Does temperature or sunshine mediate the effect of latitude on affective temperaments? A study of 5 regions in Japan.

BACKGROUND Previously, we compared the hyperthymic scores of residents in Sapporo, Koshigaya, and Oita (which are located at latitudes of 43°N, 36°N, and 33°N in Japan, respectively) using the Temperament Evaluation of Memphis, Pisa, Paris and San Diego-auto questionnaire version (TEMPS-A). We found that residents who lived at lower latitudes had higher hyperthymic temperament scores; however, the mechanism of the effect of latitude on hyperthymic temperament remained unclear. The current study examined the mediators of the latitude effect in additional regions with different annual temperatures and amounts of ambient sunshine. METHODS The Japanese archipelago stretches over 4000 km from north to south and has four large islands: Hokkaido, Honshu, Shikoku, and Kyushu. In addition to the TEMPS-A previously reported data collected at Sapporo (latitude 43°N), Koshigaya (36°N), and Oita (33°N), we collected the TEMPS-A data of 189 and 106 residents from Takaoka (36°N) and Obihiro (42°N), respectively. Taken together, these five regions have different patterns (i.e., highs and lows) of annual ambient total sunshine (hours) and mean temperature (°C). The effect of latitude, sunshine, and temperature on affective temperaments was analyzed for five Japanese regions. RESULTS Multiple regression analyses revealed that latitude predicted significant variance in hyperthymic temperament. Ambient temperature, but not sunshine, significantly affected hyperthymic temperament. LIMITATIONS The light exposure that residents actually received was not measured. The number of regions studied was limited. The findings might not generalize to residents across Japan or other countries. CONCLUSIONS The present findings suggest that latitude affects hyperthymic temperament, and ambient temperature might mediate this effect.