Browsing by Subject "vuorokausirytmi"

Aims of the study. The aim of this study was to examine normative development of sleep patterns and circadian rhythmicity during adolescence. Previous studies have found that sleep duration shortens across the lifespan, and especially adolescents’ sleep timing shifts later due to physiological and psychological factors. Sleep patterns in adolescence are connected to individual’s endogenous circadian rhythms, usually measured by delayed melatonin secretion in the evening. There is a lack of understanding how sleep patterns are related to circadian body temperature rhythms during adolescence. Methods. This study was part of SleepHelsinki! cohort study of the Sleep & Mind Research Group. Adolescents’ sleep patterns were measured with actigraphies, whereas circadian body temperature was measured from the skin surface. Circadian temperature rhythmicity was inspected by circadian period length, the mesor of skin surface temperature and the amplitude of daily changes within the rhythm. Baseline measurements were measured from 215 (71.6 % girls) adolescents aged 16–18 years. At one-year follow-up, 156 (76.3 % girls) adolescents were measured again. Mixed models for repeated measures were used to examine changes over the year in sleep patterns and endogenous circadian temperature rhythm, separately for both girls and boys. Sex differences were tested with one-way variance analysis. Linear and ordinal regressions were used to predict sleep and circadian rhythm over the year. Results and conclusions. Over the year, adolescents’ sleep duration became longer during the week, while weekend sleep shortened. However, this change was only significant for girls. Sleep schedule became more delayed for both girls and boys during the week, as sleep onset, midpoint and offset occurred at a later time. Circadian rhythm changed for boys, as their average skin surface temperature increased, and their circadian temperature amplitude became smaller. Boys also had significantly lower circadian temperature amplitude than girls at the follow-up. Compared to boys, girls were 5.85 times more likely to have a high circadian temperature amplitude at the follow-up measurement. Changes in sleep length during the week was moderated by temperature amplitude, with higher circadian amplitude predicting sleep duration to become longer. Still, the likelihood to have long sleep duration was affected by past sleep duration.

Objective. Despite the health benefits of physical exercise, several adolescents exercise less than recommended and physical activity decreases from childhood to adolescence. However, there has been quite little research into the factors affecting physical activity. The circadian rhythm shifts later in adolescence, which is linked to problems with schooling, as well as psychological and physical difficulties. However, further objective research is needed of the association of circadian rhythm and physical activity in adolescence. This study examined the association of circadian period length and timing of the circadian rhythm to physical activity in adolescents and whether sex moderates these associations. Methods. The sample consisted of 262 16–19 years old adolescents (70.6 % girls) who participated in the cohort study SleepHelsinki!. Circadian period length was measured by skin temperature and timing of the circadian rhythm was measured with an actigraphs according to the midpoint of sleep, as well as with the reduced version of the MEQ survey, which measures circadian preference. Metabolic equivalents as well as the amount of sedentary behavior, light physical activity and moderate to vigorous physical activity was calculated from the actigraphy data. Relationship between circadian period length and physical activity was analyzed with linear and quadratic regression analyzes, and relationship between midpoint of sleep and physical activity with linear regression analyzes. Relationship between circadian preference and physical activity was analyzed by one-way analyzes of variance. The moderating effect of gender was examined by adding the interaction of gender and independent variable to the models. Results. Circadian period length was in a quadratic relationship to light as well as moderate to vigorous physical activity: shorter and longer than average circadian period associated with lower activity level and a near-average circadian period with higher activity level. Later sleep midpoint associated with lower metabolic equivalent, lower light and moderate to vigorous physical activity and higher sedentary time. Circadian preference was not associated with physical activity. Gender did not moderate associations. Conclusions. Adolescents whose circadian rhythm is delayed or inconsistent with the rhythm of society should be considered when planning ways to support adolescent’s physical activity, because these adolescents are at greater risk for physical inactivity and its adverse health effects. One way could be shifting school start times later, which would reduce adolescent’s social jet lag, sleep deprivation and daytime fatigue, and thus support their physical activity.