In a recent study published in the journal JAMA Neurology, researchers evaluated how adolescent sleep duration impacts the association between cognitive function and adiposity. The results suggested that overweight or obese adolescents might experience a greater degree of adverse cognitive effects after sleep restriction than adolescents within the healthy weight range.

Study: Effect of Sleep Restriction on Adolescent Cognition by Adiposity. Image Credit: Prostock-studio / Shutterstock

Background

Obesity is rapidly becoming a serious health concern among the pediatric population in the United States. Studies based on neurobiological data and cognitive performance assessments suggest that obesity is also associated with cognitive difficulties.

However, the multifaceted and complex nature of the association between obesity and cognitive function makes it difficult to decipher the causal mechanisms of the cognitive difficulties. Neuroanatomical impairments could lead to increased food consumption, leading to obesity. Obesity-associated biological factors such as insulin resistance and low-grade inflammation could lead to cognitive impairments. Research suggests that metabolic dysfunction, inflammation, or inadequate physical activity could independently impact cognitive function.

Poor sleep quality has strong associations with increased adiposity, greater appetite due to high cortisol and ghrelin and low leptin levels, as well as poor choices about nutritional foods. Impaired sleep has also been found to influence cognitive function. However, whether and how sleep restriction moderates the link between adiposity and cognitive function remains unclear.

About the study

In the present study, the researchers hypothesized that restricted sleep would impair various aspects of cognitive function and that the negative effects of sleep restriction on cognitive function would be higher in adolescents with higher adiposity than in adolescents within the healthy weight range.

Previous similar studies have used only body mass index (BMI) as a measure of adiposity, which is erroneous since BMI cannot distinguish between muscle mass and adiposity. To circumvent these shortcomings, the current study used total body fat percentage or TBF% as an additional measure of adiposity.

Adolescents between the ages of 14 and 19 were included in the study if they were healthy and did not have any sleep disorders, eating disorders, intellectual disability, learning disorders, or difficulty eating or feeding. The exclusion criteria also consisted of using any medications that could impact appetite or sleep, BMI in the fifth percentile, and a high score on the food fussiness scale.

This randomized crossover study consisted of three lab visits for the adolescents and their parents or caregivers. The first visit consisted of the parents’ completing questionnaires on childhood eating behavior, as well as food and demographics. Baseline measurements of the adolescent participants taken during the first visit included bioelectrical impedance analysis, completing a cognitive battery, and assessments of weight and height.

The subsequent two visits consisted of a randomized order of two sleep conditions confirmed through actigraphy. The duration of the sleep condition was one night, which followed a washout period of two nights of adequate sleep. The two sleep conditions consisted of one restricted sleep condition of only 4 hours of sleep and one adequate sleep condition of 9 hours of sleep. Actigraphy was used to confirm the participant’s adherence to each sleep condition, after which a cognitive battery was administered.

Results

The results indicated that the adverse effects of restricted sleep on cognitive function were more significant among obese or overweight adolescents as compared to adolescents in the normal weight range. Obese or overweight adolescents performed poorly in areas of global cognition, cognitive flexibility, fluid cognition, and attention after one night of inadequate sleep as compared to adolescents who were not overweight.

The use of TBF% in this study also highlighted one of the drawbacks of using BMI as a measure of adiposity and one of the downsides of the low TBF% pediatric cut-offs used to define overweight or obesity. The study found that higher TBF% was associated with lower performance in cognitive flexibility, fluid cognition, and processing speed after one night of inadequate sleep.

However, the results also showed that the cut-offs for TBF% were significantly higher for all three cognitive areas than for the pediatric cut-offs used thus far. These findings indicated that the risk of cognitive impairments from sleep restriction was significantly elevated only for adolescents who were obese or severely obese and did not apply to all obese or overweight adolescents in a similar manner.

In cases of adequate sleep, no difference in cognitive function was noted between adolescents who were overweight or those within the healthy body weight range. Similarly, for adolescents who were not overweight or obese, the sleep restriction did not significantly change the various areas of cognition that were tested.

Conclusions

Overall, the study found that inadequate sleep had a greater negative impact on various aspects of cognitive function, including fluid cognition, cognitive flexibility, attention, and processing speeds, among adolescents who were obese or overweight than among those who did not have unhealthy body weight.