High Serum Cortisol Levels as a Potential Indicator for Changes in Well-Regulated Daily Life among Junior High School...

Problematic smartphone use among adolescents has become a social concern and is associated with poor sleep quality. The relationship between life habits, such as smartphone use and sleep duration, and levels of immunological and neuroendocrine biomarkers, including the stress hormone cortisol, in adolescents seems to be important to objectively comprehend their health and well-being in school life. However, such a relationship has not been well documented. We therefore studied rural junior high school students in Japan to elucidate the relationship between serum cortisol (SC) levels and their life habits. A total of 155 students in the seventh grade in 2016 were recruited as subjects. Of them, 140 students with eligible responses and blood samples (12-13 years; 80 boys, 60 girls) were finally included in the study (response rate 90.3%). A questionnaire survey concerning wake-up time, sleep duration, and the length of time using a smartphone per day was conducted. Blood samples were collected from peripheral veins of participants under fasting conditions between 8:30 and 11:00 a.m. The Spearman rank correlation coefficients were as follows: between SC and wake-up time, 0.199 (p = 0.018); between SC and sleep duration, 0.185 (p = 0.029); and between SC and time spent on smartphones, 0.172 (p = 0.042). The multiple regression analysis showed that high SC levels were significantly associated with late wake-up time and with short sleep duration. We therefore propose that measuring SC levels is useful for early detection of the change in the well-regulated daily life among junior high school students.