Seasonal Variation of Human Mood and Behavior

Seasonal variations of mood, behavior and physiology have been of increasing interest. At least two different seasonal rhythms seem to exist: Descriptions of Seasonal Affective Disorder (SAD) with increased weight, increased sleep and fatigue during winter have attracted attention in academic psychiatry and in the general public the last two decades. In addition to such a difference in mood, weight and sleep between summer and winter, many studies describe a spring and fall increase in frequency of suicides and of admissions to hospital for mood disorders. In searching for a possible etiology for these seasonal changes, the main focus has been on variations in length of day. The objective of this thesis was to study the existence and pattern of seasonal variation in some forms of behavior and of psychiatric illness among children and adults in Norway. Possible statistical connections between seasonal variations of behavior and changes in length of day and the influences of latitude, sex and age were also studied. The monthly numbers of incidents in different groups were studied: All suicides in Norway 1969-96 (N=14.503), admissions to hospital for depression and mania in some hospitals 1992-96 (N=4.341), all violent episodes recorded by the police in Norway 1991-97 (N=82.537), all patient-staff incidents in a psychiatric department 1990-97 (N=502), all telephone calls to the Red Cross help-line for children and adolescents in Norway 1996-98 (N=691.787calls, 220.602 conversations) and in Trondheim, Norway 1991-97 (N=80.983 calls, 22.698 conversations) were included in the thesis. The monthly frequencies of these incidents were compared to an expected equal daily frequency of incidents through the year. Changes with increasing age and increasing latitude were examined. Correlations between the monthly frequencies of incidents and the length of day, with maximum impact at midsummer, and correlations between the monthly frequencies of incidents and the speed of change in length of day, with maximum impact at the equinoxes, were also studied. In this thesis, an increased activity in April-June and in October-November is described for all the groups that were studied. In summer and winter there is less activity than in the rest of the year. Among children calling the help-line, a steady diminishing seasonal variation in number of calls with increasing age from 7 to 17 years of age and an increasing seasonal variation in number of calls with increasing latitude were found. Also the seasonal variation of violence increases with increasing latitude in Norway. Among men there is a correlation between the monthly number of suicides and the monthly number of admissions for mania and a correlation between the monthly number of suicides and the monthly number of admissions for depression. Among women there is a diminishing seasonal variation of admissions for depressions with increasing age. The monthly frequency of violence in Norway and the monthly frequency of calls to the Red Cross help-Line for children and adolescents correlated with a delay of 1-2 months with the monthly change in length of day with maximum impact at the equinoxes. The results in the thesis correspond with earlier studies describing an increase in the frequency of suicides and an increase in admissions for depressions in spring and fall. A corresponding rhythm for other forms of human behavior is described in the present thesis, indicating that the seasonal rhythm of psychiatric illness reflects a seasonal rhythm of behavior in greater parts of the population. The seasonal variation in behavior seems to increase with increasing latitude, to be more dramatic in the northern than in the southern parts of Norway. In this thesis results supporting a hypothesis of human behavior being influenced by changes in length of day are given. Changes in length of day may induce changes in sleep and other disturbances in the daily rhythm that could change mood and other emotional qualities in vulnerable individuals. The demands on our capability to adapt to changes in length of day are largest at the equinoxes