Associations between abdominal adiposity, body size and objectively measured physical activity in infants from Soweto, South Africa

Abstract

Objectives: Considering the importance of the early life period, in conjunction with the increasing prevalence of adiposity and insufficient physical activity already evident in early childhood, this study aimed to determine associations between abdominal adiposity, body size, and objectively measured physical activity in infancy. Methods: Infants (n=138, aged 3-24 months) from Soweto, South Africa were recruited to this cross-sectional study. Visceral (VAT) and subcutaneous abdominal fat (SAT) were measured using ultrasound. Physical activity was assessed using accelerometry and analysed at the hourly level. Multilevel linear regression analyses were run with body composition exposures adjusted for age, sex, and length; models with VAT and SAT were also adjusted for total abdominal fat. Results: Mean (SD) age was 11.8 (7.6) months; 86% were normal weight, 7% were underweight and 7% overweight. In linear models, no body composition variable was significantly associated with physical activity. Physical activity was higher with each increasing length tertile (ANOVA p<0.01); with a mean(95%CI) 29(60-60)mg in the lowest tertile, 39(71-71)mg in the middle tertile, and 50(81-82)mg in the highest tertile. Infants with normal weight had higher mean(95%CI) physical activity (40(70-80)mg) than underweight (34(73-85)mg, p=0.01) or overweight infants (31(63-78)mg, ANOVA p<0.01). When also adjusting for total abdominal fat, infants in the lowest SAT tertile had higher physical activity than those in the middle or highest SAT tertiles (p<0.01). Conclusions: These findings lend support for higher physical activity as a marker of healthy growth in the first two years of life. Significance While it is known that physical activity levels in infancy are often inadequate, and obesity is prevalent even in early childhood; there is limited and conflicting data on the relationship between physical activity and body composition in infancy. This is largely due to the nature of measures used. This study showed significant, non-linear relationships between infant objectively measured physical activity and adiposity assessed using abdominal ultrasound.