Using data from the Centers for Medicare and Medicaid Services (CMS) and the United States (US) Census Bureau, Matthews and colleagues [1] estimated a 178% increase from 2014 to 2060 for the number of Americans projected to have ADRD. This reflects a growth in both aging and minority populations and assumes trends in 2014 will remain constant [1]. Matthews and colleagues [1] suggest that since their estimates are based solely upon unchangeable risk factors for ADRD, other modifiable factors such as educational attainment which tend to have protective effects against dementias may result in an overestimate for future decades. We will argue that not only is the Matthews and colleagues [1] projection not an overestimate, but it is a significant underestimate based upon additional data showing several critical differences between populations aged $\ge$65 in 2014 compared to 2060. These additional factors include a decline in intelligence [3], despite greater educational attainment [43], and an increase in screen time [44], due to greater access to mobile digital devices, both of which occurred post-1975. Converging research suggests that the negative effects of excessive screen time include impairments in learning, memory, attention, concentration, emotional regulation, and social functioning in young adults that are similar to symptoms of MCI observed in older adults and that typically precede the development of ADRD. MCI is a diagnostic category thought to be a transitional stage from normal to pathological aging, and is characterized by the following minimal impairments to instrumental activities of daily living in the absence of dementia: complaint or history of cognitive decline/impairment, objective evidence of impairment in attention, memory, language, visuospatial skills or executive function, and impairments in normal functional activities [45].

ADRDs are progressive brain disorders characterized by gradual and increasing impairments in attention, concentration, and orientation, short-term and long-term memory, activities of daily living, and reasoning and decision making abilities [22, 46]. At the end stages of ADRD, individuals are usually non-verbal, non-ambulatory and unresponsive to their surroundings [46]. The progression from early to end stages of ADRD also include profound changes in personality, mood and social interactions, including anterograde amnesia (i.e., inability to acquire new memories), retrograde amnesia (i.e., trouble recalling past memories), and even psychiatric symptoms such as delusions and hallucinations [46, 47]. Those with ADRD also show poorer social functioning and self-care routines, score higher on tests of anxiety, and have greater sleep disturbances [48, 49].

Studies show that regional and global cerebral atrophy rates are well correlated with progressive cognitive-behavioural declines characteristic of Alzheimer’s disease (AD) [50, 51, 52, 53, 54, 55]. Progressive cerebral atrophy is associated with the stages of AD [52, 54]. Pre-symptomatic and mildly affected individuals show significant volume loss in the hippocampus and posterior cingulate and neocortical temporoparietal cortices; in contrast, moderately and severely symptomatic individuals show more widespread cerebral atrophy, particularly in the inferolateral areas and frontal lobes with some sparing of the primary motor and sensory areas and cerebellum [52, 54]. Volumetric changes in the hippocampus, entorhinal cortex, whole brain, and ventricles predicted conversions from preclinical (i.e., no symptoms) to clinical stages of MCI or AD and from MCI to AD and were more reliable predictors than standard psychometric measures [53]. For individuals over age 60, gray matter volume decreases of approximately 2% per year are seen in patients with AD compared to controls [50] and significant losses in white matter essential for communication between brain regions [30, 34, 35, 51, 56]. Reduced cortical thickness in the posterior cingulate gyrus is characteristic of AD in both typical and atypical clinical presentations [57]. These findings demonstrate that cerebral volume is a robust indicator of MCI and ADRD in middle to late adulthood. Factors that may increase cerebral volume loss in early adulthood, or even prevent cerebral volume growth in childhood and adolescence, may greatly accelerate the cognitive-behavioural signs of neurodegeneration in middle adulthood and significantly increase the rates of MCI and ADRD. We will argue that excessive screen time in childhood, adolescence, and early adulthood impairs brain development leading to reduced overall CBBR before middle adulthood increasing the risk of neurodegeneration potentially 10 to 20 years earlier than expected.

