Abstract The popularization of the use of electronic has become a global trend, and children are exposed to devices at younger ages. A large proportion of children and adolescents spend on screen time more than 2 h which is recommended in most guidelines. The paper reviews possible effects of screen time on physical and mental health, as well as mental disorders in children and adolescents. It is found that excessive screen time showed negative impacts on mental health, including depression, anxiety, mood disorder, social adaptational problems, behavioral disorders, self injurious behaviors, and health risk behaviors. Much attention has been paid on the association between excessive screen time and mental health of children and adolescents, while possible mechanisms and influencing factors are lacking. Effective intervention studies are needed to provide a basis for child and adolescent health promotion.

【Objective】 To explore the status quo and influencing factors of knowledge, attitude and practice of voluntary blood donation among undergraduates in Beijing. 【Methods】 A questionnaire was designed on the basis of literature, using the method of convenience sampling to survey the undergraduates from 39 universities in Beijing. The t-test, analysis of variance and χ² test were used to compare the differences in knowledge, attitude and practice of voluntary blood donation among different groups, and logistic regression model was performed to analyze the influencing factors. 【Results】 A total of 1 075 valid questionnaires were collected from undergraduates of 39 universities in Beijing. The results showed that the proportion of the participants who had good knowledge about voluntary blood donation was 69.21% (744/1 075). No statistically significant difference was noticed on the scores of voluntary blood donation knowledge between males and females (P>0.05). The scores of voluntary blood donation knowledge of medical students were higher than those of other subjects (P<0.05). The scores of voluntary blood donation knowledge of juniors and above were higher than those of lower grades (P<0.05). The rate of undergraduates participating voluntary blood donation in Beijing was 30.98% (333/1 075). A total of 67.26% (723/1 075) of students had donation intention, 9.49% (102/1 075) didn’t and 23.25% (250/1 075) were not sure. No statistically significant differences in blood donation intention were observed among undergraduates by genders and grades (P>0.05). The rate of medical students’ intention to donate blood was higher than that of other subjects (P<0.05). 【Conclusion】 The rate of voluntary blood donation among undergraduates in Beijing was above the middle level compared with other regions in China, but the practice of voluntary blood donation is far away from the intention. Therefore, it’s necessary to improve the level of knowledge, attitude and practice of undergraduates, especially non-medical college students, so as to improve the rate of voluntary blood donation among the undergraduates in Beijing.