Original ArticleDaytime sleepiness during transition into daylight saving time in adolescents: Are owls higher at risk?
Introduction
Daylight saving time (DST) is used to balance the seasonal-caused daylight exposure changes to the activity peaks of a given population, and it affects millions of people [1]. Therefore, it is necessary to investigate the impact of DST because it affects the diurnal or circadian rhythm, and different chronotypes may respond differently towards DST [1], [2], [3], [4], [5], [6]. Individuals differ in their circadian preference and in their circadian clocks; therefore, DST may affect the diurnal rhythm and may lead to abnormalities such as sleep problems [3]. DST adds to the chronic sleep loss [7] as is seen, e.g., in the increase of accidents after DST in spring [8]. Further, sleep reduction is supposed to trigger the appearance of mental illness; DST may also have an influence on the appearance [9]. Disturbances of the sleep–wake cycle are associated with numerical clinical symptoms such as seasonal affective disorder or bipolar disorder [9], [10], [11], [12], [13]. With respect to chronotype, depressed patients are often more shifted towards eveningness, suggesting a link between mental health and morningness [11], [12].
These individual differences in biological rhythms or in circadian typology are viewed as an interesting facet of personality [14]. In general, “larks,” or morning types, prefer to get up and go to bed early, while “owls” prefer later bed times and later rise times [15], [16], [17], [18], [19]. Usually, such an assessment of individual difference in chronotype is based on self-reporting [18], [19] and these differences in morningness–eveningness (chronotype) can be considered on a continuous scale [20].
The variability in the circadian clock is heritable and some genes have been identified that are associated with morningness–eveningness [21], [22], [23]. Above and beyond the genetic influence which is roughly estimated to account for about 50% of the variance in circadian typology [23], social, cultural and environmental factors modulate the circadian preference [24], [25], [26], [27].
Chronotype changes significantly during the lifespan. While younger children are often morning larks, adolescents shift considerably towards eveningness during puberty [28], [29], [30], [31], [32], [33] and back towards morningness at the end of adolescence [33]. During later years of adulthood, aged people turn far more towards morning activity [34]. Results concerning gender differences were inconclusive [34], but in larger samples morningness was higher in girls or women [35], [36]. Morningness–eveningness has been found to correlate with some of Eysenck’s personality dimensions [37], [38] or with the conscientiousness scale of the Big Five Personality Inventory [39] or Millon Personality Styles [40].
The change in diurnal preference in adolescence has severe consequences on lifestyle and school functioning [41], [42], and the turn towards eveningness is associated with depressive tendencies [43], poor performance at non-optimal times of day [16], behavioural difficulties [43], [44] and higher familial and social demands [45].
Given these studies, one may expect that adolescents may suffer most from a transition into DST because during the transition in spring time, clocks are typically adjusted forward one hour. The transition into daylight saving has rarely been the focus of research, especially because it is argued that a shift of one hour should be easily coped with (comparably to a jetlag). Studies about DST were carried out by Monk and Folkard [4] and Monk and Aplin [5]. These authors found that adjustment of times of retiring and falling asleep appeared to be instantaneous, while it took up to a week to adjust wake-up times. The results of Berk, Dodd, Hallam, Gleeson and Henry [6] showed that suicide rates in males rise in the weeks following the commencement of daylight saving. Kantermann et al. [2] further suggest that humans do not adapt to DST, while Lahti et al. [3] emphasise that evening types have more problems in adapting to DST, and morning types experience the shift back as more problematic.
We hypothesise that adolescents scoring high on morningness should more easily adapt to DST, especially in adolescence.
Section snippets
Participants and data collection
Data were collected from girls and boys in Germany during the transition into daylight saving time in spring 2008. Participation was voluntary, unpaid and anonymous. Informed consent was obtained from pupils, their parents and the principals of the schools. Four hundred and sixty-nine teenagers participated in this part of the study. There were 251 girls and 218 boys. The mean age was 13.5 years (SD = 2.2, range 10–20 years). Participants were recruited from three schools. All students attended
Results
Daytime sleepiness and eveningness both correlated with age, suggesting that daytime sleepiness and eveningness increase with age (PDSS: pre: r = 0.267, p < 0.001; post: r = 0.315, p < 0.001; CSM: r = −0.226, p < 0.001). The CSM scores and both measures of daytime sleepiness were also correlated (prior: r = −0.623, p < 0.001, N = 432, Fig. 1; post: r = −0.565, p < 0.001, N = 384) suggesting that evening types report higher daytime sleepiness.
Daytime sleepiness was higher after the transition into daylight saving time
Discussion
The data on daytime sleepiness suggest there is a general trend over the total sample for a higher sleepiness after transition into DST until approximately the third week after. However, these data only showed a trend to significance. This may have several reasons, e.g., the instrument PDSS may not be sensitive enough to discover differences, but this seems unlikely since it was specially developed to measure these differences [46]. Further, the general trend for the total sample may be weak
Acknowledgements
We highly appreciate the collaboration of the schools, principals, teachers and especially pupils which made the study possible. Two anonymous reviewers provided helpful comments that improved the structure and presentation of the initial manuscript.
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