Summary: Despite common belief, new research shows that a child’s body weight has little effect on mood or behavior disorders.
Source: University of Bristol
According to research led by the University of Bristol and published today, childhood body weight measurement is unlikely to have a major impact on children’s mood. eLife.
The results suggest that some previous studies that have shown strong links between childhood obesity and mental health may not fully account 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, children’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 Dr Amanda Hughes, lead author of the Population Health Sciences (PHS) study at Bristol Medical School.
“This requires teasing out the genetic contributions of children and parents and the environmental factors that affect the entire family.”
Dr Hughes and colleagues examined genetic and mental health data from the Norwegian Mother, Father and Child Cohort Study and Medical Birth Registry of 41,000 eight-year-old children and their parents.
They evaluated the relationship between children’s body mass index (BMI)—the ratio of weight to height—and symptoms of depression, anxiety, and ADHD. Parental BMI and parental BMI are used to distinguish the effects of genetics on the children from the effects of other factors on the whole family.
The analysis found a small effect of the child’s own BMI on anxiety symptoms. Furthermore, there was conflicting evidence as to whether a child’s BMI influenced depressive or ADHD symptoms. This suggests that policies aimed at reducing childhood obesity are unlikely to have a significant impact on the prevalence of these conditions.
“At least for this age group, the effect of a child’s own BMI seems to be small. For older children and adolescents, it may be more important,” said Neil Davies, professor at University College London (UCL).
When looking at the effect of parental BMI on children’s mental health, the team found little evidence that parental BMI influenced children’s ADHD or anxiety symptoms. The data suggested that having a mother with a high BMI may be associated with more depressive symptoms in children, but there was no evidence of any relationship between child mental health and father BMI.
“Overall, the effect of parental BMI on child mental health appears to be limited. “For this reason, interventions to reduce parental BMI are unlikely to have a broad impact on children’s mental health,” adds Alexandra Havdahl, Research Professor at the Norwegian Institute of Public Health.
“Our results suggest that interventions designed to reduce childhood obesity are unlikely to produce significant improvements in children’s mental health. On the other hand, policies that target the social and environmental factors associated with high body weight and directly target poor child mental health may be more beneficial,” Hughes concluded.
So Neurodevelopment, Weight and Behavior Research News
Preliminary study: Open Access.
“Body mass index and childhood symptoms of depression, anxiety, and attention-deficit hyperactivity disorder: a Mendelian randomization study in families.” by Amanda M. Hughes et al eLife
Body mass index and childhood symptoms of depression, anxiety, and attention-deficit hyperactivity disorder: a Mendelian randomization study in families.
A higher BMI in childhood is associated with emotional and behavioral problems, but these associations may not be causal. The results of previous genetic studies indicate causal effects but may also reflect the influence of demographics and family environment.
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 examined the effect of BMI on depression, anxiety, and attention deficit hyperactivity disorder (ADHD) symptoms at age 8 years. We applied Mendelian randomization in our family, which accounts for familial effects by controlling for parental genotype.
Using Mendelian randomization estimates of genetic variation associated with BMI in adults, a child’s own BMI increases anxiety symptoms (per 5 kg2 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 affect the child’s depression symptoms (at 5 kg/m).2 increase in maternal BMI, beta = 0.11 SD, CI: 0.02,0.09, p=0.01). However, Mendelian randomization within families using retrospective genetic variants associated with childhood body size did not support an effect of BMI on these outcomes. There was little evidence of either parental BMI influencing the child’s ADHD symptoms or whether the child’s or parents’ BMI influenced the child’s anxiety symptoms.
We found consistent evidence that child BMI influences anxiety symptoms and ADHD symptoms. The effect of parental BMI was limited data. Genetic studies of unrelated samples of individuals or using genetic variants associated with adult BMI may have overestimated the causal effects of child BMI.
This research was done by the Health Foundation. It is part of the HARVEST collaboration, which is 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, HealthVest, Novo Nordisk Foundation, University of Bergen, Regional Health Authority of South-East Norway, Trond Møn Foundation, Regional Health of Western Norway Authority, Norwegian Diabetes Association, UK Medical Research Council. The Medical Research Council (MRC) and the University of Bristol support the MRC Integrated Epidemiology Unit.