Robust stability of melatonin circadian phase, sleep metrics, and chronotype across months in young adults living in real-world settings.

Appropriate synchronization of the timing of behaviors with the circadian clock and adequate sleep are both important for almost every physiological process. The timing of the circadian clock relative to social (ie, local) clock time and the timing of sleep can vary greatly among individuals. Whether the timing of these processes is stable within an individual is not well-understood. We examined the stability of circadian-controlled melatonin timing, sleep timing, and their interaction across ~ 100 days in 15 students at a single university. At three time points ~ 35-days apart, circadian timing was determined from the dim-light melatonin onset (DLMO). Sleep behaviors (timing and duration) and chronotype (ie, mid-sleep time on free days corrected for sleep loss on school/work days) were determined via actigraphy and analyzed in ~ 1-month bins. Melatonin timing was stable, with an almost perfect relationship strength as determined via intraclass correlation coefficients ([ICC]=0.85); average DLMO timing across all participants only changed from the first month by 21 minutes in month 2 and 5 minutes in month 3. Sleep behaviors also demonstrated high stability, with ICC relationship strengths ranging from substantial to almost perfect (ICCs = 0.65-0.85). Average DLMO was significantly associated with average chronotype (r2  = 0.53, P <.01), with chronotype displaying substantial stability across months (ICC = 0.61). These findings of a robust stability in melatonin timing and sleep behaviors in young adults living in real-world settings holds promise for a better understanding of the reliability of previous cross-sectional reports and for the future individualized strategies to combat circadian-associated disease and impaired safety (ie, "chronomedicine").

Qualidade do sono e cronotipo de estudantes de enfermagem / Sleep quality and chronotype of nursing students

Resumo Objetivo Verificar a qualidade do sono, o cronotipo e as características de saúde associadas à qualidade de sono de estudantes. Métodos Estudo descritivo observacional e transversal com 204 estudantes do curso de graduação em enfermagem (faixa etária de 18 à 29 anos; 91,6% sexo feminino). Foi utilizado um questionário para caracterização sociodemográfica e de saúde. O questionário de Índice de Qualidade de Sono de Pittsburgh e o Questionário de Identificação de Indivíduos Matutinos e Vespertinos foram aplicados para a verificação da qualidade do sono e a identificação do cronotipo respectivamente. Foram analisadas a associação entre as variáveis de saúde e a qualidade do sono. Resultados A maioria dos estudantes foi identificada com preferência de cronotipo indiferente (56,37%) e com qualidade de sono ruim (84,31%). Houve associação entre ser estudante e trabalhar com os sintomas de má digestão, cefaleia, sonolência diurna e insônia. Conclusão Estudantes de enfermagem possuem qualidade de sono ruim e preferência de cronotipo indiferente; aqueles que, acumulam as funções estudo/trabalho, apresentam maior número se sintomas de má digestão, cefaleia, sonolência diurna e insônia.

Abstract Objective To verify the quality of sleep, chronotype, and health characteristics associated with the sleep quality of students. Methods Descriptive, observational, and cross-sectional study with 204 undergraduate nursing students (age group 18-29 years, 91.6% female). A questionnaire was used for sociodemographic and health characterization. The Pittsburgh Sleep Quality Index Questionnaire and the Morningness-Eveningness Questionnaire were applied to verify the sleep quality and identify the chronotype, respectively. The association between health variables and sleep quality was analyzed. Results The majority of students was identified with preference for the indifferent chronotype (56.37%) and poor sleep quality (84.31%). There was an association between being a student and working, with symptoms of poor digestion, headache, daytime sleepiness and insomnia. Conclusion Nursing students have poor sleep quality and preference for the indifferent chronotype. Those who accumulate the study/work functions, present more symptoms of poor digestion, headache, daytime sleepiness and insomnia.