Comportamento sedentário e marcadores cardiometabólicos em adolescentes: um estudo longitudinal

Abstract

Sedentary behaviour has been negatively associated with different cardiometabolic markers in adults. However, in adolescents, most studies used a cross-sectional design, did not consider possible confounding variables for analyses, and did not analyze the moderating effect. In addition, the results are inconclusive, mainly when the sedentary behaviour was measured by accelerometer. This study aimed to analyze the possible associations between time spent on sedentary behaviour and cardiometabolic markers in adolescents. This is a longitudinal study which analyzed the data from 294 adolescent enrolled at public school in the city of João Pessoa, state of Paraiba, Brazil, baseline (2014) and the first follow-up (2015) from the “Longitudinal Study of Sedentary Behavior, Physical Activity, Eating Habits and Health of Adolescents – LONCAAFS Study”. Sedentary behaviour was measured by the triaxial accelerometer (Actigraph GT3X+) and the cutoff point used was =100 counts/minutes. The total time of sedentary behaviour was estimated by minutes/day and the adolescents were categorized as “high” and “low” sedentary behaviour in 2014 and 2015 according to the cutoff of eight hours/day exposure to this behaviour. The cardiometabolic markers measured were fasting glucose, total cholesterol, plasma triglycerides, high (HDL-C) and low-density lipoproteins (LDL-C), body mass index, abdominal circumference, systolic and diastolic blood pressure. The score of cardiometabolic marker was obtained by the sum of the z scores of individual markers. The potential confounding factors tested were sociodemographic variables, hours of sleep, food intake, body mass index, light and moderate-vigorous physical activity. The moderator variables tested were moderate-vigorous physical activity and nutritional status. In each year, 60% of adolescents spent seven and nine hours/day on sedentary behavior (65.0% in 2014 and 63.3% in 2015) and there was an increase of 30 minutes/day from 2014 (mean = 7.5; sd = 1.8 hours) to 2015 (mean = 8.0, sd = 1.7 hours, p < 0.001). It was found that 22.5% of adolescents remained and 27.9% increased to more than eight hours/day of sedentary behaviour from 2014 to 2015. The longitudinal analysis showed a significant inverse relationship between total time spent in sedentary behavior and total cholesterol (ß = –0.098; 95%CI: – 0.173; –0.022) and LDL-C (ß = –0.091; 95%CI: –0.157; –0.026). It was found which nutritional status moderated the relationship between sedentary behaviour and diastolic blood pressure, and it was positively associated in obese adolescents (ß = 0.047; 95%CI: 0.010; 0.085). However, this relationship was not moderated by moderate-vigorous physical activity. Also, no significant differences were identified in the mean values of the cardiometabolic markers considering the "high" and "low" groups of sedentary behavior, according to the classification of physical activity and nutritional status. It was concluded that adolescents spend an excessive amount of time on sedentary behaviour per day, with a tendency to increase during follow-up. The exposure to sedentary time was not associated with cardiometabolic markers, except for the higher values of diastolic blood pressure presented among obese adolescents.

Sedentary behaviour has been negatively associated with different cardiometabolic markers in adults. However, in adolescents, most studies used a cross-sectional design, did not consider possible confounding variables for analyses, and did not analyze the moderating effect. In addition, the results are inconclusive, mainly when the sedentary behaviour was measured by accelerometer. This study aimed to analyze the possible associations between time spent on sedentary behaviour and cardiometabolic markers in adolescents. This is a longitudinal study which analyzed the data from 294 adolescent enrolled at public school in the city of João Pessoa, state of Paraiba, Brazil, baseline (2014) and the first follow-up (2015) from the “Longitudinal Study of Sedentary Behavior, Physical Activity, Eating Habits and Health of Adolescents – LONCAAFS Study”. Sedentary behaviour was measured by the triaxial accelerometer (Actigraph GT3X+) and the cutoff point used was =100 counts/minutes. The total time of sedentary behaviour was estimated by minutes/day and the adolescents were categorized as “high” and “low” sedentary behaviour in 2014 and 2015 according to the cutoff of eight hours/day exposure to this behaviour. The cardiometabolic markers measured were fasting glucose, total cholesterol, plasma triglycerides, high (HDL-C) and low-density lipoproteins (LDL-C), body mass index, abdominal circumference, systolic and diastolic blood pressure. The score of cardiometabolic marker was obtained by the sum of the z scores of individual markers. The potential confounding factors tested were sociodemographic variables, hours of sleep, food intake, body mass index, light and moderate-vigorous physical activity. The moderator variables tested were moderate-vigorous physical activity and nutritional status. In each year, 60% of adolescents spent seven and nine hours/day on sedentary behavior (65.0% in 2014 and 63.3% in 2015) and there was an increase of 30 minutes/day from 2014 (mean = 7.5; sd = 1.8 hours) to 2015 (mean = 8.0, sd = 1.7 hours, p < 0.001). It was found that 22.5% of adolescents remained and 27.9% increased to more than eight hours/day of sedentary behaviour from 2014 to 2015. The longitudinal analysis showed a significant inverse relationship between total time spent in sedentary behavior and total cholesterol (ß = –0.098; 95%CI: – 0.173; –0.022) and LDL-C (ß = –0.091; 95%CI: –0.157; –0.026). It was found which nutritional status moderated the relationship between sedentary behaviour and diastolic blood pressure, and it was positively associated in obese adolescents (ß = 0.047; 95%CI: 0.010; 0.085). However, this relationship was not moderated by moderate-vigorous physical activity. Also, no significant differences were identified in the mean values of the cardiometabolic markers considering the "high" and "low" groups of sedentary behavior, according to the classification of physical activity and nutritional status. It was concluded that adolescents spend an excessive amount of time on sedentary behaviour per day, with a tendency to increase during follow-up. The exposure to sedentary time was not associated with cardiometabolic markers, except for the higher values of diastolic blood pressure presented among obese adolescents.