Associations of body composition at birth and accretion from 0 to 5 years with kidney function and volume at the 10-year follow-up: the Ethiopian Infant Anthropometry and Body Composition birth cohort

Background: Fat mass (FM) and fat-free mass (FFM) in early life are associated with later obesity and cardiometabolic disease. Objectives: This study aimed to assess the associations of FM and FFM at birth and conditional FM and FFM accretion from 0 to 5 y with kidney outcomes at the 10-y follow-up. Methods: The Ethiopian Infant Anthropometry and Body Composition birth cohort included term infants born in Jimma town, with a birth weight >= 1500 g, and having no congenital malformations. Air-displacement plethysmography was used to measure body composition. Serum cystatin C was determined and kidney dimensions were assessed by ultrasound when children were aged similar to 10 y. Conditional growth modeling was used to compute FM and FFM accretion between different time points over 0-5 y. Multiple linear regression analysis was used to examine associations of birth FM and FFM and conditional FM and FFM accretion in selected age periods with serum cystatin C and total kidney volume at the 10-y follow-up. Results: A total of 350 children were followed up at a mean age of 9.8 (+/- 1.0) y. A 1 standard deviation (SD) higher conditional FFM accretion from 3 to 6 mo was associated with 7.6% [95% confidence interval (CI): 1.9%, 13.0%) lower serum cystatin C but higher conditional FFM accretion 48-60 mo was associated with 5.3% (95% CI: 1.9%, 9.0%) higher serum cystatin C. A 1 SD higher conditional FM accretion in the periods 6-48 mo and 48-60 mo was associated with beta = 7.7 (95% CI: 4.8, 10.7) and beta = 6.4 (95% CI: 1.6, 11.1) cm(3) greater kidney volume, respectively. A 1 SD higher birth FFM and FFM accretion in the periods 3-6 mo, 6-48 mo, and 48-60 mo was associated with beta = 4.7 (95% CI: 2.1, 7.2), 14.1 (95% CI: 6.3, 22.0), 4.2 (95% CI: 0.9, 7.4), and 7.1 (95% CI: 2.5, 11.7) cm(3) greater kidney volume, respectively. Conclusions: A higher conditional FFM gain in age from 3 to 6 mo results in better kidney function at the 10-y follow-up, whereas a higher conditional FFM gain in age from 4 to 5 y results in a lower kidney function. Kidney volume at the 10-y follow-up is associated with higher birth FFM and higher conditional FM or FFM growth in most growth periods.