Adolescent mental health and cardiorespiratory fitness: A comparison of two cohorts 12 years apart.

The aim of the study was to compare the mental health and cardiorespiratory fitness (CRF) of adolescents in two cross-sectional cohorts, one measured in 2003 and the other in 2015, both at age 15 and across sexes. The study also sought to estimate the association between mental health and CRF in the two cohorts and examine the relationship between the level of CRF and mental health in each cohort overall and by sex. Data from 443 participants born in 1988 (228 males, 215 females) and 303 participants born in 1999 (126 males, 177 females) were analyzed. Mental health was assessed using self-reports of body image, self-esteem, and symptoms of depression and anxiety. CRF was estimated using a maximal cycle ergometer test. From 2003 to 2015, body image scores improved (p = .043), self-esteem remained stable, and CRF declined significantly (p < .001). No self-esteem differences were observed between sexes in any cohort. Males had higher CRF and body image scores than females in both cohorts (p < .001 for all comparisons). Higher CRF correlated with fewer depressive symptoms across sexes and cohorts. Specifically, higher CRF was associated with anxiety in females and improved body image in males (2003) and both sexes (2015). Increased CRF was linked to higher self-esteem in females but not in males. Overall, higher CRF levels were associated with better mental health outcomes for both sexes. These results highlight the potential of improving adolescent mental health through increased physical fitness.

Longitudinal development and tracking of cardiorespiratory fitness from childhood to adolescence.

BACKGROUND: Cardiorespiratory fitness (CRF) is an important indicator of health in childhood and adolescence but longitudinal studies on the development and tracking of CRF from childhood to adolescence are scarce. OBJECTIVES: The objectives of this study were (1) to assess longitudinal development and track CRF over 10 years from childhood to adolescence, and (2) to examine potential sex differences in the development and tracking of CRF during this period. METHODS: Participants were Icelandic children born in 1999, measured at the age of 7 (n = 190, 106 girls), 9 (n = 163, 95 girls), 15 (n = 239, 134 girls), and 17 (n = 202, 119 girls). CRF was assessed with a maximal cycle ergometer test and expressed as maximal power output (Max W) and maximal power output relative to lean mass (W/kgLM). Multilevel regression models were used to study the longitudinal development of CRF, and tracking was assessed with Spearman's rank correlation, logistic regression, and the percentage of participants remaining in low, moderate, or high CRF categories between measurements. RESULTS: Max W and W/kgLM increased for both boys and girls up to age 15. Max W plateaued for both boys and girls while W/kgLM plateaued for girls but declined for boys from age 15 to 17. Boys had higher Max W than girls from age 15 and higher W/kgLM from age 9. CRF tracked at low to moderate levels from childhood to adolescence and at high levels in adolescence, with higher values observed for boys than girls. CONCLUSIONS: Age 15 was a critical time point in the development of CRF, with values starting to plateau for girls and decline for boys. The results support early intervention for improved CRF in later years, with interventions targeting all children, regardless of their CRF level.

Changes in health-related lifestyle choices of university students before and during the COVID-19 pandemic: Associations between food choices, physical activity and health.

The COVID-19 pandemic has had a profound effect on our lives and society, influencing both individuals' lifestyles and habits. Recent research shows that anxiety and loneliness have continued to rise, along with changes in food and lifestyle choices. The aim of the study was to investigate whether the pandemic influenced food choices and consumption of energy drinks, alcohol, fruits, and vegetables among first-year university students. Additionally, assessing the relationship between mental and physical health, physical activity, and food choices. A total of 128 male and 128 female first-year students at the University of Iceland were invited to answer an electronic questionnaire in January and early February 2021. A total of 118 students (54% men) participated in the study and valid answers were 115 (46% participation rate). Almost half of the students (44%) experienced that their food choices had worsened, while 14% reported an improvement, compared to before the pandemic. Consumption of caffeinated beverages increased for 26% of students, while 19% experienced a decrease. Just over half of the students reported not drinking alcohol (13%) or reduced consumption (41%). Participants who reported that their mental health had deteriorated or remained the same tended to spend less time on physical activity and experienced worsened food choices (p<0.05). Similarly, those who spent less or the same time on physical activity estimated that their food choices had deteriorated (p<0.05). The COVID-19 pandemic has had a significant impact on the lifestyles of university students and this study has revealed how lifestyle choices and mental health seem to be highly affected by one another. Additionally, the potentially harmful effects of excessive intake of energy drinks need to be enhanced. Interestingly, about 40% of the respondents in the current study drank less alcohol during the pandemic than prior to the pandemic, indicating a strong relationship between alcohol drinking and social gatherings. This study reveals the importance of educating young people on healthy lifestyle choices and the importance of mental health needs to be emphasised.

