Associations of early life growth with health at age 22 years as measured by an allostatic load index: birth to twenty plus cohort
Growth in early life is associated with various individual health outcomes in adulthood, but limited research has been done on associations with a more comprehensive measure of health. Combining information from multiple biological systems, the allostatic load score provides such a quantitative measure of overall physiological health. Using longitudinal data from the Birth to Twenty Plus cohort in South Africa, an allostatic load score in young adulthood (at age 22 y) was calculated and associations with birth weight and linear growth and weight gain from age 0-2 y and 2-5 y were examined, as mediated by trajectories of body mass index and pubertal development in later childhood and adolescence. Missing measures of components of the allostatic load measure were addressed using multiple imputation by chained equations. Association with total allostatic load score were assessed using Poisson regression, while associations with high allostatic load was assessed using logistic regression. Differences in total allostatic load score between males and females were small, though levels of individual biological factors contributing to allostatic load differed by sex. Increased weight gain from age 2 to 5 y among males was associated with an increased risk of high allostatic load, but no other early life measures were associated with allostatic load. Increased adiposity through childhood and adolescence in females was associated with higher allostatic load in early adulthood. These results illustrate that patterns of early life growth are not consistently associated with a higher allostatic load. While more research is needed to link allostatic load in young adulthood to later health outcomes in settings like South Africa, these results suggest that increased adiposity during childhood and adolescence represents a critical factor and potential early sign of later physiological health risk.
A Dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science. Johannesburg, 2019