The Flynn effect refers to the increasing performance over time on intelligence tests across the population throughout the 20th century [3, 58, 59, 60, 61]. Studies show increases of approximately 2.50 to 3.00 IQ points per decade with proposed explanations focusing on biological factors (e.g., nutrition, pathogen stress, fertility) and environmental factors (e.g., education, family size, technology, test-taking behaviour) and the interactions between them, referred to as ‘social multipliers’ (i.e., any environmental factor that confers an advantage improving test performance) [62]. Analyses show substantial gains in fluid IQ (i.e., reasoning-based performance) that are greater than gains for crystallized IQ (i.e., knowledge-based performance), greater gains for adults than children, and positive correlations with economic gains (i.e., GPD growth) [62]. Results also show a deceleration or reversal of gains in recent decades [62].

The reversal of this trend in IQ gains, referred to as the negative Flynn effect, has been documented in several countries in post-1975 birth cohorts [2, 3, 58, 62]. The main contributors to the Flynn effect are thought to be environmental and generate within-family variation based upon exposure differences (e.g., age at exposure, exposure duration), although the specific mechanisms underlying these environmental effects are unclear [3]. The negative Flynn effect may reflect a ceiling effect for environmental advantages (e.g., saturation or diminishing returns) or increases in social multipliers detrimental to IQ (e.g., dysgenic fertility, immigration, declining educational standards) [3, 62]. Although exposure to technology is postulated to positively affect IQ by providing greater visual stimulation, evidence does not support a link between increased fluid IQ and frequency of visual media exposure [62]. In fact, evidence is emerging that excessive screen time may be a significant negative social multiplier contributing to the deceleration and decline of population IQ. The negative Flynn effect starting post-1975 is paralleled by a decline in vocabulary, documented from 1974 to 2016 for American adults; this is despite an increase in educational attainment (e.g., 11.83 to 13.68 years of school completed), which is generally correlated with verbal intelligence [43]. During this same time period, there has been a significant decrease in reading print (e.g., books, magazines, newspapers) and a critical increase in digital screen exposure (e.g., television, computers, tablets, smartphones) [44]. In a study examining reading comprehension, it was found that students who read from print scored significantly higher on reading comprehension tests than those who read the text digitally [8]. Several explanations were proposed: (i) navigation via scrolling on screens is known to negatively interfere with mental representations of text, (ii) multitasking on a computer (e.g., switching screens to read or answer questions) has hidden cognitive processing and memory costs (e.g., increasing challenges of dividing attentional resources), and (iii) metacognitive and self-regulation skills (i.e., ability to monitor and adapt one’s cognitive performance to a task) may have been engaged more with print media, traditionally used for effortful learning, compared to digital media, often used for quick and superficial information gathering [8]. Evidence suggests there are detrimental consequences of excessive screen time for attention, learning, memory, and language development [4]. Research shows that screen time is increasingly replacing time spent on academics for adolescent and young adult students [43, 44, 62] and constant use of digital devices is associated with worse reading comprehension, word reading and vocabulary [8], which may impact overall IQ levels.

The amount of screen time exposure during critical periods of brain development differs significantly for the Silent Generation (born 1925 to 1945), Baby Boomers (born 1946 to 1964), and Generation X (born 1965 to 1979) compared to Millennials (born 1980 to 1995) and Generation Z (born 1996 to 2012). Compared to previous generations, the average 17–19-year-old spends approximately 6 hours a day on mobile digital devices (MDD) (e.g., smartphones, tablets, and laptop computers) [44] whereas individuals born before 1965, the Silent Generation and Baby Boomers, at the same age spent zero hours on MDD. Generation Z is the first in history to never know a world without the Internet; Generation Z surpasses passes Millennials on social media use by almost 3 hours each day [63].

Adolescent screen time use has changed dramatically from 2.5 hours a day of TV viewing in 1970 to almost 8 hours a day of TV viewing, internet use, texting, and social media use in 2016 [44]. This represents at least a 3-fold increase in screen use for adolescents as these numbers were reported for leisure time and do not include screen use at work, school or studying [44]. Even the time spent viewing television may be fundamentally different across cohorts as Generation Z increasingly engages in multiscreen use [64, 65, 66, 67, 68] which is known to have negative effects on cognitive processing including attention, memory, learning, and comprehension [69, 70, 71, 72, 73]. Overall, Generation Z spends more time online and texting and less time with more traditional media such as magazines, books, and television than previous generations [44].

