The effect of early childhood growth trajectories on nutritional status and body composition at 2 years of age

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Background Paediatric obesity is rising globally, and the prevalence is rising faster in lowmiddle income countries (LMIC) than other regions. Early life growth patterns play critical role in shaping risks of chronic diseases later in life. However, the association between early childhood growth and adult disease risk may be mediated by body composition. However, there are few studies assessing the relationship between growth patterns and body composition during early childhood. The assessment of body composition early in infancy affords discernment into the fat mass and lean mass distribution; important factors for subsequent metabolic diseases. There is limited data on early childhood body composition in LMIC settings undergoing transition. Aims Therefore, the aims of this dissertation were to; (i) describe fat mass and fat-free soft tissue mass by air displacement plethysmography at birth, 1, 2, 3, 4 and 6 months, (ii) describe fat mass and fat-free soft tissue mass using deuterium dilution technique at 3, 6, 9, 12, 18 and 24 months; and to (iii) assess the association between childhood growth from birth to 24 months and fat mass and fat-free mass at 24 months in a cohort of South African urban infants. Methods The data for this dissertation was a secondary analysis of data drawn from the International Atomic Energy Agency Multicentre Body Composition Reference Study on singleton infants born in Soweto, South Africa between 2014 and 2019. The anthropometric measurements weight and length, skinfold thicknesses, and arm circumferences were collected at each visit. Fat mass (FM) (kg), fat free mass (FFM) (kg), Fat mass index (FMI), fat free mass index (FFMI), and percentage fat mass (%FM) were measured using Air displacement plethysmography (ADP) and isotope dilution method (Deuterium Oxide) from birth to 24 months. The birthweights were classified as: Small-for-gestational age (SGA) (below 10th percentile), appropriate-for-gestational age (AGA) (between 10th and 90th percentile) and iv large-for-gestational age (LGA) (above 90th percentile) using Intergrowth-21st growth standards. Age and sex adjusted height-for-age (HAZ), weight-for-age (WAZ) and weight-forheight (WHZ) z-scores were generated using the 2009 WHO child growth references (0 – 5 years) to assess nutritional status from birth to 2 years. The analyses of variance were used to assess differences in body composition between categories of birth weight. T-tests were used to assess differences in anthropometric measurements and body composition between sexes and levels of nutritional status. The multiple linear regression analyses were used to estimate the association between conditional growth 0-6months and 6-24months and body composition at 24 months. Results Boys had significantly higher weight at all ages, and were taller up to 15 months of age. Girls had higher FM at birth p<0.001) and 1 month (p<0.001) of age. There were no differences in FFM, FMI, and FFMI between sexes at all time points. SGA and AGA both had significantly higher %FM than LGA at 12 months. LGA had higher FM at 24 months. Children with stunting had significantly lower FM and FFM at 12 and 24 months. At 6 months, FFMI was significantly higher in children with stunting. Conditional relative weight 6-24 months had a stronger association with FM and FMI than conditional relative weight 0-6 months and birth weight. Conditional length in both 0-6 and 6-24 months was significantly associated with FM and FMI in females Conclusion The assessment of growth pattern and body composition early in infancy may prove valuable in understanding factors associated with prevalence of childhood obesity. Rapid weight gain beyond 6 months of age had a stronger associated with toddler body fat. SGA and LGA are disadvantaged extremes in infancy, likely to increase the risk for obesity.
A research report submitted in partial fulfilment of the requirement for the degree of Master of Science in Medicine to the Faculty of Health Sciences, University of the Witwatersrand, School of Clinical Medicine, Johannesburg, 2023
Paediatric obesity, Trajectories, Nutritional status, Early childhood