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A child’s body weight has a limited effect on mood and behavioral disorders

A child’s body weight has a limited effect on mood and behavioral disorders

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Summary: Contrary to popular belief, a new study reveals that a child’s body weight has little effect on mood or behavioral disorders.

source: University of Bristol

Childhood body mass index is unlikely to have a major impact on children’s mood or behavioral disorders, according to research led by the University of Bristol and published today in eLife.

The results suggest that some previous studies that have shown a strong link between childhood obesity and mental health may not have fully accounted for family genetics and environmental factors.

Obese children are more likely to be diagnosed with depression, anxiety, or attention deficit hyperactivity disorder (ADHD). But the nature of the relationship between obesity and these mental health conditions is unclear.

Obesity can contribute to mental health symptoms or vice versa. Alternatively, a child’s environment may contribute to both obesity and mood and behavioral disorders.

“We need to better understand the link between childhood obesity and mental health,” said lead author Dr Amanda Hughes, senior research fellow in epidemiology at Bristol Medical School: Population Health Sciences (PHS) at the University of Bristol.

“This requires disentangling the contributions of child and parental genetics and environmental factors affecting the whole family.”

Dr Hughes and colleagues examined genetic and mental health data on 41,000 eight-year-old children and their parents from the Norwegian Mother, Father and Child Cohort Study and the Norwegian Medical Birth Registry.

They assessed the relationship between children’s body mass index (BMI) – a ratio of weight to height – and symptoms of depression, anxiety and ADHD. To help separate the effects of children’s genetics from the influence of other factors that affect the whole family, they also take into account parental genetics and BMI.

The analysis found a minimal effect of a child’s BMI on their anxiety symptoms. There was also conflicting evidence about whether a child’s BMI influenced their depressive or ADHD symptoms. This suggests that policies aimed at reducing childhood obesity are unlikely to have a large impact on the prevalence of these conditions.

The results suggest that some previous studies that have shown a strong link between childhood obesity and mental health may not have fully accounted for family genetics and environmental factors. Image is in the public domain

“At least for this age group, the impact of a child’s BMI appears small. For older children and adolescents it may be more important,” said Neil Davies, professor at University College London (UCL).

When they looked at the effect of parents’ BMI on children’s mental health, the team found little evidence that parents’ BMI affected children’s ADHD or anxiety symptoms. Evidence suggests that having a mother with a higher BMI may be associated with depressive symptoms in children, but there is little evidence of an association between child mental health and father’s BMI.

“Overall, the impact of parental BMI on child mental health appears to be limited. As a result, interventions to reduce parents’ BMI are unlikely to have widespread benefits for children’s mental health,” added Alexandra Havdal, research professor at the Norwegian Institute of Public Health.

“Our results show that interventions designed to reduce childhood obesity are unlikely to lead to large improvements in child mental health. On the other hand, policies that target social and environmental factors associated with higher body weight and that directly target poor mental health in children may be more beneficial,” Hughes concluded.

About this news about neurodevelopmental, weight and behavioral research

Author: Press office
source: University of Bristol
Contact: Press Office – University of Bristol
Image: Image is in the public domain

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Original Research: Free access.
Body mass index and childhood symptoms of depression, anxiety, and attention deficit hyperactivity disorder: A within-family Mendelian randomization study” by Amanda M Hughes et al. eLife


Summary

Body mass index and childhood symptoms of depression, anxiety, and attention deficit hyperactivity disorder: A within-family Mendelian randomization study

Background:

Higher childhood BMI is associated with emotional and behavioral problems, but these associations may not be causal. Results from previous genetic studies suggest causal effects, but may reflect the influence of demographics and family environment.

Methods:

This study used data on 40,949 8-year-old children and their parents from the Norwegian Mother, Father and Child Cohort Study (MoBa) and the Medical Birth Register of Norway (MBRN). We examined the influence of BMI on symptoms of depression, anxiety, and attention deficit hyperactivity disorder (ADHD) at 8 years of age. We applied within-family Mendelian randomization, which accounts for family effects by controlling for parental genotype.

Results:

Within-family randomized Mendelian estimates using genetic variants associated with adult BMI suggested that a child’s own BMI increased their depressive symptoms (at 5 kg/m2 increase in BMI, beta = 0.26 SD, CI = −0.01,0.52, p=0.06) and ADHD symptoms (beta = 0.38 SD, CI = 0.09,0.63, p=0.009). These estimates also suggest that maternal BMI or related factors may independently influence child depressive symptoms (at 5 kg/m2 increase in maternal BMI, beta = 0.11 SD, CI:0.02,0.09, p=0.01). However, within-family Mendelian randomization using genetic variants associated with retrospectively reported childhood body size did not support an influence of BMI on these outcomes. There was little evidence from any assessment that parental BMI influenced child ADHD symptoms or that child or parental BMI influenced child anxiety symptoms.

Conclusions:

We found conflicting evidence that child BMI influenced depression and ADHD symptoms and little evidence that child BMI influenced anxiety symptoms. There is limited evidence on the influence of parental BMI. Genetic studies in samples of unrelated individuals or the use of genetic variants associated with adult BMI may have overestimated the causal effects of the child’s own BMI.

Financing:

This research was funded by the Health Foundation. It is part of the HARVEST collaboration supported by the Research Council of Norway. Individual co-author funding: European Research Council, Regional Health Authority of South-East Norway, Research Council of Norway, Helse Vest, Novo Nordisk Foundation, University of Bergen, Regional Health Authority of South-East Norway, Trond Foundation Mohn, Regional Health Authority of Western Norway, Norwegian Diabetes Association, UK Medical Research Council. The Medical Research Council (MRC) and the University of Bristol support the MRC Unit for Integrative Epidemiology.


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