Infant body mass index is unlikely to have much of an impact on a child’s mood or behavioral disorders

Infant body mass index is unlikely to have much of an impact on children’s mood or behavior disorders, according to a study 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 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 could contribute to mental health symptoms, or vice versa. Alternatively, a child’s environment could contribute to both obesity and mood and behavior disorders.

We need to better understand the relationship between childhood obesity and mental health. This requires separating the contributions of the child’s and parent’s genetics and environmental factors that affect the whole family.”

Amanda Hughes, lead author, Senior Research Associate in Epidemiology at Bristol Medical School, University of Bristol, UK

Hughes and his colleagues examined genetic and mental health data on 41,000 eight-year-old children and their parents from the Norwegian Mother-Father-Child Cohort Study and the Norwegian Medical Registry of Births. They assessed the relationship between the 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 took into account parental genetics and BMI.

The analysis found 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 ADHD or depressive 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 adolescents, it 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. The data suggested that having a mother with a higher BMI might be linked to depressive symptoms in children, but there was little evidence of any link between the child’s mental health and the father’s BMI.

“Overall, the influence of parental BMI on child mental health appears to be limited. As a result, interventions to reduce parental BMI are unlikely to have widespread benefits for children’s mental health,” he says. Alexandra Havdahl, a research professor at the Norwegian Institute of Public Health, Norway. Havdahl is co-senior author of the study along with 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 achieve large improvements in children’s mental health. On the other hand, policies that focus on social and environmental factors related to higher body weight , and that directly target children’s poor mental health, may be more beneficial,” concludes Hughes.