Prevalence and Correlates of Meeting Sleep, Screen-Time, and Physical Activity Guidelines Among Adolescents in the United Kingdom

Abstract

This analysis of the UK Millennium Cohort Study examines the associations between sleep, physical activity, and screen time in adolescents aged 14 years in the United Kingdom.

There is convincing evidence that modifiable lifestyle behaviors, such as sleep, moderate to vigorous physical activity (MVPA), and screen time (ST), are associated with physical, social, and mental health outcomes in adolescents.¹ However, much of this evidence comes from studies examining behaviors independently. There is growing interest in the importance of combinations of these behaviors because of their potential synergistic effects on health.² To improve the health of adolescents, it is necessary to better understand the determinants of combinations of behaviors. There are few nationally representative data on the prevalence of meeting combinations of recommendations for sleep, ST, and MVPA,³ and little is known about the associated contextual factors.⁴

Methods

Data from members of the UK–representative Millennium Cohort Study, collected from January 2015 to March 2016, when the members were aged 14 years, were used.⁵ Sleep duration and ST were self-reported, and MVPA was assessed using the GENEActiv wrist-worn accelerometer (Activinsights Ltd) worn for 24 hours on a randomly selected week and weekend day (data were included if participants had ≥10 hours of valid wear for both days). A behavioral risk score of zero was applied when all recommendations were met (>8 hours of sleep on a school night, ST ≤2 hours per day, and MVPA ≥60 minutes/day⁶). The likelihood of having a behavioral risk score of zero was examined by logistical regression according to weighted household income, depressive symptoms, and obesity; these analyses were stratified by sex. Ethical approval was granted by the Northern and Yorkshire Multi-Centre Research Ethics Committee of the National Health Service. Written informed consent was received from parents or caregivers. Data analysis was completed with SPSS version 22 (IBM) from January to April 2019. All P values less than .05 were regarded as significant.

Results

Data from 3899 adolescents were included in the present analyses (of the 11 872 individuals for whom consent was on file at age 14 years [32.8%]). Excluded participants tended to be from lower socioeconomic strata (highest income level: included individuals, 885 [22.7%]; excluded individuals, 1547 [19.4%]; P = .001) and have higher prevalence of depressive symptoms (included individuals, 561 [14.4%]; excluded individuals, 1276 [16.0%]; P = .02) and obesity (included individuals, 257 [6.6%]; excluded individuals, 630 [7.9%]; P = .003), although differences were small. Overall, 378 adolescents (9.7%) met recommendations for sleep, ST, and MVPA concurrently; 3481 adolescents (89.3%) met guidelines for sleep, 1579 (40.5%) for MVPA, and 900 (23.1%) for ST; and 842 (21.6%) met guidelines for both sleep and ST, 1415 (36.3%) for both sleep and MVPA, and 409 (10.5%) for both ST and MVPA. Adolescent girls from the highest income tertile, compared with girls from the lowest, were more likely to meet all 3 recommendations (adjusted odds ratio [aOR], 2.13 [95% CI, 1.28-3.54]). Additionally, adolescent girls with depressive symptoms were less likely to meet all 3 recommendations (compared with those without depressive symptoms: aOR, 0.63 [95% CI, 0.41-0.96]) (Table). Adolescent boys who were obese (compared with those of normal body mass index; aOR, 0.39 [95% CI, 0.15-0.96]) and those with depressive symptoms (compared with those without depressive symptoms: aOR, 0.46 [95% CI, 0.21-1.00]) were less likely to meet all 3 recommendations (Table).

Table. Logistic Regression to Examine Factors Associated With Optimal Physical Behaviors, Stratified by Sex^a.

Characteristic	Adjusted Odds Ratio (95% CI)b
	Boys	Girls
Household income tertile
Lowest	1 [Reference]	1 [Reference]
Middle	0.62 (0.37-1.04)	1.34 (0.77-2.31)
Highest	1.09 (0.68-1.75)	2.13 (1.28-3.54)
International Obesity Task Force BMI groupc
Normal	1 [Reference]	1 [Reference]
Overweight	0.83 (0.54-1.28)	0.64 (0.42-0.99)
Obese	0.39 (0.15-0.96)	1.19 (0.68-2.10)
Depressive symptoms per the Mood and Feelings Questionnaire, points
<12	1 [Reference]	1 [Reference]
≥12	0.46 (0.21-1.00)	0.63 (0.41-0.96)

Abbreviation: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared).

^aBehavioral risk factor scores were calculated with participants scoring 1 point for each of the following risk factors: sleep of less than 8 hours on a school night; daily screen time of more than 2 hours; and device-measured moderate to vigorous physical activity of less than 60 minutes per day (derived from 5-second intervals in which the Euclidean norm minus one was more than 100 mg; 80% were longer than a 1-minute bout). Optimal physical behaviors are given a score of zero.

^bModels are mutually adjusted for all presented variables.

^cInternational Obesity Task Force cutoff values for normal, overweight, and obese BMIs are specific to age and sex and are therefore not presented numerically here.

Conclusions

Screen time was the main driver of not meeting all 3 recommendations, followed by MVPA and then sleep. Combinations of behavioral risk factors are highly prevalent among British adolescents, with only 9.7% meeting recommendations for sleep, ST, and MVPA. This value is higher than that reported in a study of US adolescents in which only 5% met all 3 recommendations,⁶ and it is marginally lower than that reported in a regional study of British children aged 9 to 11 years.³ Differences might be attributable in part to the older age of the US sample (16-17 years) and/or differences in methods used to assess the behaviors (ie, the use of devices to measure MVPA vs self-reports). Indeed, the physical activity recommendations were developed and established based on evidence from self-reported measures; thus using objective data to classify participants may result in discrepancies.

The first step toward targeted intervention efforts is an understanding of the factors that are associated with engaging in multiple unhealthy behaviors. Similarly to the US study, these analyses showed that adolescent boys and girls with depressive symptoms had lower odds of meeting all 3 recommendations, although associations of other independent variables, such as income and obesity, appeared to differ by sex in the present study.

Given that weight status and depression are socially patterned in the United Kingdom, the findings validate the need for UK-based prospective studies that use robust measures to understand associative pathways. It is also important to understand the socioeconomic patterning of lifestyle behaviors and health markers in girls and boys to inform interventions and policy.