Excessive screen time affects brain structure and function, particularly during development, which greatly impacts attentional and inhibitory control, focused concentration, learning, memory, reasoning, and creativity [10, 74, 75, 76]. These basic capacities are essential for executive control in goal-directed and decision-making behaviours which underlie human intelligence and the essential “ability to adapt to uncertain, changing, and open-ended environments” [74] (pp. 1). If the neural circuits underlying these cognitive-behavioural abilities essential for general intelligence and lifetime adaptability are under- or abnormally-developed before adulthood, then it is likely that these changes will persist into early and middle adulthood and be more vulnerable to accelerated neurodegeneration in late adulthood. Brain development occurs in stages and is marked by periods of massive plasticity (i.e., major neuronal and synaptic rearrangement), particularly the perinatal and periadolescent transitions, the latter of which is characterized by significant gray matter reductions and white matter increases that correspond to cognitive-behavioural maturation [77, 78, 79]. Neuroimaging studies of connectivity in the brain suggest several dynamic brain networks governing executive functions, intelligence, and social-emotional behaviour emerge early in brain development, increase their functional interactions during adolescence, and variations in patterns of connectivity can predict healthy and pathological trajectories of development into adulthood [22, 80, 81, 82]. Changes in these cortical networks are thought to be influenced by early environmental experiences, including childhood abuse [83], urban upbringing [84], and screen time [33], and may have serious lifetime impacts on general cognitive ability, social-emotional behaviour, psychopathology, and substance use and abuse. Studies show that abnormal patterns of regional connectivity, specifically in frontal and parietal lobe connections, are also found in neurodegenerative conditions including ADRDs, particularly frontotemporal dementia and AD [22].

Preliminary data from The Adolescent Brain and Cognitive Development (ABCD) Study, a multi-site longitudinal neuroimaging study, shows the significant impact that screen time has on the relationship between cognitive-behavioural maturational markers and normal patterns of brain development in children and adolescents [33, 85]. The study identified several associations between screen time, brain structure (e.g., cortical thickness, gray matter volume, and sulcal depth), and cognition (e.g., fluid and crystallized intelligence) and mental health (e.g., internalizing and externalizing psychopathologies) [33]. First, results showed a robust association between screen time and changes in visual system structural patterns (i.e., reduced volume, thinner cortex, variations in sulcal depth), which may negatively affect the functioning of other cortical networks, such as cognitive control regions, that interact with sensorimotor areas [33]. Second, results showed a strong association between screen time, externalizing (but not internalizing) psychopathology, and changes in cortical and limbic structures (e.g., smaller orbitofrontal volume, thinner occipital and temporal cortices, thinner hippocampi) [33], which may help explain the concomitant rise in screen time and disorders of attention and hyperactivity (reviewed in [4]). Third, results showed a more complex pattern of association between screen time, particularly type (e.g., gaming versus social media), and brain structure changes and measures of fluid and crystallized intelligence. For fluid intelligence, gaming activity showed positive associations with prefrontal cortex thinning, whereas social media activity showed negative associations with hippocampal thickness and temporal lobe volume [33]. In contrast, for crystallized intelligence, screen time in general and social media activity showed strong negative associations with occipital and orbitofrontal volume [33]. In a study of young adults, it was demonstrated that excessive social media use is associated with gray matter volume reduction in the bilateral amygdala and right ventral striatum but not the prefrontal cortex [29], suggesting that excess behaviour arises from a developmental disruption of reward-learning [29].

