Circadian rhythm disorders are fairly common, affecting approximately 20% of the population. Yet it is one of the areas often overlooked in naturopathic education and one that’s going to show up in your primary care office.
Here are a few faces of circadian rhythm disorders you may have seen: the shift worker who has hypertension or digestive disorders (about 20% of Americans do shift work of some type), the teenager who can’t sleep until 2am yet has to get up at 6am for school, and the business professional who travels regularly for work and says it’s getting harder and harder.
Here is a brief overview of this category of disorders, and some of the treatment principles.
Circadian disorders occur either when there is disorder in the circadian timekeeping system, the entrainment mechanisms, or when the endogenous rhythm is out of sync with social norms such as school / work hours. The central pacemaker cells are located in the SCN (suprachiasmic nucleus) which cues the pineal gland to release melatonin in the absence of light (hence the name “the hormone of darkness”). Peripheral timekeepers are the clock genes in every cell. The primary way that our clock is entrained to the environment is by the first daily exposure to bright light.
According to The International Classification of Sleep Disorders, 3rd Edition, 2014, here are the circadian rhythm sleep-wake disorders briefly summarized:
- Delayed Sleep-Wake Phase Disorder. The body clock is set later than norms, making it difficult to fall asleep at the time necessary to get sufficient sleep before morning commitments. Note that about 10% of people with chronic insomnia are thought to actually have delayed sleep-wake phase disorder.
- Advanced Sleep-Wake Phase Disorder. The body clock is set earlier than norms, making it difficult to stay up to a normal bedtime, and causing the person to wake very early. Years ago I had a 9 year old patient who would fall asleep at 5p, and wake naturally by 4a, which caused social problems in the afternoon, and family disruption in the early morning.
- Irregular Sleep-Wake Rhythm Disorder. The sleep periods are of various lengths, and erratically timed.
- Non-24-Hour Sleep-Wake Rhythm Disorder. This is common in the blind, and characterized by a standard main sleep period that regularly moves either later or earlier each day.
- Shift Work Disorder. A disturbed sleep and wake pattern associated with shift work which results in impairment.
- Jet Lag Disorder. Travel across two or more time zones can cause insomnia, excessive daytime sleepiness and wake time impairment.
- Not otherwise specified
Each of these disorders causes problems with excessive daytime sleepiness, or insomnia, or commonly both. The person will also be impaired in other domains such as mental, physical, or social functioning, or have difficulties in their occupational or educational setting.
The main treatment for these disorders in most cases is precisely timed bright light therapy in accordance with the Phase Response Curve (PRC). The PRC is a chart that demonstrates whether light will have a phase advancing or phase delaying effect when given at a particular time relative to the patients main sleep period. In a nut shell, bright light before the main sleep period will delay the body clock, while bright light at the end of the sleep period will push it earlier (ie advance it). Low dose melatonin can also be given as an adjunct, although it does not have as powerful an effect.
As a clinician, I encourage you to consider circadian rhythm disorders when you are working with patients who are on erratic schedules, or who have complaints of excessive daytime sleepiness or even fatigue.