December 10, 2019

expert reaction to study looking at BMI in 9-10 year olds and cerebral cortex thickness

Research, published in JAMA Pediatrics, reports that children aged between 9 and 10 who have higher BMI’s tend to have thinner cerebral cortex. 

Prof Alan Carson, Professor of Neuropsychiatry, University of Edinburgh, said: 

“This is an interesting study which addresses questions of the interface between brain, obesity and decision making. It strength is its size, the representative nature of the sample, and the brain imaging analysis. It is also noteworthy that they looked at behavioural correlates, in terms of intelligence tests, and correlated this to  brain structure. 

“However, it seemed to me that there were two main weaknesses. Firstly the executive, ie decision making, systems in the brain are only beginning to come ‘on line’ at the age that the children were studied. It is something of a moot point whether this follows chronological age, biological age (for instance influenced by puberty) or is independent. This may have a significant confounding effect on the results. Similarly one of the biggest confounders of obesity and of intelligence (at least as defined by cognitive tests) and to an extent puberty is socio-demographic status. This is highly likely to have an impact on the results but was not included in the model. This is slightly surprising as my understanding is that such data was collected in the overall cohort from which this study was derived. I think this means that the study needs to be interpreted with considerable caution. It is a useful study of its type but the results probably fit better in the highly nuanced, incremental  world of scientific knowledge and are less suited to mainstream reporting. In particular to simply say obesity has been found to be linked to smaller brain and less intelligence would be misleading and actively unhelpful to many kids who struggle with self esteem as it is.”

Dr Oyinlola Oyebode, Associate Professor in Public Health, Warwick Medical School, University of Warwick, said:

“This interesting and well conducted study raises many questions for future research. Because of the study design (data on BMI and on brain anatomy were collected at the same point in time) we don’t know the reasons for their findings. Perhaps the differences in brains cause the differences in BMI, for example because those with smaller prefrontal cortex make poor dietary decisions. This finding would suggest that those with less power to plan are more vulnerable to our current environment where often the unhealthy choices are the easiest ones to make. However, perhaps there are other explanations, for example perhaps the diet or potential lack of physical activity that affects the body, increasing body weight, also effects the brain. Also, using BMI, especially in children, and particularly on the cusp of puberty might also mean the result is due to bias. Further studies should examine whether the brain differences are also correlated with differences in body fat using other methods (such as waist circumference, scans or bio-electrical impedance) and could also look at which differences appear first in studies of children conducted over time.”

Dr Laura Dearden, Sir Henry Wellcome Post-doctoral Fellow, University of Cambridge, said:

“The press release is accurate in terms of reporting the key findings of the study. Although similar studies investigating a link between brain structure and body weight in adolescents have been conducted, this is a larger study. The findings that changes in the structure of this part of the brain are associated with increased BMI is consistent with previous studies in both animals and humans, as well as with studies showing a link between increased body weight and reduced measures of executive function such as working memory. Importantly, as this part of the brain is important for decision making, changes in the structure could explain why some children find it harder to eat less, and thus gain weight.

“The important issue missing from this study (as acknowledged by the authors) is which comes first: do changes in structure of the cortex cause increased weight gain, or does increased weight gain cause reduced thickness of the cortex. We know that nutrition and body weight during early life is critical for a child’s development- in particular the way the brain develops- and can potentially lead to weight gain later in life. Repeating this study at a younger age might help us understand whether these changes in the brain cause increased weight gain, or visa versa.

“The study shows that children with a higher BMI have changes in the structure of the brain and reduced memory performance, but it does not show conclusively that these changes in the brain cause the increased BMI. Therefore, I would say that wording such as high BMI is ‘linked/ associated’ with memory problems is appropriate.”

Prof Tara Spires-Jones, UK Dementia Research Institute Programme Lead, Deputy Director, Centre for Discovery Brain Sciences, The University of Edinburgh, said:  

“This is an interesting and well-conducted study by Laurent and colleagues from the University of Vermont looking at brain size, body mass index, and cognitive function in 9-10 year old children. They observed that in their group of over 3000 children, those with high body mass index (BMI) generally had a thinner cortex and lower scores on cognitive tests. 

“It is important not to jump to conclusions causally linking obesity to lower intelligence based on these data.  As the authors point out, this kind of experiment does not tell us whether the higher BMI caused the cortex of these children to be smaller, or whether having a smaller cortex for other reasons contributed to higher BMI perhaps through poor decision-making with regard to diet. It is also possible that the smaller cortex and higher BMI are not causally related. 

“This paper adds to a large amount of data suggesting that taking good care of your body is good for your brain, but more work needs to be done to fully understand the observed association between smaller cortex size and high BMI.”

Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“This paper is provocative as it seems to suggest being more overweight as a child means you will have lower memory abilities and some associated changes in brain.  However, this paper cannot be taken as saying excess weight causes these memory or brain differences. This is because many factors that lead children to be more overweight such as poorer diet, coming from less affluent backgrounds, and all the extra environmental and personal stresses that come with this could impact brain development and memory. In other words, many upstream factors could lead both to weight gain and memory/ brain issues rather there being a direct link between obesity and memory. Whatever the explanations, we need to work harder in all countries to help people more easily lead better lifestyles.”

Prof Jan Buitelaar, Professor of Neuropsychiatric and Development Disorders and Principal Investigator, Radboud Medical Centre, said:

“We cannot infer causality from these cross-sectional associations; for that, we need longitudinal data. It is unclear whether a prior thinner cortex and poor EF (executive functioning – for example working memory, planning) predisposes to obesity, or whether obesity (high BMI) leads to a thinner cortex and poor EF; or whether there are ‘third’ factors that drive the association (for example genetic factors).”

‘Associations Among Body Mass Index, Cortical Thickness, and Executive Function in Children’ by Laurent et al. was published in JAMA Pediatrics at 16:00 UK time on Monday 9^th December. 

DOI: 10.1001/jamapediatrics.2019.4708

Declared interests:

Prof Naveed Sattar: None

Professor Tara Spires-Jones: None

Prof Alan Carson: None

None others received.