Gao, Mingyue; (2022) Age trajectories of cardiovascular risk factors in Chinese children and adolescents — secular trends, socioeconomic inequalities, and roles of growth and lifestyle factors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: High blood pressure (HBP) is the leading modifiable risk factor for cardiovascular disease (CVD) and accounted for 10.8 million global deaths by 2019. The heaviest HBP and CVD burden occurred in low- and middle-income countries (LMICs). The development of BP is important as it tracks from childhood into adulthood, and early-life BP has a profound influence on later-life CVD risks. But little is known about how child-to-adolescent BP trajectories have changed during recent decades, especially in LMICs. This PhD aimed to investigate trends in BP trajectories across recent cohorts among Chinese children and adolescents and explore the role of changing modifiable determinants. / Methods: This thesis used longitudinal data of 5,118 children and adolescents aged from 7 to 18 years in the China Health and Nutrition Survey (CHNS, 10 sweeps) during 1991-2015. Four birth cohorts (born in 1981-85, 1986-90, 1991-95, 1996-2000) were derived. Mixed-effects fractional polynomial models were applied to estimate the age-trajectories for BP and growth for each gender. First, I estimated mean BP trajectories across cohorts, with and without adjustment for BMI and height, to examine the impacts of changing physical growth on BP trends. Second, I investigated the association of socioeconomic position (SEP) with height and BMI and estimated the SEP disparities (high – low SEP) in mean growth trajectories across cohorts. Third, growth and BP trajectories across cohorts were further adjusted for SEP, lifestyle behaviours, and intergenerational influences to examine their impacts on trends in physical growth and BP. / Results: Child-to-adolescent BP trajectories shifted upwards across cohorts. Compared to the earliest cohort (1981-85), the mean increment of the latest cohort (1996-2000) was ~4mmHg during childhood and narrowed to 2~3mmHg (P<0.05) during late adolescence for both systolic and diastolic BP (SBP and DBP), except for little DBP increment for late-adolescent girls. Mean height and BMI trajectories also elevated during the same period. The height increment widened in childhood and narrowed post-puberty. The BMI increment persisted at 0.7~0.9kg/m2 for boys, while narrowed to 0.2kg/m2 in late adolescence in girls. The average height increment was 0.18 standard deviation for each successive cohort (SD/cohort), greater than the BMI increment of 0.09 SD/cohort. The increment in BP remained during childhood (P<0.05) but was largely explained by physical growth, with more explained by height than by BMI (Objective 1). High SEP was associated with higher mean height and BMI trajectories during childhood to adolescence. The large SEP disparities in height (e.g. equivalent to 3-5cm for 10-year-olds) persisted across cohorts. The SEP differences in BMI widened, from ≤0.5kg/m2 in the earliest (1981-85) to ~1kg/m2 in the latest cohort (1996-2000). Similar trends were found for SEP disparities in stunting and overweight/obesity. The findings were consistent for all SEP measures including community urbanization index, household income per capita, parental educational attainment and occupational social class (Objective 2). The proportion of first-born children, mean urbanization index and household income, the proportions of energy intake (%EI) from fat/protein and snacking behaviour, mean parental height, BMI and BP have all increased from the earliest (1981-85) to latest cohort (1996-2000). The increasing physical growth was mainly explained by trends in SEP and parental body size, which accounted for 45-58% in height and 54-72% in BMI trends. Parental body size contributed partly as the shared lifestyle components. The increasing BP trajectories were mainly explained by increasing body size and parental BP, which accounted for 71-78% in SBP and 57-62% in DBP trends. The impacts of changing SEP and lifestyle on BP trends were mainly through the increasing physical growth across cohorts (Objective 3). / Conclusion: In China, the upward shift of child-to-adolescent BP trajectories during the past decades was mainly explained by increasing physical growth, with a greater role of height than BMI. Short stature was associated with low-SEP backgrounds and greater BMI with high-SEP. SEP disparities in height persisted over time, whereas in BMI widened across cohorts. The increasing trends in SEP measures and parental body size explained most of the rising childhood growth. In addition, the rising childhood growth and parental BP largely explained the elevation in BP trajectories among Chinese youth. The main findings in China were consistent with other LMICs. Family-based interventions considering the household SEP backgrounds and parental history of obesity or HBP should be taken to prevent childhood obesity and HBP, especially in fast-developing countries.

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