Chronotype, sleep length, and school achievement of 11- to 23-year-old students in northern European Russia.

Residing at northern latitudes for long periods of time is associated with sleep disturbances and internal desynchronization, which are considered to be causes of chronic diseases in old age. In children and teenagers, they result in a poor school achievement, psychological problems, and increase in consumption of stimulants. In this paper, we analyze the relationship between both chronotype and sleep length and the variables of age, sex, place of residence, type of settlement (village/city), latitude and longitude of residence, and school achievement of young inhabitants of northern European Russia. We surveyed 1101 children and teenagers between 11 to 23 yrs of age living in four settlements located between 59 degrees and 67 degrees North latitude and 33 degrees and 60 degrees East longitude. The Munich chronotype questionnaire (MCTQ) was used in the study, and all participants were also required to answer a question about their school achievements. An analysis of covariance (ANCOVA) was used to assess the influence of the analyzed factors on sleep length and chronotype. Self-reported sleep length of teenagers depended moderately on age, whereas the place of residence, latitude, and type of settlement only had a weak effect. Chronotype strongly depended on place of residence and longitude; it moderately depended on latitude and age; and it weakly depended on sex and type of settlement. The sleep length of village teenagers was 46 min longer than that of urban teenagers. The authors found a 1 h and 18 min phase delay of the sleep-wake rhythm (as a marker of chronotype) in teenagers moving in the East-West direction and a 16-min delay moving in the South-North direction within one time zone. There was a weak, but significant, positive correlation between chronotype and time of sunrise. There was about a 2-fold stronger influence of chronotype than sleep length on achievement of school children and college students. We conclude that socioeconomic factors exert a significant influence on sleep length and that climatic conditions exert a significant influence on the chronotype of teenagers in the northern latitudes.