Smartphone use health outcomes in children and adolescents: A systematic review of behavioral, developmental, and environmental risk pathways

Table 3 Effects of smartphone use on sleep outcomes by age group and study design

Ref.	Country	Age group	Sample size (n)	Study design	Exposure definition	Sleep outcomes	Key findings	Appraisal tool	Primary bias considerations	Overall risk
Kim et al[21], 2020	South Korea	5-8 years	Cohort (K-CURE)	Prospective cohort	Smartphone overuse (> 1 hour/day)	Total sleep time; Children’s Sleep Habits Questionnaire score; nocturnal awakening	Overuse group had shorter total sleep time (P < 0.05) and higher sleep problem scores, including more night awakenings	NOS	Strengths: Longitudinal design; part of a large prospective cohort (K-CURE). Limitations: Reliance on parental questionnaires for sleep assessment, which may introduce recall bias	Moderate
Lee et al[22], 2022	South Korea	4-7 years	314	4-year longitudinal study	Frequency of smartphone use	Sleep problems; bedtime resistance; sleep duration; daytime sleepiness	Smartphone use significantly predicted sleep problems (β = 0.328, P < 0.001); associated with shorter sleep and greater bedtime resistance	NOS	Strengths: Robust 4-year follow-up (2017-2020); utilized mixed-model analysis. Limitations: Sleep data were caregiver-reported via self-administered questionnaires	Moderate
Pickard et al[23], 2024	United Kingdom	16-30 months	105	Randomized clinical trial	Removal of screen use in hour before bedtime	Actigraphy-measured sleep efficiency; night awakenings	Screen removal improved sleep efficiency and reduced awakenings (small-moderate effect sizes)	RoB 2	Strengths: Assessor-blinded; objective sleep measurement via actigraphy; high retention (99%) and adherence (94%)	Low
Abid et al[24], 2024	Tunisia	Mean 9 years	13	Experimental (acute and repeated exposure)	90-minute nocturnal smartphone exposure	Total sleep time; waking after sleep onset; cognitive performance	Acute and repeated exposure reduced sleep time (-29 minutes to -47 minutes, P < 0.01); repeated exposure produced greater sleep disruption	RoB 2	Strengths: Objective measures (actigraphy, salivary cortisol, cognitive tests). Limitations: Extremely small sample size (n = 13), which limits statistical power and generalizability	Moderate to high
Foerster et al[27], 2019	Switzerland	7th-9th grade	843	Prospective cohort	Nocturnal awakenings due to phone; high screen time	Restless sleep; difficulty falling asleep	Nocturnal awakenings associated with new-onset restless sleep (OR = 5.66); high screen time linked to sleep onset problems	NOS	Strengths: Large sample (n = 843); controlled for relevant confounders using logistic regression. Limitations: Subjective reporting of nocturnal phone-related awakenings	Low to moderate
Nagata et al[25], 2023	United States	10-14 years	10280	Cross-sectional (ABCD study)	Bedtime screen behaviors; device in bedroom	Trouble falling/staying asleep; sleep disturbance	Device in bedroom increased sleep disturbance risk (RR = 1.27); bedtime streaming, texting, gaming associated with sleep problems	JBI	Strengths: National dataset with very large sample size (n = 10280); extensive control for socioeconomic and demographic variables. Limitations: Cross-sectional nature precludes causal inference	Low
Yoon et al[26], 2021	South Korea	Grade 4 and 7 (approximately 10-13 years)	4940	Cross-sectional panel analysis	Smartphone addiction subscales	Sleep duration	Addiction (tolerance subscale) associated with shorter sleep; gender moderated effect	JBI	Strengths: High sample size (n = 4940) from a national panel survey; used validated smartphone addiction sub-factors	Low
Rafique et al[28], 2020	Saudi Arabia	17-23 years	1925	Cross-sectional	≥ 8 hours/day use; ≥ 30 minutes after lights-off; phone near pillow	PSQI sleep quality; sleep latency; daytime sleepiness	High use and bedtime exposure associated with poor sleep quality and longer sleep latency	JBI	Strengths: Large sample size (n = 1925); used the validated PSQI. Limitations: Potential for social desirability bias in reporting screen time	Low to moderate
Tu et al[29], 2023	China	University students	152	Randomized longitudinal intervention	Restricting while-in-bed smartphone use	PSQI sleep quality; cognitive arousal	Restriction improved sleep quality; effect mediated by reduced pre-sleep cognitive arousal	RoB 2	Strengths: Longitudinal mediation analysis with a 4-week follow-up; significant focus on physiological mechanisms like cognitive arousal	Low

The following Risk of Bias assessment has been conducted: The Newcastle-Ottawa Scale for longitudinal/cohort studies, the Joanna Briggs Institute checklist for cross-sectional studies, and the Cochrane Risk of Bias framework for randomized trials and experimental designs. PSQI: Pittsburgh Sleep Quality Index; OR: Odds ratio; RR: Risk ratio; NOS: Newcastle-Ottawa Scale; JBI: Joanna Briggs Institute; RoB 2: Cochrane Risk of Bias.