward travel is more difficult than westward travel because it is easier to delay sleep than to advance sleep
• Common features of jet lag

  • change in appetite
  • changes in gastrointestinal (stomach and bowel) function
  • general tiredness, drowsiness during the day
  • general feeling of discomfort or uneasiness and mood disturbance
  • difficulty falling asleep (insomnia)
  • headaches
  • lack of focus and concentration
  • general feeling of being off
  • mood changes, irritability
• How is jet lag treated?

  Get some sun

  Adjust sleep-wake schedule

  Focus on getting quality sleep

  Avoid new foods

  Drink lots of water
• Shift work sleep disorder

  • frequently rotating shifts or working at night
  • work schedules conflict with body's natural circadian rhythm, making it difficult to adjust to change
  • identified by constant or recurrent pattern of sleep interruption that results in insomnia or excessive sleepiness
• common features of sleep disorder

  • ongoing tiredness
  • general feeling of discomfort or uneasiness, mood disorde
  • gastrointestinal problems
  • decreased libido
  • other health risks include increased risk of alcohol and substance abuse, weight gain, high blood pressure, heart disease and breast and endometrial cancer
• Management of shift work sleep disorder

  • get 7-9 hours of sleep every day
  • make sleep a priority
  • prepare for sleep even in daylight
  • minimise exposure to light on the way home from night shift to keep morning sunlight from activating normal internal daytime clock
  • follow bedtime rituals and keep regular sleep schedule, even on weekends and days off from work
  • quiet, dark and peaceful setting during sleep time
  • ask family to keep noise down
• Bright light therapy

  • increases night-time sleep
  • higher daytime activity
  • lower daytime sleep
• Melatonin

  • increases sleep time
  • decreases nocturnal activity
  • no change in daytime sleep
• Persistent disrupted circadian rhythms possibly linked with other conditions

  • affective disorders (bipolar depression)
  • sleep disorders
  • neurodegenerative disease (e.g. Alzheimer's)
  • obesity/metabolic syndrome
  • inflammation (asthma, COPD)
  • cancer
• Melatonin

  • increases night-time sleep
  • higher daytime activity
  • lower daytime sleep
  • increases sleep time
  • decreases nocturnal activity
  • no change in daytime sleep