The ExAMIN Youth SA study aims to generate new knowledge on the pathophysiology involved in early vascular aging among South African children and to identify early novel biological markers for predicting the subclinical development of hypertension and target organ damage related to cardiovascular disease. This study further implements state-of-the-art biochemical technology to measure a variety of biological markers including multiplex analyses and metabolomics. With the increasing prevalence of childhood hypertension and obesity, this study will be able to address especially behavioural contributors to hypertension development and to subsequently provide a backdrop for school-based primary prevention interventions.

Background: The current global widespread incidence of obesity and early cardiovascular deterioration are two of the most important future health care challenges. Physical inactivity and its associated unhealthy dietary intake among adolescents are of great concern, especially in a South African setting in which no current monitoring occurs to describe the impact of this sedentary and unhealthy lifestyle on cardiovascular health. With the estimated global prevalence of elevated blood pressure among children between 12-25%, there is a definite need to contribute to the lack of population level data in South Africa and how lifestyle behaviours impact on the burden of non-communicable disease.

Main aim: Our current study aims to build on previous findings to identify potential contributing factors that may adversely affect health outcomes in South African children. Additionally, we will cross-compare data with international centres on these health outcomes, and finally develop predictive models on target organ damage at 4-years follow-up from baseline data.

Design/Methods: We phenotyped a cohort of 1065 primary school children (all sexes, all ethnic groups and ages 5-9 years) according to their physical fitness and coordination, their dietary behaviours, psychosocial behaviour and current cardiovascular state. Parents of participating children provided information on socio-demographics including data on education, employment, types of dwelling, household amenities and parents' marital status, health habits, and lifestyle. The children will underwent the following measurements: anthropometric measurements of height, weight, waist circumference, triceps and subscapular skinfolds; stable isotope and bioelectric impedance analysis to measure body composition; blood pressure along with pulse wave analysis and aortic pulse wave velocity, static retinal vessel analysis (without mydriasis); accelerometry and a standardised physical activity questionnaire to measure physical activity. Physical fitness measures included motor skills, coordination, flexibility and cardio-respiratory fitness. Urinalysis will include creatinine, albumin, electrolytes, nitrates, nitrites, dimethylarginines, malondialdehyde, glucose, cardiovascular and kidney multiplex panels, and targeted metabolomics. Salivary analyses will include sex hormones and cortisol.

Outcomes: The primary outcomes for the baseline analysis include blood pressure, pulse wave velocity and retinal vascular calibres to address micro- and macrovascular compromise in relation to behavioural risk factors. In the follow-up phase of the study we will include carotid intima media thickness and left ventricular mass as outcomes of baseline predictors.

Timetable: The project was approved and is endorsed by the District Director of the Department of Education, and was approved by the Health Research Ethics Committee of the North-West University on 10 may 2017 (NWU-00091-16-A1). Data collection started in September 2017 and baseline measurements were concluded on 30 April 2019. Follow-up assessments will commence immediately in subsequent years for the 4-year follow-up phase of the study.

Inclusion Criteria:

• Children between ages 5 and 9 years (both sexes and all ethnicities).

Exclusion Criteria:

• Children who do not wish to participate or where the parents or caregivers did not provide permission.

The study population included 1103 children (at baseline) attending public primary schools in the Dr Kenneth Kaunda district, North West province, South Africa aged between 5 and 9 years of age. However, with a few missing (n=38) values of basic variables of interest such as sex, ethnicity or date of birth, we included a total 1065 children (mean age=7.44 years or 89.3 months). The majority of the participants were of African (n=579) and white (n=463) ethnicity, whereas only 2.2% (n=23) participants were of either Indian or mixed race. The sex distribution was similar in the white group, whereas the study unintentionally included more girls (58.5%) than boys (41.5%) in the black group.