A new study based on data from nearly 1,000 young people, ages 9-13, suggests how the amount of time spent on screens each day—TVs, computers, mobile phones, videogames—impacts depression risk at age 13. More specifically, the study relates screen use to sleep patterns and the structure of the brain’s white matter.

Recently, investigators led by BBRF Scientific Council member and 2008 Distinguished Investigator J. John Mann, M.D., having analyzed 4 years of data from a large study of U.S. youths ages 10-14, concluded that addictive use of phones, social media, and video games is commonplace, and is associated with 2 to 3 times higher rates of suicidal ideation and behaviors by age 14, as well as other mental health problems.

That study found that steadily increasing and addictive use of screen-based devices—but not “total screen time” per se—was associated with suicide-related and mental health outcomes. It did not mean to suggest, however, that total time spent on screens by young people is not an important factor in mental health. Long periods on the phone or other screen activities are well understood to crowd out sleep, exercise, and face-to-face contact in many users—none of which are healthy.

2021 BBRF Young Investigator João Paulo Lima Santos, M.D., of the University of Pittsburgh, devoted his grant to research that culminated in the new paper, which appears in the journal JAMA Pediatrics. He and colleagues wanted to know whether more screen time could impact sleep duration, and perhaps as a result of that, structural connectivity in the young, developing brain. One way of studying structural connectivity is via the brain’s white matter, which largely consists of axons and dendrites that link the human brain’s estimated 85 billion neurons. These connective “tracts” are called white matter because of their physical appearance: axons and dendrites are coated with a fatty insulation called myelin, which in microscopes appears off-white in color. Other members of the team included Amelia Versace, M.D., a 2009 BBRF Young Investigator, and Cecile D. Ladouceur, Ph.D., a 2006 BBRF Young Investigator, both also at the University of Pittsburgh.

“Time spent on screens is not necessarily harmful,” the team notes in its paper, pointing out that some studies of the question have found a weak or no relation between screen time and youth mental health. Some of these studies have, however, suggested a possible relation between use of screen-based devices and depression, “particularly during windows of developmental sensitivity such as early adolescence.”

The new study is predicated on the idea that such a possibility must be explored in greater detail. Sleep is critical for healthy neurodevelopment, “influencing the maturation of brain regions implicated in emotional regulation,” they note, “with noteworthy associations in early adolescence involving sleep duration and the brain’s gray and white matter.” Insufficient sleep and poor sleep quality are already known to raise the risk of depression in adolescents. How screen time might affect sleep and thus, indirectly, the question of depression risk is at the heart of the new study.

Like Dr. Mann’s team, the study led by Dr. Lima Santos made use of the remarkable dataset of the NIH’s Adolescent Brain Cognitive Development Study (ABCD), which recruited over 11,000 young people ages 9-11 at 21 U.S. sites and is following them through adolescence. The ABCD data is wide-ranging, and includes blood samples drawn periodically, as well as brain scans and various exams and questionnaires about mental health, completed both by young people and their parents/caretakers. The data analyzed in the current study was based on a subsample of 976 young people in the ABCD dataset, measured at two points: at the time of recruitment to the study (in this sample, average age between 9 and 10, i.e., “late childhood”); and at age 13 (“early adolescence”). About 47% were female; about two-thirds came from households with income $75,000 or greater; 63% were White, 18% Hispanic, and 5.5% Black.

Self-reported screen time at both time points was collected using a questionnaire that broke down activity into categories: watching TV and videos (“passive entertainment”); playing videogames (“active entertainment”); and texting, using social media, videochatting (“communication”). Sleep times were assessed via self-report questionnaire as well, and only at the later time point (age 13). Depressive symptoms were gauged via the well-validated Child Behavioral Checklist at both time points.

Studying white matter structure was a key part of the study. Early in life and through adolescence, white matter undergoes critical changes, including myelination and reorganization of axons and dendrites. External factors including physical injury can alter the process, as can inadequate or irregular sleep. To study white matter, the team used an imaging technology that enabled them to parse specific components affected by sleep and perhaps screen time. Called NODDI (neurite orientation dispersion and density imaging), it has previously established that “short sleep” in early adolescence is associated with decreased “coherence” in white matter tracts implicated in emotional regulation. These include the cingulum bundle, forceps minor, and uncinate fasciculus. These were under scrutiny in the brain scans from the study’s sample of 976 young people at the two study time points (ages 9-10 and 13).

After analyzing the data, this is what the team found: first, and perhaps most important, more daily screen time in late childhood (e.g., ages 9-10) was associated with more depressive symptoms in early adolescence (e.g., age 13). The attention to white matter paid off: the team found that the screen time/depression relationship was related to short sleep and diminished coherence of a particular white matter tract type, cingulum bundles. By this, the investigators mean that short nightly sleep duration and a deterioration of white matter organization were factors that correlated with the specific relations observed (with more screen time at age 9 or 10, more depression symptoms at age 13). This is not to say screen use or sleep time caused the white matter deterioration; separate studies must be conducted to prove such a relationship. But the factors do co-occur, this research indicates.

Another finding: 1 hour of daily screen time was associated with shorter sleep; 2 hours with more depressive symptoms, and 3 hours with worse organization of the white matter cingulum bundles.

Regarding “shorter sleep,” the team proposed several factors that may lie behind this: blue light from screens may disrupt melatonin, circadian rhythms, and sleep timing. Also, evening screen use, especially if stimulating, can delay bedtime and displace sleep.

Active and passive entertainment were linked with short sleep and white matter deterioration, but screen time devoted to communication did not appear to impact sleep duration, the study indicated. The authors noted that “this suggests that the relationships involving social media in early adolescence may be more nuanced, and components beyond screen time (such as actual content) should be explored.” Still, screen time may be found to be more relevant in the years just ahead, the team said, given that there has been an increase in social media use among children aged 8-12 years.

What about parental efforts to restrict screen time? The researchers are skeptical, calling these “impractical, especially for adolescents who rely on screens for other activities such as homework.”

“Altogether, the findings show that screens pose potential risks, but engaging parents, educators, and adolescents is essential to develop balanced strategies” that can address screen use and sleep “based on individual needs,” the team said.

In the end, the team feels their findings on white matter are the most important in the study: white matter is a key factor, they stressed, in understanding how screen time interacts with sleep to impact depression risk by age 13. “These findings underscore the importance of fostering healthy screen time habits and prioritizing adequate sleep to support emotional and brain development” they said, stressing that sleep habits, in particular, are something that are eminently modifiable to promote mental and physical health, assuming parents and children are willing to work on them.