When patients’ sleep cycles are out of synch with the rest of the world, melatonin and light therapy can help.

But for night owls – people who fall asleep at 5 a.m. and awake at noon, for instance – it’s important to use a low dose of melatonin, 0.5-1 mg, and it should be given around 7 p.m., 4-5 hours before their desired sleep time, according to Dr. Phyllis Zee, associate director of the Northwestern University Center for Sleep and Circadian Biology in Evanston, Ill.

Bedtime “is not when you give melatonin,” she said. And a small dose is better than a larger one for moving internal sleep clocks forward and less likely to make people sleepy in the early evening.

Night owl patients are clinically described as having a delayed sleep phase disorder, a circadian rhythm problem. Bright light therapy in the early morning, around the time when they would like to wake up, also helps, sometimes in just a few sessions.

Light and melatonin have strong, but opposite, effects on the suprachiasmatic nucleus (SCN), thought to be the brain’s internal clock. Light, especially blue light, increases SCN firing, alerting the body. Melatonin, secreted by the pineal gland under SCN control on a 24-hour cycle, decreases SCN firing, promoting sleep.

Dim light triggers melatonin secretion; endogenous levels begin to rise about 2 hours before sleep, a phenomenon known as dim-light melatonin onset (DLMO). Melatonin supplements help the rise come earlier in night owls, who should also avoid bright light in the evening.

The role of melatonin is uncertain in people with an advanced sleep phase disorder – those who routinely fall asleep at 7 p.m., for instance, and awake at 4 a.m. – but bright light therapy early in the evening can push back their sleep schedule, also in just a few sessions. “In someone with advanced sleep phase, that’s what I would do first. Bright light therapy in the evening,” Dr. Zee said

Patients with circadian sleep disorders don’t have insomnia. Once asleep, they get a full night’s rest.

Even so, being out of synch with the world can cause problems. People with delayed phase disorders can barely get out bed for work, and when they do, they’re sleepy all day. An advanced-phase person’s internal clock tells that person to go to bed when the rest of the world is still active. Such misalignments can trigger actual insomnia and lead to health problems. Delayed phase disorders also correlate with depression.

“Many people who we think have primary insomnia or psychological insomnia actually have delayed or advanced circadian phases. It isn’t so much they complain about insomnia; they really complain about excessive sleepiness,” Dr. Zee said.

To make the right therapeutic call, it’s important to know the timing of patients’ internal clocks. History gives a clue. “I’ve never met a delayed person who is not an owl. I’ve never met an advance sleep phase disorder person who is not a lark,” Dr. Zee said.

A sleep diary helps, too, along with actigraphy, which involves recording wrist activity with a watch-like device worn over several days. It gives a good idea of sleep/wake activity.

DLMO can be accessed directly as well, at least in a sleep lab. In dim light, patients are asked to chew a cotton ball every half hour for 24 hours. Melatonin concentrations are assessed from the saliva. DLMO usually comes at about 9 p.m. for someone on an 11 p.m.-7 a.m. sleep schedule.

Dr. Zee is a consultant for Sanofi-Aventis, Merck, Johnson & Johnson, UCB Pharma, Purdue Pharma, Jazz Pharmaceuticals, and Royal Philips Electronics/Respironics. She also disclosed stock options in Zeo.