The relationship between online communication and adolescents' mental health: Long-term evaluation between genders.

AIMS: In a relatively short time, online communication has become an important part of adolescents' lives, and concerns have been raised about its potential effects on mental health. The first aim was to compare mental health status and online communication in 15-year-old Icelanders born in 1988 and in 1994. The second aim was to assess whether the relationship between online communication and mental health has changed among 15-year-old Icelanders from 2003 to 2015 across genders. METHODS: Analysis used data from self-reports from 2003 (N=385, 51% males) and 2015 (N=302, 42% males). Mental health was assessed with subscales of Symptom Checklist 90 and online communications with self-reports. To evaluate the difference in anxiety and depression, a factorial analysis of variance was conducted between gender and years. Multigroup structural equation modelling was used to assess the change in the relationship between years. RESULTS: Symptoms of anxiety and depression remained unchanged for males. Symptoms of depression increased for females, while anxiety was stable between 2003 and 2015. In 2003, there was no relationship between online communication and mental health. However, in 2015, an association was found for females. CONCLUSIONS: Depression is getting worse for adolescent females, and an association between time spent online communicating and mental health emerged for them in 2015, which did not exist in 2003. These findings add to the possibility that online communication is harmful for mental health, but more detailed studies are still needed.

Screen Time and Body Image in Icelandic Adolescents: Sex-Specific Cross-Sectional and Longitudinal Associations.

Studies of adolescent body image and screen use are mostly limited to girls, and longitudinal data are scarce. We examined cross-sectional and longitudinal associations between these variables in mid-adolescent boys and girls. Data was collected when participants were at age 15 and 17, by questionnaire and objective measurements (n = 152 had complete data). Sex-specific linear regression was used to explore cross-sectional and longitudinal associations of self-reported screen use (total use, and time spent in gaming, TV/DVD/internet-based watching and internet use for communication) and body image, adjusting for vigorous physical activity, symptoms of depression, and body composition. Screen time was negatively associated with body image at both time points, although more strongly at age 15, and for girls only. Gaming and TV/DVD/internet watching was more strongly associated with body image than internet use for communication. Girls with above median screen time at both ages had 14% lower body image score at age 17 than girls with below median screen time at both time points. Our results suggest that screen use is likely to play a role in the development of body dissatisfaction among adolescent females. Limiting screen time may, therefore, help to mitigate body dissatisfaction in adolescent girls.

Sleep timing and consistency are associated with the standardised test performance of Icelandic adolescents.

Sleep has been shown to affect cognitive function in laboratory studies; however, its association to the academic performance of adolescents has largely been demonstrated using self-reported measures. Studies with objective measures of both sleep and academic performance are limited. The aim of the present study was to determine whether the free-living sleep quantity, quality, and timing of 15-year-old adolescents measured with wrist actiography are associated with their scores on national standardised examinations as an objective measure of academic achievement. We measured sleep with wrist actiography for 1 week in 253 (150 girls) Icelandic adolescents with a mean (SD) age of 15.9 (0.3) years. Multiple linear regression was used to assess associations between sleep parameters and combined standardised examination scores in mathematics, English, and Icelandic obtained from the Icelandic Directorate of Education. We found that students went to bed at 00:49 hours (± 51.8 min) and slept for a mean (SD) of 6.6 (0.7) hr/night, with a median (interquartile range) night-to-night variation in sleep duration of 1.2 (0.7) hr and an efficiency of 88.1 (5.3)%. Combined analyses adjusted for sex, demonstrated that both bedtime and night-to-night variability in total sleep time were negatively associated with the average score across all topics. Sex-specific associations did not indicate clear differences between boys and girls. These findings suggest that, in addition to appropriate sleep duration, public health guidance should also highlight the importance of early and consistent sleep schedules to academic achievement for both boys and girls.