Taken together, these results contribute to evidence from brain imaging and behaviour studies that support the dual system theory of excess problematic behavior [86] which proposes that the development of these abnormal behaviors arises from imbalances between the reward system (mesolimbic dopamine amygdalastriatal) which becomes hyperactive and the inhibition system (prefrontal regions) which becomes hypo-active [29]. Such imbalances have important implications for focusing attention, learning, memory, intelligence, social-emotional regulation, and behavioural addictions. Based on models of drug, alcohol, and gambling addictions, characteristic traits of internet addiction include fixation with playing online games, repeated failed attempts at cessation, increased negative affect, neglecting significant relationships or activities, and the development of tolerance and withdrawal symptoms [30, 35, 36]. Studies show internet addiction is associated with important changes in both gray and white matter in the developing brain, including volumetric loss and functional impairments related to behavioural abnormalities (e.g., impaired cognitive ability and control) [30, 34, 35, 36, 87]. For example, individuals with internet addiction showed abnormalities in cortical thickness in several areas involved in cognitive control including the frontal lobe, left lateral orbitofrontal cortex, insula cortex, lingual gyrus, right postcentral gyrus, entorhinal cortex, and inferior parietal cortex [35]. The frontal lobe performs executive functions, such as planning and organizing, and undergoes massive changes from puberty until mid-twenties [74]. The frontal lobe along with volume loss in the striatum, which includes the reward pathway and suppression of impulses, is seen to be affected by gray matter atrophy and white matter volumes; those with gaming addiction showed significant gray matter atrophy in the right orbitofrontal cortex, bilateral insula, and right supplementary motor area [34]. A functional magnetic resonance imaging study found that there is less efficient information processing and a reduced impulse inhibition in those with an internet addiction disorder, along with an increased sensitivity to rewards and an insensitivity to loss was exhibited [88, 89]. It was identified that those with an internet addiction disorder had abnormal spontaneous brain activity that correlated with poor task performance [35].

Thus, these studies suggest that early reductions in brain volume and functional capacity during brain development may increase the risk of MCI and ADRD which are characterized by significant white and gray matter loss and a deterioration in instrumental activities of daily living. This is consistent with the cognitive-behavioural-brain reserve (CBBR) hypothesis of dementia. Studies show that brain reserve is positively correlated with IQ, educational attainment, and engagement in cognitively stimulating occupational and leisurely activities, and negatively correlated with the transition from MCI to dementia [5, 90].

The term digital dementia was first coined by the neuroscientist Manfred Spitzer to refer to the literal ‘mind-deteriorating’ effects of digital technology; specifically, that excessive use of digital devices is associated with cognitive impairments characteristic of dementia, such as decreased attention and impaired memory, and these effects are being seen increasingly in younger adults not expected to be experiencing neurodegeneration characteristic of old age [91, 92, 93]. For example, Generation Z children began regularly watching television by 3 months of age [94] compared to 4 years of age for Generation X children [95]. Previous research indicates that earlier and longer exposures to screen time are associated with increased risk of psychiatric conditions (i.e., attentional problems and hyperactivity, anxiety, and depression) [19, 39], further suggesting that Generation Z children would be more likely to exhibit learning and memory impairments when compared to Generation X children.

Excessive screen time was found to be associated with problems in meeting developmental milestones for motor skills, spatio-temporal abilities, problem solving and language acquisition [7]. Content, pace, and degree of exposure were associated with dysfunction in attention, learning, and memory for both infants and children [6, 13]. For example, observational experiments in humans and animals determined that excessive sensory stimulation and exposure to fast-paced television during infancy and childhood resulted in cognitive and behavioural deficits [13]. Similarly, television programs which encourage active participation facilitated greater vocabulary acquisition when compared to passive programming [6]. A decline in performance on cognitive tasks was also observed in children who had over two hours of screen time per day and children exposed to seven or more hours of screen time per day revealed significantly reduced orbitofrontal thickness [32], a fundamental structure in the reward circuit pathway responsible for decision-making and addiction disorders in adolescence and adulthood [25, 31, 96].

