IMPORTANCEChildren and adults spend large amounts of their leisure time using screen media, which may affect their health and behavior.OBJECTIVE To investigate the effect of reducing household recreational screen media use on physical activity and sleep in children and adults.DESIGN, SETTING, AND PARTICIPANTS This was a cluster randomized clinical trial with a 2-week follow-up. Enrollment began on June 6, 2019, and ended on March 30, 2021. This study included a population-based sample from 10 Danish municipalities. A total of 89 families (181 children and 164 adults) were recruited based on a population-based survey on screen media habits in families with children. To be eligible, the responding parent had to list self-reported recreational screen use greater than the 40th percentile of recreational screen time use in the source population (>2.4 hours per day). In addition, the parent had to be full-time employed (with no regular night shifts) or enrolled in full-time education.INTERVENTIONS Families were randomly assigned to the screen media reduction intervention (45 families, 86 children, 82 adults) designed to ensure participant compliance to a maximum use of screen media (Յ3 hours per week) for a 2-week period. Families randomly assigned to the control group (44 families, 95 children, 82 adults) were instructed to carry on as usual. MAIN OUTCOMES AND MEASURESThe primary outcome was between-group difference in leisure nonsedentary activity (in minutes per day) measured by combined thigh and waist accelerometry. Secondary outcomes included other physical activity and sleep parameters measured by single-channel electroencephalography. RESULTS Among the 89 randomized families (intervention group [45 families]: 86 children; mean [SD] age, 8.6 [2.7] years; 44 boys [51%]; 42 girls [49%]; control group [44 families]: 95 children, mean [SD] age, 9.5 [2.5] years; 38 boys [40%]; 57 girls [60%]), 157 children (87%) had complete data on the primary outcome. Eighty-three children (97%) in the intervention group were compliant to the screen use reduction during the intervention. The mean (SD) change in leisure nonsedentary activity in the intervention group was 44.8 (63.5) minutes per day and in the control group was 1.0 (55.1) minute per day (intention-to-treat between-group mean difference, 45.8 minutes per day; 95% CI, 27.9-63.6 minutes per day; P < .001). No significant between-group mean differences were observed between intervention and control for the electroencephalography-based sleep outcomes. CONCLUSIONS AND RELEVANCEIn this cluster randomized clinical trial, a recreational screen media reduction intervention resulted in a substantial increase in children's engagement in physical activity. The large effect size suggests that the high levels of recreational screen media use seen in many children should be a public health concern.

Objective Salivary cortisol and cortisone are used as biomarkers of physiological stress. Careful sampling of saliva for profiling of awakening response and the diurnal slope can be challenging in free-living environments, and validated sampling protocols are lacking. Therefore, we investigated (1) the level of compliance to a three-day home-based salivary sampling protocol, and (2) the within subject day-to-day variability of cortisol and cortisone outcomes and the required measuring days to obtain high reproducibility. Results Nineteen healthy adults (mean age: 42, 50% females) participated. Participants collected in total 434 salivary samples out of 456 scheduled (four samples per day over three consecutive days at two time points). We found high level of compliance to the proposed free-living salivary sampling protocol with 18 (95%) and 16 (84%) participants being compliant to numbers and timing of samples, respectively. The area under the curve for the morning salivary samples and peak-to-bed slope had moderate reproducibility for cortisol and cortisone (intraclass correlation coefficient: 0.51–0.68, and mean coefficient of variation: 14.7%-75.3%). Three-to-four measuring days were required for high reproducibility of the area under the curve for the morning salivary samples and peak-to-bed slope using this free-living salivary sampling protocol. Trial registration Clinical trial registered with www.clinicaltrials.gov (NCT03788525).

Aims: Little is known about the influence of parents’ screen media habits and attitudes towards screen media on children’s screen use. We investigated associations of parental screen use, their smartphone addiction and screen media attitudes, with children’s recreational screen use. Methods: This study was based on a population-based cross-sectional survey sent between May 2019 and November 2020 to a random sample of 6820 Danish parent–child dyads who answered questions regarding their screen media habits. Children were 6–11 years of age and had to reside with the parent. Multivariable adjusted regression analyses were conducted (in October 2021) separately for screen media use on weekdays and weekend days. Results: The analyses included 5437 parents (41.0 years, 67.6% girls) and 5437 children (8.9 years, 48.2% girls). The adjusted relative odds of excessive amounts of screen use of children (>3 hours/weekday and >4 hours/weekend day) was 5.8 (95% confidence interval (CI) 4.6; 7.3) on weekdays and 7.2 (95% CI 5.9; 8.8) on weekend days comparing the fourth and first quartile of parental screen use. Children of parents in the fourth quartile of parental screen use had 2.1 (95% CI 1.7; 2.5) and 2.5 (95% CI 2.2; 3.0) greater odds of screen use before bedtime on all week and weekend days, respectively. Children of parents who had a positive attitude towards their child’s screen use or were at high risk of smartphone addiction had significantly higher screen use and more frequent problematic screen use. Conclusions: Parent’s screen media habits and attitudes were strongly associated with their children’s recreational screen use.

Studies have linked higher digital screen use with poorer mental health. However, there is limited experimental evidence to suggest a causal relationship. In this trial, we aimed to investigate the effects of limiting recreational digital screen use on mental well-being, mood, and biomarkers of stress in healthy young and middle-aged adults. We randomly allocated 89 families (including 164 adults) to participate in an extensive screen media reduction intervention or control. Participants in the intervention group were instructed to decrease their recreational screen use to less than 3 hours/week/person. Intervention compliance was assessed using applications and tv-monitors. Overall subjective mental well-being and mood, and collected daily biomarkers of stress (salivary cortisol and cortisone) was assessed at baseline and 2-week follow-up. Reducing recreational digital screen use resulted in significantly improved self-reported well-being and mood in adults allocated to the intervention compared to control. We observed no intervention effects for biomarkers of stress. (ClinicalTrials.gov: NCT04098913, 23/09/2019).