Health and well-being of university students before and during COVID-19 pandemic: A gender comparison.

OBJECTIVE: COVID-19 has affected people's health in various ways. University students are a particularly sensitive group for mental and physical health issues. The aim of this study was to assess and compare the mental and physical health of male and female first-year university students during and before COVID-19. METHOD: Total of 115 first-year university students (54% male) answered questions about mental and physical health. The students were asked to estimate their physical activity, sedentary behavior, loneliness, stress, and sleep quality during COVID-19 opposed to before the pandemic. RESULT: Males had fewer symptoms of anxiety and depression, and their self-esteem was higher than females (p<0.05). Over 50% of both genders estimated their mental health to be worse than before COVID-19. Larger proportion of males (69%) compared to females (38%) estimated that their physical health had worsened than before the pandemic. Larger proportion of females (38%) than males (14%) experience increased loneliness and stress (68% vs. 48%). Over 70% of both genders estimated increased sedentary behavior than before the pandemic, and larger proportion of males (76%), compared to females (56%), estimated that they were less physically active than before COVID-19. About 50% of participants estimated their sleep quality was worse than before COVID-19. CONCLUSION: University students estimated their mental and physical health to have deteriorated during the pandemic. Therefore, it is important that the school and healthcare systems assist students in unwinding these negative health and lifestyle changes that have accompanied the pandemic.

Organized Sport Participation, Physical Activity, Sleep and Screen Time in 16-Year-Old Adolescents.

This study aimed to examine the association of different frequencies of organized sport participation (OSP) with physical activity, cardiorespiratory fitness, body composition, sleep, and screen time among adolescents. A cross-sectional study involving 315 16-year-old adolescents was conducted. OSP was self-reported, being categorized as 0 times a week, less than three times a week, 4-5 times a week, and 6-7 times a week, on average. Screen time was also self-reported but physical activity and sleep duration were objectively measured. Cardiorespiratory fitness and body composition were measured using a maximal cycle ergometer test and a dual-energy X-ray absorptiometry (DXA) scan, respectively. An analysis of covariance revealed a significant association between OSP and physical activity (F (3, 286) = 14.53, p < 0.01), cardiorespiratory fitness (F (3, 236) = 17.64, p < 0.01), screen time (F (3, 294) = 8.14, p < 0.01), body fat percentage (F (3, 292) = 11.84, p < 0.01), and fat free mass (F (3, 290) = 5.76, p < 0.01. No significant association was found between OSP and sleep duration. Post hoc analyses showed that OSP at least four times a week was beneficial to favorable physical activity levels, cardiorespiratory fitness, screen time, and body composition and may therefore serve as a valuable tool in battling unhealthy lifestyle behaviors among adolescents.

Association between free-living sleep and memory and attention in healthy adolescents.

In laboratory studies, imposed sleep restriction consistently reduces cognitive performance. However, the association between objectively measured, free-living sleep and cognitive function has not been studied in older adolescents. To address this gap, we measured one week of sleep with a wrist-worn GT3X+ actigraph in 160 adolescents (96 girls, 17.7 ± 0.3 years) followed by assessment of working memory with an n-back task and visual attention with a Posner cue-target task. Over the week, participants spent 7.1 ± 0.8 h/night in bed and slept 6.2 ± 0.8 h/night with 88.5 ± 4.8% efficiency and considerable intra-participant night-to-night variation, with a standard deviation in sleep duration of 1.2 ± 0.7 h. Sleep measures the night before cognitive testing were similar to weekly averages. Time in bed the night before cognitive testing was negatively associated with response times during the most challenging memory task (3-back; p = 0.005). However, sleep measures the night before did not correlate with performance on the attention task and weekly sleep parameters were not associated with either cognitive task. Our data suggests shorter acute free-living sleep may negatively impact difficult memory tasks, however the relationship between free-living sleep and cognitive task performance in healthy adolescents is less clear than that of laboratory findings, perhaps due to high night-to-night sleep variation.

Changes in sleep and activity from age 15 to 17 in students with traditional and college-style school schedules.

