Interrelationship between Obesity and Sleep

Abstract

The purpose of this review was to evaluate the reciprocal relation and mutual impact between obesity and sleep. Nowadays it is well known that in 2013, the American Medical Association classified obesity as a disease and in 2014, more than 1.9 billion adults, 18 years and older, were overweight. Of these over 600 million were obese. The rapid rise in obesity prevalence in the modern world parallels a significant reduction in restorative sleep. Reduced sleep time and quality increases the risk for obesity. A majority of the theories linking human sleep disturbances and obesity rely on self-reported sleep. However, studies with objective measurements of sleep/wake parameters suggest a U-shaped relationship between sleep and obesity. Studies in animal models are needed to improve our understanding of the association between sleep disturbances and obesity. Genetic and experimenter-induced models mimicking characteristics of human obesity are now available and these animal models will be useful in understanding whether sleep disturbances determine propensity for obesity, or result from obesity. The study of the relationship between sleep and obesity dates back to the 1960s when investigators pointed out a link between body weight change and sleep disorders like narcolepsy and Pickwickian syndrome. Recent epidemiological and animal studies supported these earlier observations and showed a crucial interplay between sleep and body weight regulation. While it was recognized that 7–8 hours of uninterrupted sleep was optimal for adults, the reliance on self-reported sleep rather than objective measures has led to discrepancies in the literature focused on the relationship between sleep time and obesity, which has been extensively reviewed. Cross-sectional and cohort studies in children clearly indicated an association between short sleep and weight gain. Longitudinal studies in adults suggested greater weight gain or obesity with shorter nighttime sleep. In contrast, other studies showed an association between long-sleep duration, both at night and during the day, and greater body weight. When sleep/wake cycle was objectively measured, severe obesity was also associated with longer nighttime sleep in humans. Overall studies are consistent with a bimodal or U-shaped relationship between sleep time and body weight gain in adults. The presence of REM sleep during the active time period may impair energy metabolism and promote obesity in humans. Persons with narcolepsy/cataplexy, due to the loss of orexin-containing neurons or orexin receptors, had greater REM sleep propensity and more sleep onset REM periods during the active period and greater body mass index (BMI) than non-narcoleptics. In addition, studies demonstrated that elevated body weight was associated with decreased nocturnal total sleep and REM sleep in humans and suggested that endocrine changes such as reduced leptin and increased ghrelin mediated the association between sleep and obesity. These endocrine changes are suggested to be more sensitive to reduced REM sleep at night. In contrast, weight loss in humans significantly increased the percentage of nighttime REM and SWS sleep. Together these studies indicate that normal amounts of REM sleep at night may be crucial for normal body weight maintenance and that the occurrence of more REM sleep during the day may increase the risk for higher BMI in humans. Though the effect of the absolute amount of sleep on body weight change seems bimodal, other factors including sleep fragmentation and excessive daytime sleepiness EDS (components of sleep quality) appear to significantly impact body weight gain.