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Higher adiposity in children causative factor in decreased activity levels
Increased adiposity in children appears to have a causal effect on decreased physical activity, suggesting that BMI may be a valuable target in initiatives to increase children’s activity levels, according to recent findings.
Notably, this causation may be bidirectional, with reduced activity levels in turn leading to increased adiposity, the researchers wrote.
In the Mendelian randomization analysis, researchers utilized data of 4,296 children aged 11 years and enrolled in the Avon Longitudinal Study of Parents and Children, a prospective birth cohort. Besides measuring the BMI of all participants, the researchers also gauged total body fat, expressed as fat mass index. This was obtained by imaging the participants with a DXA scanner, then dividing fat mass by height (in meters) squared. Children were also genotyped, and a weighted allelic score was established using 32 independent variables known to be strongly associated with BMI. In the Mendelian analysis portion of the study, this score was used as an instrumental variable for adiposity to approximate the causal effect of adiposity and physical exercise.
Age-adjusted linear regression was utilized to evaluate observational associations between adiposity and activity measures.
The observational analysis revealed that a 3.3 kg/m2 higher BMI was linked to 22.3 less movement counts/minute in total physical activity (95% CI, 17-27.6) and 2.6 minutes/day less moderate-to-vigorous intensity activity (95% CI, 2.1-3.1) and 3.5 minutes/day more sedentary time (95% CI, 1.5-5.5).
The Mendelian randomization analysis revealed that a 3.3 kg/m2 higher BMI was related to 32.4 less movement counts/minute in overall physical activity (95% CI, 0.9-63.9); 2.8 minutes/day less moderate-to-vigorous activity (95% CI, 0.1-5.5) and 13.2 minutes/day more stationary time (95% CI, 1.3- 25.2). Poor instrumentation of activity restricted investigation of the causality of physical activity on BMI.
“It is intuitive to think of and observe relationships between factors such as obesity and activity in the population,” the researchers said in a press release. “However, it is less clear in which direction these associations lie; whether they are causal, or whether it is worth allocating considerable resources to assessing the impact of potential interventions.”
Disclosure: One of the researchers is a member of the Editorial Board of PLOS Medicine.