Sleep and circadian phase characteristics of adolescent and young adult males in a naturalistic summertime condition

Our aim was to compare the circadian phase characteristics of healthy adole scent and young adult males in a naturalistic summertime condition. A total of 19 adolescents (mean age 15.7 years) and 18 young adults (mean age 24.5 years) with no sleep problems took part in this study. Two-night polysomno graphic (PSG) sleep recordings and 24h secretion patterns of urinary 6-sulf atoxymelatonin were monitored in all 37 subjects. Sleep-wake patterns were initially assessed at home using a standard sleep diary. Circadian assessme nt included the measure of dim light melatonin offset (DLMOff) and the morn ingness-eveningness (M/E) questionnaire. As expected, compared to young adu lts, adolescents habitually spent more nocturnal time in bed and spent more time (and percentage) in delta sleep. No difference was found between adol escents and young adults on multiple sleep latency test (MSLT) sleep onset latencies, M/E, melatonin secretion measures (24h total, nighttime, daytime , and night ratio), and DLMOff. For the subjects as a whole, correlational analyses revealed a significant association between the DLMOff and M/E and between both these phase markers and habitual bedtimes, habitual rising tim es, and melatonin secretion measures (daytime levels and the night ratio). No association was found between phase markers and daytime sleepiness or sl eep consolidation parameters such as sleep efficiency or number of microaro usals. These results together indicate that adolescents and young adults in vestigated during summertime showed similar circadian phase characteristics , and that, in these age groups, an evening phase preference is associated with a delayed melatonin secretion pattern and delayed habitual sleep patte rns without a decrease in sleep consolidation or vigilance.