Screen time is negatively associated with sleep quality and duration only in insufficiently active adolescents: A Brazilian cross-sectional school-based study

Influence of study shift on the interrelationships among chronobiological factors, health practices, and anthropometry in adolescents

The mismatch between chronobiological predispositions and social demands makes it difficult for adolescents with an evening chronotype to maintain healthy habits. This study aimed to explore the interrelationships among chronobiological factors, health practices, and anthropometry in adolescents attending morning and afternoon class shifts. In this cross-sectional study, 925 adolescents (14-19 years old) completed an online questionnaire covering food practices, chronotype, sleep duration, social jetlag, screen time, socioeconomic data, physical activity, school shift, and anthropometric measurements. The interrelationships among these variables were analyzed through structural equation modeling using six path models. Food practices were categorized into "complete meals" (breakfast, lunch, dinner, and bean consumption) - as healthy practices, "unhealthy foods" (sweets, fried snacks, soft drinks, salty ultra-processed foods, and fast food) and "vegetables and fruits," stratified by shift (morning or afternoon), with body mass index by age (BMI/age) as the main outcome. Among students in the morning shift, reduced sleep time was directly associated with increased BMI/age, while longer screen time was negatively associated with complete meal practices and physical activity. In the afternoon shift, a greater tendency towards an evening chronotype among adolescents was associated with reduced complete meal practices and lower regular fruit and vegetable consumption. Sleep duration was positively associated with a greater likelihood of a complete meal practices and regular fruit consumption. Moreover, longer screen time was positively associated with unhealthy food consumption. In both shifts, physically active adolescents consumed fruits more regularly. The practice of regular consumption of complete meals, fruits, vegetables, or unhealthy foods, in addition to being directly influenced by chronotype and other variables, was also influenced by shift. Adolescents with shorter sleep duration were at a higher risk of being overweight, suggesting a direct influence of sleep on anthropometric measurements. Our findings underscore the importance of considering study shifts in future interventions.

The Effect of Lockdown on Physiological Parameters of Sleep, Diet, Bowel Movement, Physical Activity, and Menstrual Cycle of Individuals Residing in Northeast India

Background Lockdown is a state of confinement that results in changes to the environmental factors that otherwise help entrain to circadian rhythm, and hence the need arises to understand the changes to various physiological factors during lockdown. Methodology A cross-sectional questionnaire-based study was conducted using snowball sampling, including people residing in Northeast India. A chi-square test was applied for the association between variables. A two-tailed Z test was done to analyze significant changes between two proportions. Result The final sample size was 992, and the mean age was 27.38 ± 10.887 years. A significant delay in bedtime (P = 0.0271), an increase in sleep latency (P = 0.0083), screen time duration (P = 0.0293), daytime sleep (P = 0.0155), and restfulness of sleep (P < 0.00001), as well as a decrease in sleep without awakening (P = 0.0001), were observed during lockdown compared to before the lockdown. In subjects sleeping beyond 1 AM, a significant decrease in restfulness (P = 0.00084) and an increase in sleep latency of more than one hour (P = 0.00528) were observed. An increase in water intake (508, 52%), fruit juice consumption (452, 46.1%), vegetable consumption (516, 52.9%), snacking (515, 52.8%), and body weight (447, 46.3%), along with a decrease in junk food consumption (527, 54.5%), were observed during lockdown. A significant decrease in alcohol consumption was observed during (P = 0.00338) and after (P = 0.03572) the lockdown. Breakfast timing was delayed in 395 individuals (40.5%), with a significant delay noted in those sleeping beyond 1 AM (P = 0.00634). A significant decrease in the frequency of lower stool passage (P = 0.01314) and a reduction in formed stools (P = 0.01016), along with a decrease in morning defecation (P = 0.0001), were observed. A significant decrease in morning defecation was observed in those sleeping beyond 1 AM (P = 0.01208). The changes in restfulness, sleep disturbance, screen time duration, sleep latency, defecation timing, and alcohol consumption observed during lockdown persisted even after the lockdown. Conclusions The most significant changes were seen for sleep. Changes in diet were inclined toward positive health. Sleeping beyond 1 AM, however, predisposed to longer latency of sleep, reduction in restfulness of sleep, and delayed breakfast and defecation time. Some of the changes observed during lockdown persisted even after the relaxation of restrictions.

Association of different domains of sedentary behavior and cardiovascular risk factors in adolescents: Cross-sectional study

BACKGROUND

Sedentary behavior (SB) has been related to cardiovascular risk factors (CVRF) such as high BMI, waist circumference (WC) and blood pressure (BP), including pediatric populations. However, it is still unclear whether the association between SB and CVRF could be domain dependent. Therefore, this study aimed to analyze the relationship between sedentary at different domains (time spent in TV, videogames, computer, smartphone) with CVRF in adolescents.

METHODS

A sample of 1011 adolescents (10-17 years old; 55.1% girls) was assessed. The different BS domains were obtained through a questionnaire, as well as socioeconomic status, habitual physical activity, smoking and alcohol consumption. BMI was calculated by objectively measured height and body mass, WC was assessed at middle point between the last rib and iliac crest, and BP was assessed by a digital oscillometric device. The relationship between SB and CVRF was determined by quantile regression, adjusted for sex, age, socioeconomic status, physical activity, smoking and alcohol consumption.

RESULTS

Elevated time in smartphone use was associated with higher median values of WC (β=1.88; 95%CI: (0.27; 3.49) and SBP (β=2.70; 95%CI: 0.35; 5.05). High total time spent in SB was associated with higher median values of BMI (β=0.68; 95%CI=(0.02; 1.35), WC (β=1.95; 95%=0.47; 3.42) and SBP (β=2.52; 95%CI: 0.37; 4.68).

CONCLUSIONS

Smartphone use and total SB time were related to higher CVRF in adolescents. Cardiovascular health promotion strategies should focus on reducing SB in pediatric populations, especially smartphone use.