Individual differences in the amount and timing of salivary melatonin secretion

Abstract

The aim of this study was to examine individual differences in a large sample of complete melatonin profiles not suppressed by light and search for possible associations between the amount and timing of melatonin secretion and a multitude of lifestyle variables. The melatonin profiles were derived from saliva samples collected every 30 minutes in dim light from 85 healthy women and 85 healthy men aged 18-45 years. There was a large individual variability in the amount of melatonin secreted with peak values ranging from 2 to 84 pg/ml. The onset of melatonin secretion ranged from 18:13 to 00:26 hours. The use of hormonal birth control, reduced levels of employment, a smaller number of days on a fixed sleep schedule, increased day length and lower weight were associated with an increased amplitude of melatonin secretion. The use of hormonal birth control, contact lenses, a younger age, and lower ratings of mania and paranoia were associated with a longer duration of melatonin secretion. An earlier occurrence of the onset of melatonin secretion was associated with an earlier wake time, more morningness and the absence of a bed partner. Lifestyle and behavioral variables were only able to explain about 15% of the individual variability in the amount of melatonin secretion, which is likely because of a substantial genetic influence on the levels of melatonin secretion.

Figure 1. Six individual melatonin profiles determined from half hourly saliva samples collected in dim light.

Shown are two melatonin profiles with the lowest AUC (A, B), two melatonin profiles with low AUC but normally shaped melatonin profiles (C, D), and two melatonin profiles with the highest AUC (E, F). The profiles are plotted with reference to assigned bedtime. The peak value of each profile is shown above the corresponding point on the profile. The threshold used to determine the DLMO and DLMOff is represented by the horizontal line. The DLMO and DLMOff are indicated by arrows.

Figure 2. The frequency distributions of peak value, area under the curve, time of the DLMO and melatonin duration (DLMO-DLMOff).

The frequency distributions of peak value and area under the curve were positively skewed, while DLMO and DLMO-DLMOff were normally distributed.

Figure 3. The mean melatonin profiles of females using (“BC”, n = 16) or not using hormonal birth control (“no BC”, n = 69) and males (n = 85).

The profiles are plotted with reference to assigned bedtime. Error bars represent SEMs.

Figure 4. The mean melatonin profiles of the unemployed (n = 35), students and/or part-time workers (n = 116) and full-time workers (n = 19).

The profiles are plotted with reference to assigned bedtime. Error bars represent SEMs.