The consequences of digital technology are associated with prolonged effects in adulthood. For example, post-secondary students scored significantly higher on midterms and exams in classrooms that prohibited the use of electronic devices in comparison to classrooms that did not prohibit the use of electronic devices [9]. In the general population, long-term effects of excessive screen time were associated with reductions in long-term memory and cognitive development [9]. In addition, many adults rely on technology and smartphones as opposed to cultivating self-imposed analytical thinking [76]. For instance, three studies examining smartphone use and cognition determined that individuals who thought more intuitively were more likely to rely on their smartphones for information when compared to individuals who thought more analytically [76]. Since search engines allow easy access of information, users are more prone to remember where to locate a fact instead of remembering the fact itself [10]. This can be seen when dealing with difficult questions: users tend to think more about searching for solutions online as they have a decreased recollection of the information and an enhanced recollection for where to access it [10].

Excessive screen time involving task switching between multiple screens also has harmful effects on memory, especially explicit memory which consists of episodic and semantic memory [97]. Episodic memory involves the recollection of autobiographical events from the past occurring in specific spatial and temporal contexts [98]. However, an overuse of digital recording of events (e.g., digital pictures, videos, etc.) may result in a loss of episodic memories as one begins to rely on external storage for memory rather than encoding it in the brain [97]. In a study evaluating the effects of using social media to record or share one’s experiences, it was found that participants who did not use social media consistently remembered their experiences more accurately than those who used social media [11]. These results suggest that using digital media may prevent people from remembering the very events they are attempting to preserve [11]. Semantic memory is described as the general knowledge and recall of factual information [98]. Information on the internet is often presented in hypertexts permitting users to scan information superficially which can lead to poor memory recollection [37]. Digital media adapts at a rapid pace, producing fundamental changes in written word or text (e.g., internet shorthand such as acronyms, keyboard symbols and abbreviations) [99]. Constant literary changes impede one’s ability to internalize the categorical rules of language like verb conjugation, spelling, and punctuation. Today, penmanship is dramatically diminished, which may drastically impact future generations more significantly because it serves as a tool for learning and consolidating memories [99].

In a study that evaluated the concept of digital dementia, the starting age and amount of mobile device use were potential factors leading to cognitive decline in males and females either under 20 years old or over 21 [75]. Excessive screen time is also associated with decreased attention and memory ability, alongside a greater amount of stress endured [75]. Generation Z may be a high-risk population for ADRD due to their heavy reliance on technology during critical periods of brain development and maturation. Many symptoms of excessive screen time parallel early cognitive decline as language and memory are severely impaired.

The rise of infant television viewing started in the late 1990s and has only become progressively more common [100]. The United States has seen a 10-fold rise in the incidence of attention-deficit disorder diagnoses in the past 20 years [100]. Television exposure early on is associated with attentional problems; in one study, 10% of children aged 1 to 3 developed attentional problems as early as the age of 7 [12]. Children viewed an average of 2.2 hours of television per day at age 1 and 3.6 hours per day at age 3. A one point standard deviation increase in the number of hours of television watched at age 1 is linked with a 28% rise in the likelihood of having attentional problems at age 7 [12].

Furthermore, increased multitasking on digital devices, particularly during study time, increases the risk of poor academic progress for adolescents and young adults [9, 14]. Interestingly, another study proposing a brain drain hypothesis for the effects of digital technology on cognition demonstrated that even when people are successful at maintaining sustained attention and avoid checking their phones, the mere presence of these devices still reduces available cognitive capacity [16]. The presence of a smartphone can adversely affect two measures of cognitive capacity, working memory capacity and functional fluid intelligence; both were negatively affected in those who had the highest rates of smartphone dependence [16].

Lastly, “digital natives”, such as Generation Z, are generations that grow up with internet technologies and drift towards a shallow information processing behavior distinguished by rapid attention shifting [37]. They also display higher incidence of internet-related addictive behaviors that reflect changed reward-processing and self-control mechanisms. Neuroimaging investigations have indicated associations between these internet-related cognitive effects and fundamental alterations in the brain [37]. A study that analyzed multitasking between different generations found that Millennials and Generation Z reported more multitasking than Generation X, who reported more multitasking than the Baby Boomers [14]. Generation Z differs significantly than Baby Boomers as they engage in heightened multitasking activities which are related to increased distractibility and poor executive control abilities [14]. Attention is necessary for all cognitive activities, and impairments in attention in adolescence and early adulthood that persist into middle and late adulthood may greatly reduce overall brain reserve leading to greater risk and early signs of MCI and ADRD [101, 102].

