Sometimes I hear from people whose trouble sleeping sounds more like a circadian rhythm disorder than insomnia. Here’s what Laurel wrote:
I have trouble sleeping virtually every night—it is not intermittent—and I always have. I was a poor sleeper as a child, staying up until very late (3 a.m. to 5 a.m.), then being exhausted during the next school day and napping in the afternoon . . . continuing the vicious cycle. This pattern has pretty much stayed the same throughout my adult life. It seems to run in the family, as my mother had awful insomnia, as does my sister.
Laurel was taking sleeping pills to get to sleep at night. But if her problem has mainly to do with her body clock—if what she has is delayed sleep phase disorder (DSPD)—she’d be better off with other types of treatment.
Symptoms of DSPD
DSPD symptoms are similar to the symptoms of people with sleep onset insomnia:
- Trouble falling asleep at bedtime
- Catastrophic thinking at night (related to how their inability to fall asleep will affect their performance or interpersonal functioning the next day)
- Poor cognitive functioning in the daytime and irritable mood
But in one fundamental way, the symptoms associated with the two disorders are different. Sleep onset insomniacs are inclined to poor sleep regardless of sleep opportunity. People with DSPD, in contrast, can generally get a good night’s sleep when allowed to sleep during the hours of their choosing (as, for example, when they’re on vacation). Their sleep problem has mainly to do with timing. School and work obligations fit poorly with their internal circadian rhythms. The result is sleep loss, poor performance, and, over time, reduced life prospects.
It begins in adolescence. Then, for unknown reasons, children experience a biological delay in their sleep pattern. This delay causes them to want to go to bed and get up later (which is why later school start times for middle and high school students makes so much sense).
Then, as people reach the age of 20 or so, most of us start shifting backward again to earlier preferred bed and wake times. But a small number of people don’t shift back. They become night owls, and their preference to stay up till 3 and in bed till 11 can persist into middle age and beyond.
Delayed Circadian Rhythms
What keeps people like Laurel running late? Two phase markers determine when we feel like sleeping and when we’re ready to wake up. Onset of melatonin secretion is one. Melatonin secretion is negligible during the daytime but high at night, starting about 1 to 2 hours before normal bedtime. Research has shown that melatonin secretion begins about 4 hours later in people with DSPD than in normal sleepers.
The second phase marker is core body temperature. We’re physiologically alert at times when our core body temperature is high and sleepy when it’s low. Normal sleepers’ body temperature is highest—and physiological alertness, greatest—in the evening from about 6 to 9 p.m. In people with DSPD, this temperature high occurs 2 to 6 hours later.
The lowest core body temperature in normal sleepers—when people are sleepiest— occurs around 5 a.m. Research has shown that the body temperature low occurs on average over 2 hours later in people with DSPD. No wonder they can sleep right through buzzing alarm clocks.
A Longer Circadian Period
Studies have also shown that people with DSPD have longer-than-normal circadian periods. The average circadian period in humans—the time it takes to complete a full cycle—is 24 hours 12 minutes. Exposure to sunlight corrects for the 12-minute delay and keeps most of us running on 24-hour days.
The body clock in people with DSPD tends to run slow, cycling once every 25 or even 26 hours. The 1- or 2-hour advance needed to bring them into sync with the 24-hour day is harder to accomplish, say sleep experts, and likely another cause of DSPD.
The gold standard in treatment for people with DSPD is early morning bright light therapy combined with a melatonin supplement taken around dinnertime:
- Bright light: The light source can be the sun or a light box that disseminates light at 10,000 lux. Light exposure should occur immediately upon waking up. Two-hour sessions are most effective.
- Melatonin supplement: Phase advances are also larger when morning bright light therapy is combined with a melatonin supplement taken late in the afternoon or early in the evening. In a recent study, 0.5 mg of melatonin taken late in the afternoon and 30 minutes of bright light therapy in the morning produced 75% of the phase shift that occurred with the 2-hour light exposure.