OBJECTIVES: Sleep duration and physical activity decline with age during adolescence. Earlier school schedules may contribute to these declines. The aim of this longitudinal study was to track changes in sleep and activity of Icelandic youth from primary to secondary school and compare students who enrolled in secondary schools with traditional and college-style schedules. METHODS: We measured free-living sleep and activity with wrist actigraphy and body composition by dual-energy x-ray absorptiometry in 145 students at age 15 and age 17, when 58% attended schools with college-style scheduling. Differences from 15 to 17 and between students of different school structures were assessed with mixed-effect models. RESULTS: Actigraphs were worn for 7.1 ± 0.4 nights at 15 and 6.9 ± 0.4 nights at 17. Overall, sleep duration decreased from 6.6 ± 0.7 h/night to 6.2 ± 0.7 h/night from age 15 to 17 (P < .001). Students with traditional schedules reduced school-night sleep duration 26 min/night at follow-up (P< .001), while sleep duration did not change for college-style students. All students went to bed later on school nights at follow-up, but only college-style students rose later. Sleep efficiency and awakenings did not differ by schedule-type. Neither sex changed body fat percentage, but average school-day activity decreased by 19% (P< .001) on follow-up and did not differ by schedule-type. CONCLUSIONS: Over the 2-year period, adolescents decreased weekly sleep duration and activity, but only those continuing traditional schedules reduced school-night sleep. This suggests greater individual control of school schedule may preserve sleep duration in this age group, which may be beneficial during the transition into adulthood.

Less physical activity and more varied and disrupted sleep is associated with a less favorable metabolic profile in adolescents.

BACKGROUND: Sleep and physical activity are modifiable behaviors that play an important role in preventing overweight, obesity, and metabolic health problems. Studies of the association between concurrent objective measures of sleep, physical activity, and metabolic risk factors among adolescents are limited. OBJECTIVE: The aim of the study was to examine the association between metabolic risk factors and objectively measured school day physical activity and sleep duration, quality, onset, and variability in adolescents. MATERIALS AND METHODS: We measured one school week of free-living sleep and physical activity with wrist actigraphy in 252 adolescents (146 girls), aged 15.8±0.3 years. Metabolic risk factors included body mass index, waist circumference, total body and trunk fat percentage, resting blood pressure, and fasting glucose and insulin levels. Multiple linear regression adjusted for sex, parental education, and day length was used to assess associations between metabolic risk factors and sleep and activity parameters. RESULTS: On average, participants went to bed at 00:22±0.88 hours and slept 6.2±0.7 hours/night, with 0.83±0.36 hours of awakenings/night. However, night-to-night variability in sleep duration was considerable (mean ± interquartile range) 0.75±0.55 hours) and bedtime (0.64±0.53 hours) respectively. Neither average sleep duration nor mean bedtime was associated with any metabolic risk factors. However, greater night-to-night variability in sleep duration and bedtime was associated with higher total body and trunk fat percentage, and less physical activity was associated with higher trunk fat percentage and insulin levels. CONCLUSION: Greater nightly variation in sleep duration and in bedtime and less physical activity were associated with a less favorable metabolic profile in adolescents. These findings support the idea that, along with an adequate amount of physical activity, a regular sleep schedule is important for the metabolic health of adolescents.

[Vitamin D status of Icelandic children and youngsters: Longitudinal study]. / D-vítamínbúskapur íslenskra barna og ungmenna. Langtímarannsókn

OBJECTIVE: Vitamin D plays a key role for children's growth and physical developement, not only by promoting bone health but also by its influence on extraskeletal systems. The Icelandic Directorate of Health recommends a vitamin D concentration in blood of at least 50 nmol/l. The object of this study was to evaluate the vitamin D status of Icelandic children and youngsters at four different ages, and furthermore to evaluate changes in vitamin D concentrations over time and connection to parathyroid hormone status (S-PTH). MATERIAL AND METHODS: The subjects were students from six elemen-tary schools in Reykjavík, born in 1999. Blood tests were taken four times, in 2006, 2008, 2015 og 2017. Some of the subjects took part in all four tests, but more students joined in 2015 and 2017. RESULTS: In all the tests, around 60% of the subjects had lower vitamin D concentrations than recommended by The Icelandic Directorate of Health. Only 13% met the recommended criteria of a concentration over 50 nmol/l in repeated tests and 38.9% of the subjects had lower concentrations than recommended in at least two tests. There was no significant difference between sexes except that 17 year old girls had significantly higher Vitamin D concentrations than boys (p=0.04). S-PTH was negatively correlated to vitamin D concentrations at ages 7, 15 and 17 but there was not a significant correlation at age 9. S-PTH values were lowest at age 7 and then increased with age. CONCLUSION: The majority of Icelandic children and youngsters have vitamin D concentrations under the values recommended by The Icelandic Directorate of Health. In many cases, the concentrations are repeatedly too low. It is clear that there is a need for increased vitamin D intake within this group if the goal regarding recommended concentrations is to be achieved. However, the influence of vitamin D deficiency on public health is not fully known.

