Morningness-eveningness preference and mood in Japanese junior high school students.

The relationship between morningness-eveningness (M-E) preference and mood in Japanese students aged 12-15 years (690 boys and 649 girls) was investigated. No significant difference in M-E preference was seen between genders. Girls became gloomy more frequently than boys, whereby the girls who experienced melancholy more frequently tended to prefer evening. The correlation between mood and M-E preference, which was demonstrated only by girls, might be linked to a rapid shift to evening preference by girls in the past couple of years.