Generation Z individuals see their friends in person an hour less a day than Millennials did at similar ages [41]. On average, Generation Z adolescents in Grade 12 spend approximately 2 hours a day texting, 2 hours a day on the internet (including gaming) and 2 hours a day on social media for a total of 6 hours a day of screen time [44]. When the smartphones became more available around 2010, fewer adolescents reported that they were happy [20]. Adolescents who scored high on-screen use were significantly more likely to display poor emotion regulation, an inability to stay calm, irritability, uncooperative attitudes, lower productivity and curiosity, and damaged sociability [20]. Poor mental health is correlated with excessive screen time (any more than 2 hours per day), less sleep, or decreased in-person interactions [44]. Excessive screen use contributes to a sedentary lifestyle which is associated with reduced physical activity, lower vascular fitness, and an increased incidence of being overweight or obese [40]. In a 2007 survey it was found that 20.8% of 6 to 11-year olds and 26.1% of 12 to 17-year olds engaged in excessive screen time. Having a TV in their bedroom, for both groups, was strongly associated with excessive screen time. For the older age group, it was also strongly associated with obesity [42]. Excessive screen time on social media has negative impacts on sleep duration and/or sleep quality [41]. Adolescents in 2015 were 16–17% more likely to report sleeping less than 7 hours a night compared to those in 2009 [41]. Screen time, such as electronic device use, social media, and reading news online, rose during this time period [41]. This was linked with heightened odds of short sleep duration, with a clear exposure-response relationship for electronic devices after 2 or more hours of use per day [41]. Experimental studies show that limiting social media use to less than 30 minutes per day may lead to significant improvements in well-being (e.g., significant reduction in loneliness and depression) [38]. Symptoms of impaired self-care, emotional regulation, and social functioning are characteristic of MCI and ADRD [48]. Impairments in instrumental activities of daily living in adolescence and early adulthood that persist or worsen in middle adulthood could lead to diminished brain and cognitive-behavioural reserves increasing the risk of early onset dementia.

Studies show that early sociobiological embedding of stressors tends to have enduring lifetime effects rather than transient ones and increases the risk of lifetime physical and mental illness and social problems [103]. Brain structure and function, which is the most malleable during development, is continually remodeled by environmental factors and is particularly sensitive to acute and chronic stressors which exert their effects through the neuro-immuno-endocrine system [103]. Although neuroplastic changes in response to stressors may confer adaptive advantages in the short-term (allostasis), the persistence of changes that are abnormal and irreversible can be maladaptive later in life under accumulating pressures of the biopsychosocial environment (allostatic load and overload) [103]. Excessive screen time can act as both a non-normative stimulus, exerting its effects at a sub-stress threshold level, and as an acute and chronic stressor, increasing the risk of psychiatric problems during development and later in life [4]. Evidence is emerging that excessive social media use is a significant psychosocial stressor contributing to mental health problems in adolescents and young adults, for example, by lowering global self-esteem and heightening the risk of internet addiction, and increasing the prevalence of psychopathology including attentional, hyperactivity, anxiety, and depressive disorders [4]. Unlike offline face-to-face social connection, online virtual social interaction is associated with greater incidence of internalizing problems such as social anxiety and depression [4, 20]. Specifically, the association between screen time and depression was proposed and tested with three explanatory hypotheses: displacement, upward social comparison, and reinforcing spirals [17]. Upward social comparison suggests that the impact of screen time on mental health depends on the kind of content being viewed; for example, when individuals compare themselves with others who they consider are in more favorable positions (e.g., those with perfect bodies and lives) [17]. Reinforcing spirals also posits that screen time effects are mediated through content; however, reinforcing spirals adds that individuals try to obtain and choose information consistent with their thoughts which may then become increasingly negative in nature [17]. The displacement hypothesis suggests that all screen time adversely affects mental health because it displaces time one could be engaging in physical exercise and other healthy behaviours [17]. It was found that the upward social comparison and reinforcing spirals hypotheses explained associations between social media, television, and depression more than the displacement hypothesis [17]. Since those on social media platforms share the most idealized versions of themselves, it becomes commonplace for individuals to compare their real-life experiences with those of others who highlight positive moments, causing deleterious effects on self-esteem and life satisfaction [17]. Of the four types of screen use assessed (i.e., social media, TV viewing, video gaming, and computer use), only greater levels of social media and computer use were associated with depression, but not TV viewing or video gaming [17]. However, in a study on the relationship between screen time and psychological distress, internet addiction was associated with greater online video gaming and sexual activity, higher anxiety levels, and low email use [23]. Individuals with internet addiction also had increased avoidance coping mechanisms and higher rumination whilst having worsened self-care behaviors, such as seeking social support and getting adequate sleep [23]. Screen time potentially worsens- or in some cases creates- mental health problems which some speculate may lead to premature neurodegeneration and increased risk of premature cognitive decline in later adulthood [4].

