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

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.