Impact of perinatal photoperiod on the chronotype of 11- to 18-year-olds in northern European Russia.

The study investigates the effect of the month of birth and ambient light conditions at birth on sleep length and chronotype among residents of high latitudes. The authors surveyed 1172 persons (609 girls, 563 boys) age 11 to 18 yrs living in five villages and four towns located between 59.5°N and 67.6°N latitude. Survey participation was voluntary and anonymous. Sleep length and chronotype were assessed using the Munich chronotype questionnaire (MCTQ). The study showed the sleep length and chronotype of the children and adolescents depended on sex, age, type of settlement (town/village), and latitude of residence. Latitude exerted a stronger impact on sleep length and chronotype of children and adolescents living in villages than on those of their urban counterparts. Month of birth had no effect on sleep length and chronotype. There was a significant effect of the time of sunrise, sunset, and day length at birth on the chronotype of children and adolescents. A later chronotype was observed in the sample of young persons living above the Arctic Circle who were born during the polar day and polar night.