Does lack of sleep affect overweight teenagers more?

In a recent study published in JAMA Neurology, researchers examined how adolescent sleep duration influences the link between cognitive function and obesity. The results showed that overweight or obese adolescents experienced greater cognitive impairment after sleep reduction compared to normal-weight adolescents.

Obesity is quickly becoming a serious problem among children in the United States. Neurobiological evidence and cognitive test results link obesity to cognitive difficulties. The multifactorial nature of this association makes it difficult to identify the causal mechanisms of cognitive impairment. Neuroanatomical damage can lead to increased food intake and obesity. Biological factors such as insulin resistance and low-grade inflammation can also cause cognitive impairment.

Poor sleep quality is strongly associated with increased fat mass, increased appetite due to high levels of cortisol and ghrelin and low leptin levels, as well as poor food choices. Sleep disturbances also affect cognitive function, but it is unclear exactly how reduced sleep affects the relationship between fat mass and cognitive function.

In this study, researchers hypothesized that reduced sleep impairs various aspects of cognitive function, and that these negative effects would be more pronounced in adolescents with high levels of body fat compared to adolescents with normal weight.

Unlike previous studies that used only body mass index (BMI) to assess obesity, this study also used body fat percentage (TBF%). Adolescents aged 14 to 19 years were included in the study if they were healthy and did not have sleep disorders, eating disorders, intellectual disabilities or eating difficulties.

The study included three laboratory visits for adolescents and their parents. At the first visit, parents completed dietary and demographic questionnaires. Baseline participant measurements included bioelectrical impedance analysis, performance of cognitive tests, and assessment of weight and height. The subsequent two visits included two random orders of two actigraphy-verified sleep conditions: sleep restriction to 4 hours and adequate sleep to 9 hours.

The results showed that the negative effects of sleep reduction on cognitive function were greater in adolescents who were obese or overweight. They performed worse in global cognitive function, cognitive flexibility, fluid cognition, and attention after one night of insufficient sleep.

The use of TBF% has highlighted the limitations of using BMI to assess obesity. Higher TBF% was found to be associated with lower cognitive flexibility, fluid cognition, and processing speed after one night of insufficient sleep. TBF% thresholds were significantly higher for all three cognitive domains compared with previously used values for children, indicating that the risk of cognitive impairment increases significantly only in adolescents with obesity or severe obesity.

With adequate sleep, there were no differences in cognitive function between overweight and normal-weight adolescents. Similarly, in normal-weight adolescents, reducing sleep did not have a significant effect on cognitive function.

The study found that insufficient sleep had a more negative impact on cognitive functions, including fluid cognition, cognitive flexibility, attention, and processing speed, in adolescents who were obese or overweight compared to adolescents of normal weight.