Less screen time and more physical activity is associated with more stable sleep patterns among Icelandic adolescents.

OBJECTIVES: Emerging evidence suggests that inconsistent sleep may affect physical and psychological health. Thus, it is important to identify modifiable determinants of sleep variability. Screen time and physical activity are both thought to affect sleep, but studies of their relationship to sleep variability using objective measures are lacking. We examined cross-sectional associations between these variables in mid-teen adolescents using objectively measured sleep and activity. METHODS: Wrist-worn accelerometers were used to measure one week of sleep and activity in 315 tenth grade students (mean age 15.8y) from six Reykjavík compulsory schools. Participants reported their daily hours of screen time. Regression analysis was used to explore associations of screen time and physical activity with variability in duration, quality, and timing of sleep, adjusting for DXA-measured body fat percentage, parental education, and physical activity or screen time. RESULTS: Screen time, especially game playing, was associated with variability in duration, timing, and quality of sleep, most strongly with variation in bedtime. Physical activity was inversely associated with variability in duration, timing, and quality of sleep, most strongly with variation in the number of awakenings. Boys had less stable sleep patterns and higher screen time than girls, and sex-specific associations of screen time with sleep variability parameters were significant for boys only. CONCLUSIONS: Less screen time and more physical activity were independently associated with less sleep variability among mid-teen adolescents. Our results indicate that encouraging youngsters toward an active lifestyle with limited screen use may be important to achieve more consistent sleep.

[Fitness, body composition and quality of life following cancer treatment]. / Þrek, holdafar og heilsutengd lífsgæði eftir krabbameinsaðgerð

INTRODUCTION: Five-year survival of people diagnosed with cancer has increased in past decades. Knowledge of the long-term effects of cancer treatment on fitness, body composition and health related quality of life (HR-QoL) is important for cancer patients. The study aimed to evaluate body composition, HR-QoL and personality D of people post cancer treatment in the last 10 years; and to observe whether fitness was correlated with body composition and HR-QoL amongst them. MATERIAL AND METHODS: Eighty participants 25 - 77 y/o of both genders in remission from cancer answered questionnaires on HR-QoL (SF-36v2 and EQ-5D-3L), personality D (DS14), general health, lifestyle and cancer treatment. Participants had their blood pressure measured, conducted the 6-minute walk test (6MWT) and had their body composition meas-ured: body mass index, body fat percentage, waist and hip circumferences. SPSS was used for statistical analysis. RESULTS: Approximately 2/3 of the participants had body composition over recommended values. Over half were overweight or obese. 66.3% had waist circumference over recommended values and 45.0% had waist/hip ratio over recommended values. 6MWT average distance was 634 m +/- 83 m. Significant correlation (p<0.05) was found between 6MWT and body composition and most categories of HR-QoL. -Increased fitness correlated with better body composition and higher HR-QoL. Only 13.8% of participants showed personality D. CONCLUSION: Cancer survivor's body composition is generally not at its best. It is important that people diagnosed with cancer are informed on the importance of healthy body composition. Fitness is an indicator for HR-QoL and body composition of cancer survivors.

Longitudinal Change in Adolescent Bedtimes Measured by Self-Report and Actigraphy.

