A three-year study of child brain development showed that children with high body mass index values tended to have worse episodic memory. Researchers reported a bidirectional association between these obesity indicators and performance in executive tasks. The study was published in JAMA Network Open.
Childhood obesity is a significant public health concern worldwide. Overweight children tend to remain overweight when they grow into adults. Additionally, the number of obese children has increased multifold in many developed countries in recent decades.
In adults, obesity is associated with worse cognitive functioning in several aspects. Studies have found obese children to have worse executive functioning, including verbal fluency, inhibitory control, and mental flexibility. There is mixed evidence for traits such as impulsivity, decision-making and sensitivity to reward. Additionally, obese children and adolescents tend to have worse attention, worse visuospatial performance, and lower motor skills. It, however, remains unknown whether obesity is a consequence of these specificities in psychological and brain functioning or their cause.
“The general concept regarding the relationship between brain and obesity is that obesity adversely affects brain health,” said study author Mohammad Nazmus Sakib, a postdoctoral research fellow at the University of Waterloo. “However, research in health neuroscience has proposed a bidirectional relationship, where the brain can also influence weight gain over time. This hypothesis has not been adequately examined using large-scale datasets, especially among adolescents who undergo significant brain maturation. This knowledge gap motivated us to investigate bidirectionality among the adolescent population.”
The researchers expected that cognitive functioning would be linked to later adiposity (adiposity means being overweight or obese) and that this link would be mediated by physical properties of the lateral prefrontal cortex region of the brain (i.e. its morphology). Their other assumption was that adiposity at the start of the study would be associated with cognitive functioning later in life and that this would be mediated by physiological parameters such as blood pressure.
They analyzed the results from the ABCD study, a longitudinal study of brain development in U.S. children. They used data from 11,878 children who were between 9 and 10 years of age at the start of the study. Data were collected at three time points – in 2015 and 1 and 2 years after that.
The researchers measured height and weight of participants, in order to calculate their body mass indexes, and their waist circumference. Participants completed a cognitive assessment battery (the National Institutes of Health Toolbox) that provided assessments of executive function, working memory, processing speed, attention, episodic memory, and language abilities. Participants underwent functional magnetic resonance imaging, from which the researchers obtained data on the form and shape of the lateral prefrontal cortex region of children’s brains.
Results showed that higher body mass index at the start of the study was associated with worse performance on the picture sequence task (that assesses episodic memory) at later time points. Children with greater waist circumference tended to also show worse performance on this task. On the other hand, better performance in picture sequence tasks and the assessment of executive function (the Flanker task) at the start of the study was associated with lower adiposity at later timepoints.
“This study highlights the significant role of brain health as a potential risk factor for weight gain,” Sakib told PsyPost. “Therefore, promoting and preserving brain health could be an effective strategy for maintaining a healthy weight.”
When associations with cognitive functions were analyzed individually, results showed that higher adiposity at the start of the study was linked to worse executive functioning at later timepoints. The reverse was also the case – worse executive functioning at the start of the study was linked to higher adiposity indicators (body mass index and waist circumference) at later points.
Statistical analysis showed that a model in which blood pressure mediates the link between early adiposity and later executive functioning is possible. Further analyses revealed links between adiposity and cognition to be mediated by thickness and volume of the middle frontal gyrus region of the brain. Physical activity was shown to be a plausible mediator of the link between certain aspects of early cognitive functioning and later adiposity.
“It is remarkable that weight status and brain health are interrelated and have an impact on each other from the early teenage years. Therefore, maintaining a healthy weight during childhood and adolescence is crucial for optimal brain development,” Sakib said.
The study sheds light on the link between obesity and cognition. However, it should be noted that it only used two measures of adiposity, thus limiting the ways in which the assumptions of bidirectionality of the adiposity-cognition link can be tested.
“To thoroughly investigate bidirectionality, additional follow-up data is needed as our analysis was limited by the amount of available data,” Sakib explained. “Additionally, future analyses should examine other cognitive domains, such as memory, to determine the extent of bidirectionality.”
“The present analysis is limited to U.S. adolescents, and therefore, future research should investigate bidirectionality in populations from other regions, particularly in developing countries.”
The study, “Bidirectional Associations Between Adiposity and Cognitive Function and Mediation by Brain Morphology in the ABCD Study”, was authored by Mohammad Nazmus Sakib, John R. Best, and Peter A. Hall.
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