Study finds 'likely biological and genetic overlap' between carpal tunnel syndrome and migraine

Child’s body weight has limited effects on mood and behavioral problems, study finds

According to a study published today in eLife [20 December].

The findings suggest that some previous studies, which have shown a strong link between childhood obesity and mental health, may not have fully considered 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 problems is unclear. Obesity can contribute to mental health symptoms, or vice versa. Alternatively, a child’s environment can contribute to both obesity and mood and behavior disorders.

“We need to better understand the relationship between childhood obesity and mental health,” says lead author Amanda Hughes, senior research associate in epidemiology at Bristol Medical School, University of Bristol, UK. “This requires disentangling the contributions of children’s and parents’ genetics from environmental factors affecting the whole family.”

Hughes and his colleagues looked at the genetic and mental health data of 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 the children’s body mass index (BMI) – a relationship between weight and 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 took into account parental genetics and BMI.

The analysis revealed a minimal effect of a child’s own 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. “At least for this age group, the impact of a child’s own BMI seems small. For older children and teenagers this might be more important,” says Neil Davies, a professor at University College London, UK.

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. Data suggested that having a mother with a higher BMI may be linked to depressive symptoms in children, but there was little evidence of a link between child mental health and BMI from father.

“Overall, the influence of a parent’s BMI on a child’s mental health appears limited. Therefore, interventions aimed at reducing parental BMI are unlikely to have generalized beneficial effects on children’s mental health,” says Alexandra Havdahl, research professor at the Norwegian Institute of Public Health, Norway. Havdahl is co-lead author of the study alongside Neil Davies and Laura Howe, professor of epidemiology and medical statistics at Bristol Medical School.

“Our results suggest that interventions designed to reduce childhood obesity are unlikely to provide large improvements in children’s mental health. On the other hand, policies that target social and environmental factors related to body weights higher, and that directly target poor mental health in children, may be more beneficial,” concludes Hughes.


“Body mass index and childhood symptoms of depression, anxiety, and attention deficit hyperactivity disorder: an intrafamilial Mendelian randomization study” by Amanda Hughes et al. in eLife [open access]


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