INTRODUCTION: Sleep is often quantified using self-report or actigraphy. Self-report is practical and less technically challenging, but prone to bias. We sought to determine whether these methods have comparable sensitivity to measure longitudinal changes in adolescent bedtimes. METHODS: We measured one week of free-living sleep with wrist actigraphy and usual bedtime on school nights and non-school nights with self-report questionnaire in 144 students at 15 y and 17 y. RESULTS: Self-reported and actigraphy-measured bedtimes were correlated with one another at 15 y and 17 y (p < .001), but reported bedtime was consistently earlier (>30 minutes, p < .001) and with wide inter-method confidence intervals (> ±106 minutes). Mean inter-method discrepancy did not differ on school nights at 15 y and 17 y but was greater at 17 y on non-school nights (p = .002). Inter-method discrepancy at 15 y was not correlated to that at 17 y. Mean change in self-reported school night bedtime from 15 y to 17 y did not differ from that by actigraphy, but self-reported bedtime changed less on non-school nights (p = .002). Two-year changes in self-reported bedtime did not correlate with changes measured by actigraphy. CONCLUSIONS: Although methods were correlated, consistently earlier self-reported bedtime suggests report-bias. More varied non-school night bedtimes challenge the accuracy of self-report and actigraphy, reducing sensitivity to change. On school nights, the methods did not differ in group-level sensitivity to changes in bedtime. However, lack of correlation between bedtime changes by each method suggests sensitivity to individual-level change was different. Methodological differences in sensitivity to individual- and group-level change should be considered in longitudinal studies of adolescent sleep patterns.

Dynamic sitting: Measurement and associations with metabolic health.

Dynamic sitting, such as fidgeting and desk work, might be associated with health, but remains difficult to identify out of accelerometry data. We examined, in a laboratory study, whether dynamic sitting can be identified out of triaxial activity counts. Among 18 participants (56% men, 27.3 ± 6.5 years), up to 236 counts per minute were recorded in the anteroposterior and mediolateral axes during dynamic sitting using a hip-worn accelerometer. Subsequently, we examined in 621 participants (38% men, 80.0 ± 4.7 years) from the AGES-Reykjavik Study whether dynamic sitting was associated with cardio-metabolic health. Compared to participants who recorded the fewest dynamic sitting minutes (Q1), those with more dynamic sitting minutes had a lower BMI (Q2 = -1.39 (95%CI = -2.33;-0.46); Q3 = -1.87 (-2.82;-0.92); Q4 = -3.38 (-4.32;-2.45)), a smaller waist circumference (Q2 = -2.95 (-5.44;-0.46); Q3 = -3.47 (-6.01;-0.93); Q4 = -8.21 (-10.72;-5.71)), and a lower odds for the metabolic syndrome (Q2 = 0.74 [0.45;1.20] Q3 = 0.58 [0.36;0.95]; Q4 = 0.36 [0.22;0.59]). Our findings suggest that dynamic sitting might be identified using accelerometry and that this behaviour was associated with health. This might be important given the large amounts of time people spend sitting. Future studies with a focus on validation, causation and physiological pathways are needed to further examine the possible relevance of dynamic sitting.

Above average increases in body fat from 9 to 15 years of age had a negative impact on academic performance, independent of physical activity.

AIM: The associations between body fat levels and physical activity with academic performance are inconclusive and were explored using longitudinal data. METHODS: We enrolled 134/242 adolescents aged 15, who were studied at the age of nine and agreed to be followed up from April to May 2015 for the Health behaviours of Icelandic youth study. Accelerometers measured physical activity, body mass indexes (BMI) were calculated and dual-energy X-ray absorptiometry scans assessed the participants' body composition at nine and 15. Their language and maths skills were compared to a growth model that estimated the academic performances of children born in 1999. RESULTS: Higher than normal body fat levels between the ages of nine and 15 were negatively associated with maths performance, but the same association was not found for Icelandic language studies. These were Pearson's r = -0.24 (p = 0.01) for BMI and Pearson's r = -0.34 (p = 0.01) for the percentage of body fat. No associations were found with changes in physical activity. CONCLUSION: Children who put on more body fat than normal between the ages of nine and 15 had an increased risk of adverse academic performance that was independent of changes in physical activity.

Different cardiorespiratory fitness expressions based on the maximal cycle ergometer test show no effect on the relation of cardiorespiratory fitness to the academic achievement of nine-year-olds.