Given the significant increases in average daily use of digital technology, we are concerned about the possibility of a rising trend in ADRD attributed to excessive screen time. To date, few studies have assessed the relationship between excessive screen time during development and ADRD, which is concerning because the ADRD burden is expected to at least double by 2060 [1]. The estimates provided in Matthews and colleagues (2019) [1] were from a nationally representative sample, ADRD was physician-diagnosed in a clinical setting, and sociodemographic characteristics (i.e., age, race, sex, and ethnicity) were included. We considered the same estimates as outlined in Matthews and colleagues [1] and also considered the effects of screen time and type, by age, and developmental stage. Statistical analyses by sex, race, or ethnicity were omitted because the data is not available or is not significant for these factors. Matthews and colleagues [1] also note that estimates did not include socioeconomic factors, such as education, which is a known risk factor in ADRD research [104]. To address this, our proposed hypothesis considered education attainment and IQ. Our report is the first to propose and explore the relationship between ADRD and screen time during development. Future research should consider additional factors, for example the serious short- and long-term implications of excessive screen time for the development of youth and young adult CBBR. These should include the short term implications of overall increased screen time from greater digital technology use both at home and at school (e.g., increased anxiety, depression, substance abuse, suicidal ideation and attempts etc.) and their long term consequences (e.g., permanent effects on brain development that will affect learning, memory and intelligence level, poorer school performance, greater risk of internalizing and externalizing psychological disorders, poorer overall health and economic outcomes, etc.). Future research should examine the lifelong implications of excessive screen time because it represents a significant proportion of daily activity during development, equal or greater than time spend on traditional educational activities (i.e., face-to-face instructional learning, reading from print, learning to hand write words and numbers). Additionally, physical activity should be included as a covariate because research shows that a reduction in physical activity is associated with increased screen time [105] and risk of developing ADRD [106, 107, 108].

While research on ADRD and screen time during development is limited, the current literature indicates that cognitive activity and physical activity are the two major modifiable risk factors for ADRD [106] and both cognitive and physical activity have also shown associations with screen time [109]. However, counterarguments on the evidence are mixed and inconclusive as to whether brain structure and physiology are associated with cognitive activity [106]. For example, cognitive activities may cross domains (i.e., completing a puzzle with a friend is both a cognitive activity and a social activity) and no such methods exist to classify the rate of cognitive activities (i.e., high cognitive activity versus a low cognitive activity), introducing noise into the variable [106]. Prospective research should continue to monitor the long-term effects of excessive screen time, including the ABCD study [33] that records the amount of screen use, amongst other factors, and the incidence of dementia in a large population in 2060. Preliminary results, for example in 2020 and 2040, could help inform future health policy decisions and potential preventative actions. Ideally research should focus on a number of factors including the influence of duration and type of media in order to inform appropriate guidelines and recommendations. A predicted effective approach would be to focus on informing the public on the dangers of excessive screen time use.