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Fatness leads to inactivity, but inactivity does not lead to fatness: a longitudinal study in children (EarlyBird 45)
B S Metcalf1, J Hosking, A N Jeffery
1Department of Endocrinology and Metabolism, Peninsula Medical School, University Medicine, Level 7, Derriford Hospital, Plymouth PL6 8DH, UK. brad.metcalf@phnt.swest.nhs.uk
Insights
Fatness in children leads to inactivity, not the other way around. This finding suggests that promoting physical activity alone may not effectively combat childhood obesity due to this reverse causality.
Area of Science:
- Pediatric endocrinology
- Childhood obesity research
- Physical activity and health
Background:
- Childhood obesity is a significant public health concern.
- The causal relationship between body fatness and physical inactivity in children remains debated.
- Understanding causality is crucial for effective intervention strategies.
Purpose of the Study:
- To determine whether increased body fatness causes decreased physical activity or vice versa in children.
- To investigate the direction of causality between body fat percentage and physical activity levels in a pediatric cohort.
Main Methods:
- Prospective cohort study involving 202 children aged 7–10 years in Plymouth, England.
- Annual measurements of body fat percentage using dual-energy X-ray absorptiometry.
- Objective assessment of physical activity via Actigraph accelerometers over 7 consecutive days annually.
Main Results:
- Higher body fat percentage at age 7 predicted a decrease in moderate-to-vigorous physical activity over the next 3 years.
- Physical activity levels at age 7 did not predict subsequent changes in body fat percentage.
- A 10% higher body fat predicted a 4-minute daily decrease in moderate and vigorous activity intensity.
Conclusions:
- Findings suggest that fatness is a cause of physical inactivity in children, rather than the reverse.
- This reverse causality may explain the limited success of interventions solely focused on increasing physical activity for childhood obesity.
- Future obesity interventions may need to address fatness directly, alongside physical activity promotion.
Objective:
To establish in children whether inactivity is the cause of fatness or fatness the cause of inactivity.
Design:
A non-intervention prospective cohort study examining children annually from 7 to 10 years. Baseline versus change to follow-up associations were used to examine the direction of causality.
Setting:
Plymouth, England.
Participants:
202 children (53% boys, 25% overweight/obese) recruited from 40 Plymouth primary schools as part of the EarlyBird study.
Main Outcome Measures:
Physical activity (PA) was measured using Actigraph accelerometers. The children wore the accelerometers for 7 consecutive days at each annual time point. Two components of PA were analysed: the total volume of PA and the time spent at moderate and vigorous intensities. Body fat per cent (BF%) was measured annually by dual energy x ray absorptiometry.
Results:
BF% was predictive of changes in PA over the following 3 years, but PA levels were not predictive of subsequent changes in BF% over the same follow-up period. Accordingly, a 10% higher BF% at age 7 years predicted a relative decrease in daily moderate and vigorous intensities of 4 min from age 7 to 10 years (r=-0.17, p=0.02), yet more PA at 7 years did not predict a relative decrease in BF% between 7 and 10 years (r=-0.01, p=0.8).
Conclusions:
Physical inactivity appears to be the result of fatness rather than its cause. This reverse causality may explain why attempts to tackle childhood obesity by promoting PA have been largely unsuccessful.
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