The dim light melatonin onset following fixed and free sleep schedules

Aug 27, 2005Journal of sleep research

Timing of Melatonin Increase After Set and Flexible Sleep Schedules

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Abstract

The dim light melatonin onset (DLMO) was more accurately estimated from free sleep times than from fixed sleep times.

In free sleepers, the correlation between DLMO and wake time was r=0.70, compared to r=0.44 in fixed sleepers.
The regression equation predicting the DLMO from wake time in free sleepers was accurate within 1.5 hours in 96% of an independent sample.
Estimating the DLMO may be feasible for individuals with flexible sleep schedules and minimal external sleep disruptions.
Further research is needed to assess DLMO estimation in individuals with more rigid schedules and in populations such as the elderly or those with circadian rhythm disorders.

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The time at which the dim light melatonin onset (DLMO) occurs can be used to ensure the correct timing of light and/or melatonin administration in order to produce desired circadian phase shifts. Sometimes however, measuring the DLMO is not feasible. Here we determined if the DLMO was best estimated from fixed sleep times (based on habitual sleep times) or free (ad libitum) sleep times. Young healthy sleepers on fixed (n=60) or free (n=60) sleep schedules slept at home for 6 days. Sleep times were recorded with sleep logs verified with wrist actigraphy. Half-hourly saliva samples were then collected during a dim light phase assessment and were later assayed to determine the DLMO. We found that the DLMO was more highly correlated with sleep times in the free sleepers than in the fixed sleepers (DLMO versus wake time, r=0.70 and r=0.44, both P<0.05). The regression equation between wake time and the DLMO in the free sleepers predicted the DLMO in an independent sample of free sleepers (n=23) to within 1.5 h of the actual DLMO in 96% of cases. These results indicate that the DLMO can be readily estimated in people whose sleep times are minimally affected by work, class and family commitments. Further work is necessary to determine if the DLMO can be accurately estimated in people with greater work and family responsibilities that affect their sleep times, perhaps by using weekend wake times, and if this method will apply to the elderly and patients with circadian rhythm disorders.

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The dim light melatonin onset following fixed and free sleep schedules

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