A reader asks:

 What is delayed sleep phase disorder (DSPD)?


DSPD is a circadian rhythm disorder in which the internal body clock is synchronized abnormally late with respect to local clock time, making it virtually impossible to fall asleep at a conventional hour (say, between 10 p.m. and 12 midnight vs. 3-5 a.m.). In some cases, this is a lifetime disorder, caused by a genetic predisposition, and it can run in families. In other cases, a person slips into delayed phase by purposely staying up unusually late and sleeping in a darkened bedroom without early morning bright light exposure. Sleeping pills do not solve the problem. Careful use of bright light therapy can be effective.

Delays, but not Extreme

For those without extreme delayed phase (say, with sleep onset between 1-2 a.m.), a good strategy is to estimate current circadian rhythm phase using the Automated Morningness-Eveningness Questionnaire at www.cet.org. The results will show a time in late morning when light exposure should be used to begin resetting the internal clock. Every few days, the treatment can be moved earlier (say, in 30 minute steps) until sleep onset normalizes.

Extreme Delays

The Questionnaire is not designed for those with extreme delayed phase, however. In such cases, light therapy should start around the time of spontaneous waking (say, 1 p.m.), and stepped earlier as described above. Successful application of these methods, taking into account individual differences, may require supervision by a specialist. In some cases, it is appropriate to take a low dose of melatonin 12 hours before the scheduled light therapy, for a synergistic effect.