Assessment of biological components associated with sleepiness in young working college students

Objectives: An association, responsible for affecting circadian rhythms and sleep homeostasis, between PER3 gene variable number tandem repeat (VNTR) and sleep times has been described in humans. The aim of this study was to evaluate the association between clock genes VNTR and sleep duration, chronotype and melatonin secretion. Methods: A hundred forty-six students filled a questionnaire about their sleep habits to determine individual preferences. Salivary samples were also collected for DNA extraction. PER3 VNTR was genotyped using PCR. Results: Seventy subjects were PER3 4/4 (47.9%), 61 PER3 4/5 (41.8%) and 15 PER3 5/5 (10.3%). Mean sleep duration of PER3 5/5, intermediate chronotype students (8h) was higher than PER3 4/4, morningness chronotype (5:58h). On days-off, for evening-types, sleep outset was delayed (10:44h) when compared to morning-types (09:38h). Part of the students took part in a study about bright light intervention and its effects upon sleepiness. When exposed to bright light at 19:00h, the students’ sleepiness growth went as expected. But, when exposed at 21:00h, sleepiness slightly increased for the intermediates and decreased at 22:00h for the evening-type students. Analyzing PER3 and HIOMT genotypes a specific haplotype, associated to melatonin levels at 19:00h and after bright light exposure, at 19:20h, was detected. Conclusion: With no social restrictions for sleep onset/outset, chronotypes express different sleep preferences, partly associated to PER3 VNTR genotype.