The effects of winter on ones mood

with distance from the equator a number of affected persons is bigger. There is known also that women, children and adolescents are more vulnerable and susceptible to this season-related mood disorder, which is widely known in medical literature as Seasonal Affective Disorder (SAD). This is a syndrome characterized by depressions that recur annually at the same time each year, usually during the winter months (MESH, 2005). In 1984 Rosenthal et al. described the major manifestations of seasonal affective disorder and last years it has got increasing attention of the researchers. But even after two decades of intensive studies the pathophysiology of SAD is still unclear. There were proposed several hypothesis of SAD pathogenesis. Thus in the late 1980s there was introduced phase-shift hypothesis which sees SAD as a result of a phase delay of the endogenous circadian oscillator relative to the sleep-wake cycle (Lewy et al., 1989). The series of neurophysiological researches focused on the role of metabolism of neurotransmitters and activity of some hormones (e.g. melatonin) in the development of seasonal affective disorder. For example Levitan et al., (1998), Schwartz et al. (1997) consider that SAD is associated with alterations in brain serotonin (5-HT) receptor function. Macchi amp. Bruce (2004) stated that humans are not photoperiodic organisms but the occurrence of seasonal affective disorder and its successful treatment is related to the activity of pineal gland and melatonin secretion. Many authors (Jang et al., 1997. Madden et al., 1996) argued that seasonal changes in mood and behavior could have heritable component in its origin. Multiple evidences suggest a genetic link between SAD and eating disorders, which possibly involve a number of serotonin-related genes (Levitan et al., 2004. Sher, 2001. Sorbi et al., 1998).
Eagles (2004) writes about the possible role of seasonal affective disorder as evolutionary adaptation. He considers that winter depression can be seen to be adaptive mechanism. The submissive behavioral pattern of seasonal depression assures survival for the current moment. Eagles wrote, depression may constitute an adaptive means of inactivity (ibid, p. 768). She linked winter mood changes with the benefits for hybernation, pro-recreational timing and healthier pregnancies. By her opinion SAD is even helpful for promoting nuclear family stability. She sees the origin of the problem of SAD in the nature of industrialized society where intensive work activity is required for all seasons and which accept evolutionary adaptive winter depression as a disorder.
There are widely used the various questionnaires for detecting seasonal mood changes. These instruments are often based on self-reporting of major depression signs. Seasonal Pattern Assessment Questionnaire, one of the oldest instruments for SAD screening, provide the possibility for diagnosis of SAD. Seasonal affect disorder could be defined if seasonality score on SPAQ is more than or equal to 11 points. Consequently, sub-syndromal SAD could be defined if seasonality score on SPAQ is 9 or 10 points (Eagles, 2004).
But without appropriate statistical tools there is impossible to give any evidence of the significance of research findings. Correlation analysis is used for describing the degree to which variable is associated with another one. The strength and direction of such association is showed by the correlation coefficient (see