Hyperthymic Temperament and Sunshine: A Study of 3 Regions in Japan Kentaro Kohno a, Hajime Baba b,c, Takeshi Inoue d Yukiei Nakai d, Atsuhito Toyomaki d, Toshihito Suzuki b,c Koji Hatano a,e, Heii Arai b,c, Takeshi Terao a 2014May9-12 IRPB in Athens, Greece a Department of Neuropsychiatry, Oita University Faculty of Medicine b Department of Psychiatry, Juntendo University School of Medicine c Department of Psychiatry, Juntendo Koshigaya Hospital d Department of Psychiatry, Hokkaido University Graduate School of Medicine e Department of Psychiatry, Eto Hospital

Introduction In a previous study examining the association of hyperthymic temperament and daily light exposure (illuminance), we compared hyperthymic scores of the Temperament Evaluation of Memphis, Pisa, Paris and San Diego-auto questionnaire version (TEMPS-A) acquired from residents in Sapporo and Oita in Japan, which are located at 43˚ and 33˚ of latitude. However, the comparison of two regions may not be sufficient to clarify the association between hyperthymic temperament and illuminance because other factors that are specific to each region than illuminance may be associated with hyperthymic temperament. In order to avoid such possibility, it is reasonable to investigate a dose-response relationship among 3 regions. In the present study, another region of Koshigaya, which is located at 36˚, was added to Sapporo and Oita. The association between hyperthymic scores and sunshine was investigated among these 3 regions.

Method Subjects 125 medical students and staff from Juntendo Koshigaya Hospital in Koshigaya participated newly to the present study. Their data were combined with the previous data (Kohno et al., 2012) of 94 medical students and staff from Hokkaido University in Sapporo, and 95 medical students and staff from Oita University in Oita. In total, the data of 314 subjects was collected with a mean age of 31.5 ± 8.4 (SD). There were 175 males and 139 females. All subjects were screened for present and past psychiatric disorder and none suffered from psychiatric disorders. Written informed consent was obtained from all the subjects and the study was approved by all three of the relevant university ethical committees. Temperament assessment The subjects completed the Japanese standardized version of the Temperament Evaluation of Memphis, Pisa, Paris and San Diego-auto questionnaire version (TEMPS-A), which is a 110-item true false questionnaire measuring the temperament dimensions: depressive, cyclothymic, hyperthymic, irritable and anxious (Matsumoto et al., 2005).

Illuminance As a parameter of illuminance among Sapporo, Koshigaya, and Oita, the mean yearly total sunshine of the past 20 years ( ) was used. Statistical analyses First, age and sunshine were compared between Sapporo, Koshigaya and Oita by analysis of variance (ANOVA). Post-hoc analysis was performed by Fisher’s PLSD. Gender ratio was compared among 3 cities by χ 2 test. Secondly, Pearson's correlation coefficient was used to test correlations of 5 temperament scores, age, gender, and sunshine. Finally, multiple regression analysis was used to identify factors associated with hyperthymic temperament scores of TEMPS-A. Furthermore, multicollinearity was investigated.

Table 1: Subject demographics and the mean yearly total sunshine for 20 years (1993 to 2012) in Sapporo, Koshigaya and Oita VariablesSapporoKoshigayaOitaF or χ2 value Post-hoc comparison c N Age (mean±SD) 29.4± ± ± a ***Sapporo<Koshigay a*** Sapporo>Oita* Koshigaya>Oita*** gender (M/F)66/2842/8367/ b *** latitude43°36°33° Sunshine (h, mean±SD) ± ± ± a ***Sapporo<Koshigay a*** Sapporo<Oita*** Koshigaya<Oita*** Results a ANOVA, b χ 2 test, c Fisher’s protected least significant difference test *: p<0.05, **: p<0.01, ***: p<0.001 The subjects of Koshigaya were significantly older than those of Sapporo while those of Sapporo were significantly older than Oita. Gender ratio was significantly different among 3 regions. Sapporo had significantly less sunshine than Koshigaya by 178 hours per year while Koshigaya had significantly less sunshine than Oita by 140 hours per year.

Table 2: Correlations of 5 temperaments, age, gender, and sunshine AgeGenderDepCycHypIrrAnxSunshine Age ** * Gender * Dep *** ***0.57***0.13* Cyc ***0.62***0.57***0.13* Hyp *** * Irr ***0.05 Anx sunshine1.00 Dep: depressive temperament, Cyc: cyclothymic temperament, Hyp: hyperthymic temperament, Irr: irritable temperament, Anx: anxious temperament, gender: female=1, male=2, sunshine: Sapporo= h, Koshigaya= h, Oita= h. *p<0.05, **p<0.01, *** p< Depressive, cyclothymic and hyperthymic temperament scores were significantly and positively associated with sunshine.

Table 3: Multiple regression analysis of hyperthymic temperament. Betap Dep Cyc Irr0.31< Anx Age Gender Sunshine R 2 (adjusted R 2 )0.19 (0.17)< Dep: depressive temperament, Cyc: Cyclothymic temperament, Irr: irritable temperament, Anx: anxious temperament, gender: female=1, male=2, sunshine: Sapporo= h, Koshigaya= h, Oita= h Hyperthymic temperament scores were significantly and positively associated with cyclothymic and irritable temperament scores and sunshine, and significantly and negatively associated with depressive and anxious temperament scores independently. Multicollinearlity was denied in this multiple regression analysis.

Discussion and Conclusion The main findings of the present study are that by multiple regression analyses sunshine predicted significant variance of hyperthymic temperament scores in a dose-dependent manner without multicollinearity. Therefore, it is strongly suggested that higher illuminance may maintain hyperthymic temperament via light effects. In considering these findings, it is important to note that temperature decreases as sunshine decreases amongst these 3 regions. Therefore, it cannot be completely denied that higher temperature itself may maintain hyperthymic temperament. Unfortunately, we could not examine this possibility with the present data due to the effect of multicollinearity when both sunshine and temperature were put in the multiple regression analysis together. It is the limitation of the present study. In conclusion, the present findings suggest that higher illuminance may maintain hyperthymic temperament via light effects.