Sleep patterns in Portugal: European and International comparisons

Sleep represents an essential element for health and well-being, including cognitive performance, physiological processes, emotional regulation, physical development, and quality of life and is the best observed circadian rhythm in humans. Humans show large differences in the preferred timing of their sleep and activity, so-called chronotypes. Ranging from extreme early types to extreme late chronotypes, the majority falls between these extremes. While chronotype and sleep necessity appear to be independent characteristics, the difference in sleep duration between workdays and work-free days is nonetheless chronotype-dependent because of our social schedules. Extremely earlier chronotype experience shorter sleep duration on free-days and longer on workdays. On the other hand, the later chronotypes have shorter sleep duration on workdays and longer on free days. Its described in literature that chronotypes become later from eastern to western border of time zones. The social time is equal, whereas solar time is progressively delayed, producing a later phase of entrainment and increased discrepancies between individuals' social and biological circadian times, that can lead to a higher circadian disruption with potential health detriments. Portugal is in Greenwich Meridian Time (GMT) time zone, the second most western and the most southern country, so it is expected that the Portuguese might be especially late chronotypes. Therefore, to explore their sleep/chronotype is of major interest.The studies present in this thesis aimed to characterize the sleep/wake phases of the Portuguese general population as well as in sleep medicine patients and to compare them with other countries/samples. The characterization of a clinical sample of extreme late chronotypes and to evaluate how much the social clocks influence the sleep quality in sleep disorder patients were also objectives of this thesis. In order to accomplish these objectives five different studies were performed: Study 1) Aiming to evaluate self-reported average sleep duration (n= 5,436 adults; EpiDoC3 cohort) and its possible associations with demographic features and chronic medical disorders. Cross-sectional, populational based study. The prevalence for Short Sleep Duration (SSD) was high (20.7%) and for Long Sleep Duration (LSD) (5.9%) was relatively low. Being older, with lower education, retired and unemployed were associated to SSD and LSD (p<0.01). Being obese was associated to SSD as well as hypertension, gastrointestinal disease and hypercholesterolemia (p<0.01). SSD and LSD, were associated with diabetes (p<0.01 and p=0.03, respectively) and with depression (p<0.01 and p=0.02, respectively). Cardiovascular disease (p<0.01) was associated to LSD. Multimorbidity was associated to SSD (p<0.01). Worse quality of life and bad physical function were associated to SSD and LSD, as well as being hospitalized in the previous 12 months (p<0.01). Study 2) Aimed at understanding if the reported “usual” sleep quality assessed by the Pittsburg Sleep Quality Index (PSQI) reflects workdays sleep of sleep disorder patients and to find a social influence on sleep quality detriment of these patients. Cross-sectional, case-control study. 431 sleep disorder patients and 338 subjects from the general population answered three variants of the PSQI (usual (u), work (w), work-free (f) days) and the Munich Chronotype Questionnaire (MCTQ). PSQI scores differed between groups (p<0.001). Post-hoc analysis revealed a significant difference between PSQIu vs. PSQIf and PSQIw vs. PSQIf with PSQIf presenting lower scores, while PSQIu vs. PSQIw did not differ in any group. In line with previous findings, Social Jetlag (SJL) was associated to PSQIdiff in sleep disorder patients. Study 3) Aimed at validating the Portuguese variant of the MCTQ. Cross-sectional observational study, including the, 80 Portuguese individuals from the general population with 4 weeks of actimetry and MCTQ; The median mid-point of sleep, chronotype (MSFsc) was 4:33 (abs range: 2:04 – 8:45). The 1st quartile was earlier than 3:43, and the 4th quartile later than 5:15. Extreme chronotypes (2.5% at each end of the distribution) were earlier than 2:20 and later than 8:36. Comparing the average chronotype of Portuguese subjects with other countries, the Korean’s were the latest (MSFsc = 5:07) followed by the Portuguese (MSFsc = 4:37), the German (MSFsc = 4:22) and the Japanese (MSFsc = 4:18). For the extreme late chronotypes the Portuguese (8:36) was later than the late 2.5% in the Korean sample (8:34). High correlations between MCTQPT and actimetry derived data were found showing that the MCTQ was a reliable questionnaire to access sleep timings and phase of entrainment for the Portuguese adult population. Study 4) Aimed at characterizing a clinical population of delayed sleep-wake phase disorder (DSWPD) patients. In 5 years of registries 245 patients with DSWPD were identified and 162 patients had performed at least one objective sleep/wake/phase measure (actimetry, DLMO, PSG). Gender differences for the different age groups (p=0.028) were observed. Men were more likely to be single and women more likely to be married (p=0.034). In students, school failure was higher for women (p<0.001); for workers, absenteeism was higher in women (p=0.001). In the circadian aligned (compared to misaligned group), DLMO was later (p<0.001), sleep onset time (p=0.046) was later, total sleep time (p=0.035), and number of sleep cycles (p=0.018) were lower, as measured using PSG T1. Study 5) Aimed at comparing 9 European countries in relation to chronotype, average sleep duration and social jetlag. Cross-sectional observational study. 164,234 individuals from the MCTQ-database (8 countries) and a sample of Icelanders (total n=165,378). The average chronotype among the studied countries ranged between 3.97  1.16 for Belgium and 5.15  0.25 for Spain, for the Central European Greenwich Meridian Time zone (GMT+1) and between 4.21  1.41 for the United Kingdom and 4.76  1.46 for Portugal among the GMT countries. The average Sleep Duration ranged between 7.36  0.21 for Spain and 7.67  0.95 for Belgium, for the GMT+1 and between 7.33  1.05 for Ireland and 8.12  2.42 for Portugal, among the GMT countries. The average SJL ranged between 1.32  0.92 for Netherland and 1.65  0.16, for Spain for the GMT+1 and between 1.24  0.93 for United Kingdom and 1.70  0.86 for Iceland among the GMT countries.In conclusion, the work in this dissertation showed the associations to self-reported total sleep time and chronic diseases and poor health quality to the Portuguese population. A negative social influence on reported sleep quality of Portuguese sleep disorder patients was present. Social jetlag was a predictor for poor sleep quality, mediated by chronotype. We suggest that treatment strategies addressing social aspects affecting sleep quality on workdays and minimizing actions for circadian strain would be of major importance on sleep medicine clinical practice. Late type seems to be common among the Portuguese and this was shown not only for subjective data as well as by objective data. Recommendations is something that needs to be considered in our society since it can cause a circadian misalignment, when leaving against our biological clocks. The causes of circadian misalignment and health detriments were well shown in this thesis and have an economic impact measured by the absenteeism and hospitalizations of the EpiReuma study, which should more precisely evaluated in future studies. Sleep education and awareness campaigns are needed for Portugal (general population, physicians, employers and policy makers) in order to advertise to this lateness predisposition, find countermeasures strategies and advertise for health consequences of leaving against the clock.