|Peter Mansbach PhD, President |
of the Circadian Sleep Disorders
I would like to clarify some things about Circadian Rhythm Sleep Disorders that are often glossed over or not widely recognized.
First and most importantly, there are TWO problems contributing to these disorders. One is that the timing of the body's clock is off. The other is that the sufferer is UNABLE to shift that timing.
Many people are "night owls": their body clocks run late, they want to go to sleep later than is customary in our society, and they get up later in the morning. But many night owls can, with a little attention to proper sleep hygiene, adjust their schedule to be able to work normal daytime hours.
This preference rises to a disorder only when the night owl is UNABLE to adjust their hours without more rigorous treatment. It is called Delayed Sleep Phase Disorder, or DSPD .
What do I mean when I say a person is unable to adjust their sleep hours? I mean that they can set their alarm and force themselves to get up at the desired time, day after day, but when it comes time to sleep, they cannot fall asleep. Their mind becomes active, they toss and turn for hours until their body clock finally decides it's sleep time. By sticking with this schedule they are not getting enough sleep, night after night. They are increasingly tired during the day, find it difficult to function, and this causes long term damage to their bodies. Yet they still do not fall asleep at the desired bedtime.
I've been asked many times to get up early for a doctor's appointment, repairman visit, relative's kid's baseball game, whatever. "Can't you just set an alarm and get up, just this once?" ("Just this once" ... right.) Well, yes I could--but don't try to hold an intelligent conversation with me that early, because I can't even process what you say, let alone formulate an answer, and that's if I don't crash the car on the way there. Once, when I did try to get up really early for an urgent business meeting, I drove onto the highway and found myself facing two lanes of cars coming at me at 60 mph: I had accidentally driven onto an off ramp. Not recommended.
What causes Delayed Sleep Phase Disorder? DSPD refers to a set of symptoms, and there may be different underlying physical abnormalities in different patients. These may include long intrinsic circadian period, lack of sensitivity to light, over-sensitivity to light, deficiencies in the ipRGC cells  of the retina, lack of melatonin production, long elimination time of melatonin, differences in timing of sleep relative to internal circadian rhythms, differences in tolerance to phase mismatch, and possibly others. So it's not necessarily a single disorder with the same cause in all patients.
DSPD is treated using bright light in the morning, avoiding light in the evening, and/or taking melatonin. Timing is critical. Yet not everyone responds well to treatment. Some researchers mentioned a 40 percent success rate, though treatments have improved since then. Why so low? I suspect because different people have different underlying causes, and the researchers tried a one-size-fits-all treatment.
How many people are we talking about? The studies that I'm familiar with estimate the prevalence of DSPD at about 0.15 percent, or 3 in 2000. That's half a million adult Americans! It's also a lot more prevalent in teens, perhaps 7 to 10 percent of them, most of whom will grow out of it.
Regarding Non-24-Hour Sleep-Wake Disorder (Non-24), I want to distinguish between Non-24 in blind people versus in sighted people. The Non-24 diagnosis refers to a set of symptoms in which the patient cannot entrain their schedule to a 24-hour day. Instead, their sleep time progresses later and later each day, going all the way around the clock. It is also called Free Running Disorder.
We know what causes Non-24 in blind people: lack of response to light. People's body clocks do not run at exactly 24 hours. On average, they run about 10 minutes longer than that , but exact timing varies among individuals. The body syncs its clock to the 24-hour day-night cycle through light entering the eyes . In blind subjects, this synchronizing often does not occur .
In sighted people, the causes of Non-24 are believed to be similar to the causes of DSPD. I think we need to view these as two different disorders--Sighted Non-24 and Blind Non-24--since they have such different causes.
I'll close by touching on what I call "the myth of the good night's sleep" in relation to circadian rhythm sleep disorders.
The literature describes DSPD and Non-24 by saying that, if allowed to sleep on their bodies' natural schedules, patients would sleep well and arise fully rested.
For many people this has not been the case. Although they function far better on their own schedule than if they force themselves into a normal sleep schedule, they may still sleep fitfully, or be tired during their wake time.
Thanks to Tamara Sellman at SleepyHeadCENTRAL for this opportunity to post.
 Earlier medical classifications referred to Delayed Sleep Phase Syndrome, DSPS, and this is still a popular term. The current classifications use the term Delayed Sleep Phase Disorder, DSPD.
 ipRGCs: Intrinsically photosensitive retinal ganglion cells. These cells in the eyes are receptive to light even in the absence of the rods and cones in the eye used to "see" light.
 Early studies suggested 25 hours, but that has been discredited. It resulted because the study subjects used light in the evening.
 There was an experiment which claimed light at the back of the knees could entrain the body clock, but that data could not be replicated, so the theory has been abandoned.
 It can still occur, even without visual perception, if the ipRGCs in the retina are unaffected.