Home Circadian Phase Assessments with Measures of Compliance Yield Accurate Dim Light Melatonin Onsets

Abstract

Study objectives: There is a need for the accurate assessment of circadian phase outside of the clinic/laboratory, particularly with the gold standard dim light melatonin onset (DLMO). We tested a novel kit designed to assist in saliva sampling at home for later determination of the DLMO. The home kit includes objective measures of compliance to the requirements for dim light and half-hourly saliva sampling.

Design: Participants were randomized to one of two 10-day protocols. Each protocol consisted of two back-to-back home and laboratory phase assessments in counterbalanced order, separated by a 5-day break.

Setting: Laboratory or participants' homes.

Participants: Thirty-five healthy adults, age 21-62 y.

Interventions: N/A.

Measurements and results: Most participants received at least one 30-sec epoch of light > 50 lux during the home phase assessments (average light intensity 4.5 lux), but on average for < 9 min of the required 8.5 h. Most participants collected every saliva sample within 5 min of the scheduled time. Ninety-two percent of home DLMOs were not affected by light > 50 lux or sampling errors. There was no significant difference between the home and laboratory DLMOs (P > 0.05); on average the home DLMOs occurred 9.6 min before the laboratory DLMOs. The home DLMOs were highly correlated with the laboratory DLMOs (r = 0.91, P < 0.001).

Conclusions: Participants were reasonably compliant to the home phase assessment procedures. The good agreement between the home and laboratory dim light melatonin onsets (DLMOs) demonstrates that including objective measures of light exposure and sample timing during home saliva sampling can lead to accurate home DLMOs.

Clinical trial registration: Circadian Phase Assessments at Home, http://clinicaltrials.gov/show/NCT01487252, NCT01487252.

Keywords: circadian; compliance; light; melatonin.

Figure 1

Sample protocols for a subject who typically slept from 23:00 to 07:00. Participants were randomized to Protocol A or Protocol B. Protocol A consisted of a home phase assessment, a laboratory phase assessment, a 5-day break, a laboratory phase assessment, and a home phase assessment. Protocol B consisted of a laboratory phase assessment, a home phase assessment, a 5-day break, a home phase assessment and a laboratory phase assessment. The gray rectangles represent the time required for dim light. The dot represents the time of the first saliva sample, with saliva sampling continuing every 30 min up until 2 h after average bedtime. The black rectangles represent scheduled sleep times. Square brackets indicate approximate arrival and departure times from the laboratory.

Figure 2

The clock time of dim light melatonin onsets (DLMOs) collected in laboratory phase assessments versus home phase assessments. The two measures were highly correlated (r = 0.91, P < 0.001). The line is the line of unity.

Figure 3

Individual melatonin profiles collected in a home phase assessment either the day before or day after a laboratory phase assessment. Top panel: An example of when the home dim light melatonin onset (DLMO) occurred before the laboratory DLMO. Middle panel: An example of when the home DLMO occurred at the same time as the laboratory DLMO. Bottom panel: An example of when the home DLMO occurred after the laboratory DLMO.

Figure 4

The distribution of the difference between the laboratory dim light melatonin onsets (DLMOs) and home DLMOs, calculated by subtracting each home DLMO from its corresponding laboratory DLMO. The zero line represents no difference between the DLMOs, a positive difference reflects the home DLMO occurring earlier in time than the corresponding laboratory DLMO, while a negative difference reflects the home DLMO occurring after the corresponding laboratory DLMO. The solid lines represent the mean differences in each protocol. The dashed lines represent a 30-min difference and a 1-h difference between the home and laboratory DLMOs.