Aspectos cronobiológicos de la obesidad infantilrelación con horarios de comida, actividad física y luz

Abstract

Circadian health assessment has been limited to the adult population. Childhood chronobiology studies have begun to emerge, but there are still very few that address this field and investigations of school-age children are still scarce. Therefore, our objectives were: 1) To develop a circadian score that, by combining non-invasive tools, is capable to detect the circadian function in school-age children and to explore circadian differences between boys and girls and with a sample of adults. 2) To assess the use of saliva as a non-invasive tool for the determination of inflammatory biomarkers that allows us to detect the metabolic changes associated with BMI, dietary characteristics and physical activity. 3) To evaluate the child's chronotype using objective circadian-tools and to study its possible relationship with social jet lag, exposure to light at night, sleep disturbances, academic score and metabolic risk. 4) To find out if dinner timing influences obesity and child's cardiometabolic health. 5) To study the possible association between the characteristics of the activity/rest rhythm and obesity, as well as with various inflammatory biomarkers. 6) To examine if the circadian score developed in objective 1, is capable of capturing diseases such as obesity. This study was carried out on four hundred and thirty-two healthy children between 8 and 12 years, who were recruited in three schools from a Mediterranean area of Spain. Anthropometric and body composition measurements were determined. A 7-day food record and a sleep diary were performed for 7 days and the chronotype was determined using the Munich questionnaire (MCTQ). During the 7 days of study, children used a wristwatch placed on the non-dominant hand that integrated two different sensors, a temperature sensor to determine daily body temperature rhythms, and an actimeter, to determine of active/rest and body position rhythms. An integrating variable called TAP (Temperature, Activity and Position) was obtained. In a subsample of the population (n = 122), the daily rhythms of light exposure were analyzed through a pendant luxmeter. In addition, saliva samples were obtained for the determination of two circadian hormones such as cortisol (at 9:00 a.m., 2:00 p.m. and 11:00 p.m.) and melatonin (at 2:00 p.m. and 1:00 a.m.) and to analyze different inflammation biomarkers such as InterLeukins (IL 6 and 8), Tumor Necrosis Factor Alpha (TNFα), C-Reactive Protein (CRP), etc. Fasting serum samples were also drawn from a subsample of 79 children. On the other hand, the academic score of a subpopulation of children were collected (n = 92). The results obtained in this thesis show that we have been able to develop a novel circadian score using non-invasive circadian-tools, including the integrative variable TAP, which seems to be reliable in evaluating the circadian system in children. Children had better circadian function than adults. Also, girls appear to have better circadian function than boys. On the other hand, we confirm that several biomarkers in saliva are able to capture the life style and obesity degree of these children. Indeed, biomarkers such as CRP, TNFα and IL6 and 8 show changes related to BMI, food intake, and physical activity. These data indicate that the analysis of these pro-inflammatory biomarker in saliva may constitute a potential useful non-invasive and stress-free tool for future studies. Furthermore, we demonstrate the importance of the individual chronotype in school-age children and its relationship with chronodisruption and metabolic risk. Evening chronotype children, as objectively evaluated, presented more sleep disturbances, higher social jet lag, higher exposure to light at night, more obesity, higher metabolic risk and better academic scores in art than morning chronotypes. Moreover, this thesis provides a circadian and metabolic view of the detrimental association of habitual late eating in children. According to our results, those children who had a late dinner were more obese, had higher values of inflammatory biomarkers such as CRP and IL6, and had higher circadian alterations than children who had early dinner. Also, we demonstrate that alterations in the activity/rest rhythm are associated with BMI and proinflammatory markers in children, regardless of sleep duration and/or average daily physical activity. Finally, we have demonstrated that the circadian score is capable of detecting diseases such as obesity in school-age children. Good or poor circadian health will depend on factors such as sleep, timing food intake and physical activity, presence or absence of obesity, among others.