Life course exposures and later metabolic risk factors until young adulthood

Abstract

 Background Insights from a life course perspective potentially reduce the increasing trend of metabolic diseases. In particular, breastfeeding status and child growth are key modifiable exposures, as evidenced by the success of breastfeeding promotion interventions. Studies investigating the associations of breastfeeding status and child growth with later health were mainly conducted at young ages and findings remain controversial. This thesis investigated the associations of breastfeeding and child growth with metabolic risk factors into young adulthood and differences by sex. Methods This thesis took advantage of a large population-representative Chinese birth cohort, “Children of 1997”, from the non-Western developed setting of Hong Kong (n=8327). Breastfeeding status were classified as “exclusively breastfeeding for at least 3 months” (BF), “partially breastfeeding for any length of time or exclusively breastfeeding for less than 3 months” (MF) and “never breastfeeding” (FF). Weight and length/height measures were considered as weight-for-age z scores (WAZ), length/height-for-age z scores (LAZ) and body-mass-index-for-age z scores (BAZ), relative to the World Health Organization child growth standards/references. Overnight fasting blood samples at ~17.5 years were assayed to obtain fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), low- (LDL) and high- (HDL) density lipoprotein and triglycerides (TG). Blood pressure at ~17.5 years was converted to height-, age-, sex-specific systolic (SBPZ) and diastolic (DBPZ) blood pressure z scores, relative to the United States National High Blood Pressure Education Group reference 2004. Adjusted sex- and age-specific associations of breastfeeding status with infant growth from birth to 36 months were assessed using linear regression and mixed modelling, respectively. Adjusted sex-specific associations of breastfeeding status with overall BAZ up to 16 years were examined using generalized estimating equation. Adjusted associations of child growth at different phases from birth to puberty with metabolic risk factors were investigated using partial least squares regression. Results Breastfeeding status was differentially associated with infant WAZ gains by age, but not associated with overall BAZ up to 16 years in boys and girls. Initial size was unrelated to glycemic indicators and blood pressure, while lower LAZ at 3 months was associated with higher TG and lower HDL. Gains in WAZ from birth to 2 years and LAZ and BAZ from 3 months to 3 years were positively associated with SBPZ; higher LAZ gain from 3 months to 3 years was also associated with lower HDL and higher TG. Gains in WAZ from 2 to 8 years and BAZ from 3 to 8 years were adversely associated with blood pressure, glycemic indicators especially in FPG and lipid profile exclusively in TG among boys, and LAZ gain from 3 to 8 years was positively associated with FPG and SBPZ. Growth from 8 to 14 years was not associated with metabolic risk factors. Conclusion Breastfeeding status may affect short-term but not long-term growth. Greater growth especially in weight and body mass index during childhood may be more relevant to metabolic risk factors. Differential associations of child growth at various phases from birth to childhood with metabolic risk factors suggest the pathogenesis of metabolic diseases may differ.