Background: The preventable risk factors for cardiovascular diseases (CVD) and diabetes cluster together and can be tracked from childhood into adulthood. There is evidence that sleep, cardiorespiratory fitness and socioeconomic status (SES) are related to the component risk factors of cardiometabolic syndrome, but this is mainly in adults. Current interventions to prevent cardiometabolic syndrome, also, are not robust enough and multisectoral approaches are still lacking in preventing these preventable risk factors. The aim of this thesis is to evaluate prevalence, identify some of the causes of these risk factors, their social determinants and how they are associated with another in English schoolchildren. Setting: Field·based research including schoolchildren from the East of England, United Kingdom. Methods: Cross~section of English state schoolchildren between lO~16 years participating in the East of England Healthy Hearts study. Height, weight and blood pressure (BP) measured by stadiometer, weighing scales and automated BP monitors using standard procedures respectively. Cardiorespiratory fitness assessed by the 20m shuttle~run test. Demographic data, screen time, sleep & wake time and physical activity (P A) levels were measured using questionnaires. Schoolchildren level of deprivation was measured using English Index of Multiple Deprivation. Metabolic risk profiles were categorised based on weight status and SBP status. Findings: Overall, 36% of schoolchildren were exposed to over 2 hours of daily screen time. Those reportiIlg <2h daily screen time were more likely to be active than 1 • . those reporting 2-4 h (OR 1.51, 95%CI 1.26-1.82) or >4h (OR 2.26, 95%CI 1.91 - 2.67). Prevalence of elevated mean arterial pressure (MPJl) was 14.8% overall but rose to 35.7% in those who were both obese and unfit. When compared with schoolchildren engaging in PA daily with adults in their household, schoolchildren who have reported no PA daily with adults in their household were likely (OR 1.54, 95%CI 1.07-2.20) to have an elevated MR profile. Rural children were more active than those from urban areas, but this was not evident when a trilateral division was used. About 40% of schoolchildren go to bed late at night. Late bedtime was associated with deprivation in schoolchildren. Compared to those with <2hours of daily screen time, the odds ratios for late bedtimes were higher in schoolchildren who spend 2-4 hours on screen time (OR 1.50, 95%CI 1.07- 2.09) and highest in those with> 4 hours of daily screen time (OR 1.97, 95%CI 1.34-2.89). Interpretations: Sedentary behaviour, parental influences, cardiorespiratory fitness, place and location of habitation are associated with the causes of CVD and component factors of cardiometabolic syndrome in schoolchildren. There was a high prevalence of>2h daily screen time in English schoolchildren. PA is lower in children reporting 2-4h versus <2h daily screen time and lower still in those classified'as heavy users (>4h) independent of deprivation, Increasing cardiorespiratory fitness level may have a positive impact on the weight-related elevations of MAP seen in obese and overweight schoolchildren. Joint PA with an adult within household could increase schoolchildren's cardiorespiratory fitness level, PA level and may reduce the risk of metabolic diseases. Rural environments support PA in children but not PA of adole scents, Town and fringe areas with mixed elements of rural and urban land use appear to fac ilitate and sustain PA in both children and adolescents, High screen time 2 , j and deprivation may explain lateness in bedtime in English schoolchildren. Family centred interventions may be important to reduce screen time and improve metabolic profile .