Косова, А. Л. Chronotype, sleep length, and school achievement of 11- to 23-year-old students in northern European Russia / Borisenkov M. F., Perminova E. V., Kosova A. L. // Chronobiol. Int. - 2010. - Vol. 27. - P. 1259-1270.

1260 M. F. Borisenkov et al. chronotype of teenagers in the no rth ern latitudes. (Author correspondence: borisenkov@physiol.komisc.ru) Keywords Chronotype; Circadian rhythm; College students; N o rthern latitudes; School achievements; School children; Sleep length INTRODUCTION People differ in their optimal sleep length and time-of-day when they prefer to sleep (chronotype). The human chronotype is determined by the circadian system and represents the relationship between the phase of one’s endogenous rhythm and external synchronizers (Duguay & Cermakian, 2009; Roenneberg et al., 2003). Currently, the Horne- Ostberg questionnaire (MEQ) is widely used for estimating chronotype (Horne & Ostberg, 1976). The MEQ questionnaire detects early (“lark”), intermediate, and late (“owl”) types, giving a qualitative estimation of chronotype. This qualitative estimation of chronotype would be sufficient if defined only by genetic factors. However, it is known that apart from genetic factors (Hur, 2007; Jones et al., 1999), chronotype depends on a number of attributes, such as age, sex (Carskadon et al., 1993; Frey et al., 2009; Roenneberg et al., 2004; Tonetti et al., 2008), cultural traditions (Caci et al., 2005), and ecological factors (Roenneberg & Merrow, 2007). The recently developed Munich chronotype questionnaire (MCTQ) allows not only quantitative estimation of chronotype but also estimation of the influence of several external factors (Roenneberg et al., 2003). Recently, there has been a discussion about the possible effects of inadequate sleep (Ayas et al., 2003; McElroy et al., 2006) and the desyn­ chronization of the circadian system (Haus & Smolensky, 2006; Kantermann & Roenneberg, 2009; Stevens, 2005) on the development of chronic diseases, especially cancer. It is known that the risk of some chronic diseases is increased among inhabitants of northern latitudes (Anisimov et al., 2002; Tanuseputro et al., 2003). There is a 1.5-fold higher incidence of sleeplessness among adult inhabitants of the arctic zone than temperate areas (Nilssen et al., 1997; Ohayon & Partinen, 2002; Pallesen et al., 2001). In the arctic zone, sleep disturbances, e.g., difficulty initiating and maintaining sleep, early morning awakening, and nonrestorative sleep, are more often observed in the winter (Husby & Lingjaerde, 1990; Pallesen et al., 2001) and summer (Ohayon & Partinen, 2002) in the absence of the diurnal light-dark rhythm. The influence of climatic and latitudinal factors on human chronotype has been studied in countries located in low and southern latitudes. There is a prevalence of morning- oriented persons in the temperate climatic zone (Randier, 2008b; Smith, et al., 2002) and in the tropics (Randier, 2008b), whereas late-type teen­ agers are prevalent in the subtropics (Randier, 2008b). The influence of n i Q H T « L I N K 4 > 1 r u r i i t i - Г і в г - а г і а С я в і г :