Mobile phones are commonly used by adolescents. The aim of this study was to clarify associations between duration of mobile phone use and psychological mood in high school students.

This cross-sectional study included 2,785 high school students in Niigata, Japan. A self-administered questionnaire was used to elicit information on sex, school year, hours of mobile phone use, psychological mood status, and possible confounders. Psychological mood outcomes were evaluated with the Mood Inventory, developed and validated in 1994, which includes five subcomponents with total scores ranging from 8 to 32 (higher score indicates stronger feeling): “Tension and excitement,” “Refreshing mood,” “Fatigue,” “Depressed mood,” and “Anxious mood.” Analysis of covariance with Bonferroni’s multiple comparison was used to compare mean values among quartiles of hours of mobile phone use.

Among the respondents, mean mobile phone use per week was 24 (median 18) h. Long-duration mobile phone use was associated with female students, no participation in sports club activities, early mobile phone use, and fewer hours spent sleeping (all P < 0.001). Overall associations between hours of mobile phone use and total scores were significant for “Depressed mood” (P for trend = 0.005), “Tension and excitement” (P for trend <0.001), and “Fatigue” (P for trend < 0.001). Total scores for “Depressed mood,” “Tension and excitement,” and “Fatigue” of the fourth quartile (≥33 h/week) of mobile phone use were significantly higher than for other quartiles (all P < 0.05).

Increased duration of mobile phone use is associated with unfavorable psychological mood, in particular, a depressed mood. Decreasing mobile phone use may help maintain appropriate mental health in very long-duration users.