Sleep extension improves neurocognitive functions in chronically sleep-deprived obese individuals

Abstract

Background: Sleep deprivation and obesity, are associated with neurocognitive impairments. Effects of sleep deprivation and obesity on cognition are unknown, and the cognitive long-term effects of improvement of sleep have not been prospectively assessed in short sleeping, obese individuals.

Objective: To characterize neurocognitive functions and assess its reversibility.

Design: Prospective cohort study.

Setting: Tertiary Referral Research Clinical Center.

Patients: A cohort of 121 short-sleeping (<6.5 h/night) obese (BMI 30-55 kg/m(2)) men and pre-menopausal women.

Intervention: Sleep extension (468±88 days) with life-style modifications.

Measurements: Neurocognitive functions, sleep quality and sleep duration.

Results: At baseline, 44% of the individuals had an impaired global deficit score (t-score 0-39). Impaired global deficit score was associated with worse subjective sleep quality (p = 0.02), and lower urinary dopamine levels (p = 0.001). Memory was impaired in 33%; attention in 35%; motor skills in 42%; and executive function in 51% of individuals. At the final evaluation (N = 74), subjective sleep quality improved by 24% (p<0.001), self-reported sleep duration increased by 11% by questionnaires (p<0.001) and by 4% by diaries (p = 0.04), and daytime sleepiness tended to improve (p = 0.10). Global cognitive function and attention improved by 7% and 10%, respectively (both p = 0.001), and memory and executive functions tended to improve (p = 0.07 and p = 0.06). Serum cortisol increased by 17% (p = 0.02). In a multivariate mixed model, subjective sleep quality and sleep efficiency, urinary free cortisol and dopamine and plasma total ghrelin accounted for 1/5 of the variability in global cognitive function.

Limitations: Drop-out rate.

Conclusions: Chronically sleep-deprived obese individuals exhibit substantial neurocognitive deficits that are partially reversible upon improvement of sleep in a non-pharmacological way. These findings have clinical implications for large segments of the US population.

Trail registration: www.ClinicalTrials.gov NCT00261898. NIDDK protocol 06-DK-0036.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Neurocognitive function at baseline.

Left Figure: Results of deficit scores and individual neurocognitive tests. Right Figure: Results of the IGT per subsequent block of the test. The left vertical axis depicts the percentage of individuals in the following categories of neuropsychological function levels: impaired (t-score 0–39), below average (t-score 40–44), average (t-score 45–54), and above average (t-score 55–100). The right y-axis shows the mean±SD of the t-scores for each separate test. Mean and SD for deficit scores are not shown, because these variables exhibited a skewed distribution. Memory was tested by Rey-DR, the CVLT-II SD and the CVLT-II LD. Attention was tested by the CVLT-II Sum and by the TMT-A. Motor skills were assessed by the GPeg Dom and the GPeg Non-Dom. Executive functions were tested by the WCST, the TMT-B and the IGT. For all t-score computations, age was taken into account. In addition, ayears of education were taken into consideration for the t-scores for the WCST and IGT, and bgender was taken into account for the CVLT scores. cEducation, race, and gender were all taken into account for t-scores of the TMT, GPeg, and FAS. Abbreviations: GDS  =  Global Deficit Score, DDS  =  Domain Deficit Score, Rey-DR  =  Rey Complex Figure Test Delayed Recall, CVLT-II SD  =  California Verbal Learning Test II Short Delay, CVLT-II LD  =  California Verbal Learning Test II Long Delay, CVLT-II Sum  =  California Verbal Learning Test II Sum Score, TMT-A =  Trail Making Test Part A, TMT-B =  Trail Making Test Part B, GPeg Dom  =  Grooved Peg Board Test Dominant Hand, GPeg Non-Dom  =  Grooved Peg Board Test Non-Dominant Hand, WCST  =  Wisconsin Card Sort Test, IGT  =  Iowa Gambling Task.