SAN FRANCISCO (KRON) -- Spending more time on screens increases the likelihood that 9-year-olds and 10-year-olds will develop symptoms of mental illness, including anxiety and depression disorders, a new study by the University of California San Francisco found. The long-term study followed a diverse group of kids from around the country for two years. More screen time was associated with severe symptoms of depression, anxiety, inattention, and aggression, according to the study published Monday in BMC Public Health. “Screen use may replace time spent engaging in physical activity, sleep, socializing in-person and other behaviors that reduce depression and anxiety,” said the lead author Jason Nagata, associate professor at UCSF Benioff Children’s Hospital’s Division of Adolescent and Young Adult Medicine.  More than 9,500 children participated in the study. The study concluded, "Video chat, texting, videos, and video games were the screen types with the greatest associations with depressive symptoms. Future research should examine potential mechanisms linking screen use with child behavior problems." Fleet Week air show set to soar this week Adolescents' screen use has surged in recent years. The average time spent each day on screens for non-educational reasons is 5.5 hours for tweens, and 8.5 hours for teens, researchers said. The study states, "the COVID-19 pandemic led to worse mental health among adolescents, with 42% of high school students reporting persistent feelings of sadness or hopelessness, a 50% increase from 2011. Despite the increasing prevalence and burden of mental health problems in adolescents, these factors are complex, intertwined, and poorly understood." Parents can prevent negative effects of excessive screen time by setting rules. "The American Academy of Pediatrics recommends developing a Family Media Use Plan that considers the unique needs of each child," Nagata said.