Although CPAP is shown effective at reducing OSA and EDS, a significant proportion of people with moderate to severe OSA continue to experience excessive sleepiness, even after adequate treatment (Panossian, L. Veasey, S). Some of this sleepiness may be the consequence of irreversible injury to wake neurons from OSA, but more recently obesity and diet have been shown to be significant factors that influence sleepiness in both OSA and obese patients.
Obesity is the largest risk factor for OSA (Panossian, Veasey). In severely obese individuals, defined by a body mass index >35 kg/m, the prevalence of excessive daytime sleepiness and OSA is over 30% (Panossian, Veasey). Vgontzas et al. compared sleepiness in obese individuals with and without OSA, finding similar prevalence’s of sleepiness in individuals. In another study, obese patients underwent bariatric surgery and showed significant improvement in OSA and daytime sleepiness as measured by the Epworth Sleep Scale (Panossian, Veasey).
Short nocturnal sleep times are a common cause of daytime sleepiness and are considered a risk factor for obesity. Short nocturnal sleep times were shown to alter metabolics, favoring weight gain, increased appetite, and insulin resistance. One physiological response to obesity that could disrupt nocturnal sleep is heightened sympathetic activity. Obese individuals (especially those with increased abdominal visceral fat) are more likely to have greater noradrenalin spillover into systemic circulation, elevated urinary noradrenalin levels, and increased efferent muscle sympathetic nerve activity (disrupting nocturnal sleep).
Sleep, food intake, and diet are important factors to consider in daytime sleepiness. Regular ingestion of foods with high fat content and that are loaded with excess nutrients can predict excessive daytime sleepiness and poor quality of nocturnal sleep. For years people attributed the sleepiness after a very large Thanksgiving meal to tryptophan in the turkey typically served at this meal. As it turns out, the amount of tryptophan needed to induce sleep is orders of magnitude larger than the amount ingested in even a very large Thanksgiving dinner. However, a high-glycemic meal acutely increases tryptophan availability (Panossian, Veasey).
Recent studies have identified profound effects of either sleep restriction on feeding, or of food restriction on sleep. Less sleep has been shown to affect leptin and ghrelin levels, which can alter (increase/decrease) appetite (Panossian, Veasey). In two studies where leptin levels were measured at multiple time points throughout the day and food intake was controlled, several days of sleep deprivation or restriction to 4 hours/night in young healthy men resulted in increased appetite and decreased leptin levels (Mullington JM, Chan JL, Van Dongen HP).
While sleep restriction influences feeding and weight, food deprivation (eating very little) can modulate wakefulness in people. In humans, arousal from sleep is an important protective response to potentially life-threatening hypoglycemia, particularly in individuals with insulin-dependent diabetes mellitus (Gais S, Borne J, Peters A).
Obesity, diet, food intake, and lifestyle choices effect wakefulness, sleep cycles and are major contributors to EDS apart from other known causes like OSA. Much research is still yet to be done to determine the relationship that OSA, obesity, and other lifestyle factors have on EDS individually as well as their effect on one another collectively. Nonetheless, we must ensure that we manage obesity through our diet and the types of foods we eat, as well as make healthy lifestyle decisions to optimize sleep and counteract EDS and other sleep related disorders like OSA.
Gais S, Born J, Peters A, et al. Hypoglycemia counterregulation during sleep. Sleep 2003;26(1):55-9
Mullington JM, Chan JL, Van Dongen HP, et al. Sleep loss reduces diurnal rhythm amplitude of leptin in healthy men. Journal of neuroendocrinology 2003;15(9):851-4.
Panossian, L. Veasey, S. Daytime Sleepiness in Obesity: Mechanisms Beyond Obstructive Sleep Apnea. Journal of Sleep. Accepted for publishing (Journal issue not selected yet).
Spiegel K, Tasali E, Penev P, Van Cauter E. Brief communication: Sleep curtailment in
708 healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med 2004; 141(11): 846-50.