The relationship between cardiorespiratory fitness and academic achievement has been inconclusive. The results may depend on how cardiorespiratory fitness is expressed. The aim of this study is to explore the impact of different cardiorespiratory fitness expression methods, measured by the maximal cycle ergometer test, on the relationship between cardiorespiratory fitness and academic achievement. A cross-sectional study consisting of 303 Icelandic 4th grade students (163 girls) was conducted. Cardiorespiratory fitness was assessed using a graded maximal cycle ergometer test and scores of standardized tests in Icelandic and math obtained from the Icelandic National Examination Institute. Cardiorespiratory fitness was measured as absolute power output in watts in a maximal progressive cycle ergometer test. To adjust for different body sizes, the power output was scaled to body weight, body height, body surface area, and allometrically expressed body weight. In addition, linear regression scaling was also used to adjust for different body sizes. No significant relationship was found between any of the cardiorespiratory fitness expressions and academic achievement, using both univariate and multivariate linear regression analyses. The use of different methods to express cardiorespiratory fitness does not significantly affect the association with the academic achievement of fourth grade students.

Less screen time and more frequent vigorous physical activity is associated with lower risk of reporting negative mental health symptoms among Icelandic adolescents.

OBJECTIVE: Few studies have explored the potential interrelated associations of screen time and physical activity with mental health in youth, particularly using objective methods. We examined cross-sectional associations of these variables among Icelandic adolescents, using objective and subjective measurements of physical activity. METHODS: Data were collected in the spring of 2015 from 315 tenth grade students (mean age 15.8 years) in six elementary schools in metropolitan Reykjavík, Iceland. Participants reported, via questionnaire, on demographics, weekly frequency of vigorous physical activity, daily hours of screen time and mental health status (symptoms of depression, anxiety and somatic complaints, self-esteem and life satisfaction). Total physical activity was measured over one week with wrist-worn accelerometers. Body composition was determined by DXA-scanning. Poisson regression analysis was used to explore independent and interactive associations of screen time and physical activity with mental health variables, adjusting for gender, body fat percentage and maternal education. RESULTS: Less screen time (below the group median of 5.3 h/day) and more frequent vigorous physical activity (≥4x/week) were each associated with reporting fewer symptoms of depression, anxiety, low self-esteem, and life dissatisfaction. No significant associations were observed between objectively measured physical activity and mental health outcomes. Interactive regression analysis showed that the group reporting both less screen time and more frequent vigorous physical activity had the lowest risk of reporting symptoms of depression, anxiety, low self-esteem, and life dissatisfaction. CONCLUSIONS: Reports of less screen time and more frequent vigorous physical activity were associated with lower risk of reporting mental health problems among Icelandic adolescents. Those who reported a combination of engaging in less screen time and more frequent vigorous physical activity had the lowest risk, suggesting a synergistic relationship between the two behaviors on mental health outcomes. Our results support guiding youth towards more active and less sedentary/screen-based lifestyle.

[Physical activity and sleep in Icelandic adolescents].

INTRODUCTION: Physical activity and sleep are major determinants of overall health. According to international recommendations, adolescents should engage in moderate to vigorous physical activity for at least 60 min each day and sleep eight to ten hours each night. The association between physical activity and sleep in adolescents is not well known. The aim of the study was to estimate a) the proportion of Icelandic adolescents that achieves recommended physical activity and sleep, b) if there is an association between physical activity and sleep patterns, and c) sex differences in physical activity and sleep. MATERIAL AND METHODS: A total of 411 adolescents from the 10th grade in six schools in Reykjavik were invited to participate in a cross-sectional study in the spring of 2015. Valid data was obtained from 106 boys and 160 girls. Objective and subjective measures of physical activity and sleep were made by wrist-worn accelerometers and a questionnaire. RESULTS: Almost half of the participants fulfilled the physical activity recommendations according to the questionnaire. Although 51.1% reported usually getting enough sleep, only 22.9% achieved the recommended sleep length according to objective assessment. No associations were observed between sleep and subjective physical activity. Girls had higher accelerometer-measured physical activity than boys on non-school days (p<0.01), but weekly averages were not different between sexes. Girls and boys did not differ in subjective or objective measures of sleep. CONCLUSION: The behavior of Icelandic adolescents does not reflect recommended amount of sleep and physical activity. Only 22.9% obtained the recommended sleep length and just 11.3% fulfilled recommendations of both sleep and physical activity.