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

Abstract: Contrary to popular belief, a new study finds that a child’s weight has little effect on mood or behavior 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 conducted by the University of Bristol and published today in eLife.

The results suggest that some previous studies, which have shown a strong link between childhood obesity and mental health, may not have fully taken into account family genetics and environmental factors.

Children with obesity 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 also contribute to obesity and mood and behavioral disorders.

“We need to better understand the relationship 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 teasing out the contributions of child and parent genetics and environmental factors that affect the whole family.”

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

They assessed the relationship between children’s body mass index (BMI)—the ratio of weight to height—and symptoms of depression, anxiety, and ADHD. To help separate the effects of the children’s genetics from the effects of other factors affecting the entire family, they also took into account the parents’ genetics and BMI.

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

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

When they looked at the effect of parental BMI on children’s mental health, the team found little evidence that parental BMI affected children’s ADHD or anxiety symptoms. The data suggested that a mother with a higher BMI might be associated with depressive symptoms in the children, but there was little evidence of any relationship between the child’s mental health and the father’s BMI.

“Overall, the influence of parents’ BMI on children’s 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 Havdahl, research professor at the Norwegian Institute of Public Health.

“Our results suggest that interventions designed to reduce childhood obesity are unlikely to significantly improve children’s mental health. On the other hand, policies that target the social and environmental factors associated with overweight, and that directly target poor mental health in children, may be more beneficial,” Hughes concluded.

About this news about neurodevelopment, weight and behavior research

Author: Press office
Source: University of Bristol
Contact: Press Office – University of Bristol
Picture: The image is in the public domain

Original research: Open access.
“Body mass index and symptoms of depression, anxiety and hyperactivity disorder in childhood: a Mendelian randomization study within families” by Amanda M Hughes et al. eLife

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Abstract

Body mass index and symptoms of depression, anxiety and hyperactivity disorder in childhood: a Mendelian randomization study within families

Background:

Higher childhood BMI is associated with emotional and behavioral problems, but these associations are not necessarily causal. The results of 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 Norwegian Medical Birth Register (MBRN). We investigated the influence of BMI on symptoms of depression, anxiety and attention deficit hyperactivity disorder (ADHD) at the age of 8 years. We applied within-family Mendelian randomization, which takes into account familial effects by controlling for parental genotype.

The results:

Within-family Mendelian randomization estimates using genetic variants associated with adult BMI suggested that child BMI increased 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 the mother’s BMI or related factors may independently influence the child’s 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 either assessment that parent BMI influenced child ADHD symptoms or that child or parent BMI influenced child anxiety symptoms.

Findings:

We found inconsistent evidence that a child’s BMI affected their depression and ADHD symptoms, and little evidence that a child’s BMI affected their anxiety symptoms. There was limited evidence of an influence of parental BMI. Genetic studies in samples of unrelated individuals, or using 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. Funding of individual co-authors: European Research Council, Regional Health Authority of South-East Norway, Norwegian Research Council, Helse Vest, Novo Nordisk Foundation, University of Bergen, Regional Health Authority of South-East Norway, Trond Mohn Foundation, Regional Health Authority of Western Norway, Norwegian Diabetes Association, UK Medical Research Council. The Medical Research Council (MRC) and the University of Bristol are supported by the MRC Integrative Epidemiology Unit.