Beyond insomnia, the conditions of obesity and depression are common underlying causes for excessive daytime sleepiness (EDS), according to a new study at Pennsylvania State College of Medicine. The findings could lead to more personalized sleep treatments for those with regular daytime drowsiness.
“In the medical field, there is a widespread belief that if you feel sleepy during the day, it’s because you didn’t get enough sleep,” said Julio Fernandez-Mendoza, assistant professor of psychiatry at the Sleep Research and Treatment Center at Pennsylvania State College of Medicine.
“We need to start abandoning this idea. If we continue to believe that the only cause of excessive daytime sleepiness is people sleeping too little, we are missing the vast majority of the population.”
“The main causes of a sleepy society are an obese society, a depressed society and, to some extent, people who have a physiological disorder. By looking at our patients more closely, we can start personalizing sleep medicine,” he added.
Up to 30 percent of the general population suffers from EDS, a condition characterized by drowsiness or sleepiness for most of the day that can include irresistible sleep attacks. Feeling overly tired during the day can reduce job productivity and increase errors and absenteeism and may lead to more serious issues such as car accidents.
Earlier studies have linked EDS with obesity, depression, and sleep apnea, but the new study is the first to use physiologic sleep data to identify causation and investigate the mechanisms behind it. It is also the first observational study of EDS over several years.
At the beginning of the study, researchers measured self-reporting of EDS and then again an average of 7.5 years later. Study participants (1,395 men and women) completed a comprehensive sleep history and physical examination and were evaluated for one night in a sleep laboratory.
The researchers also noted any sleep, physical and mental health problems and substance use and determined whether participants were being treated for physical and mental health conditions.
“Obesity and weight gain predicted who was going to have daytime sleepiness,” said Fernandez-Mendoza. “Moreover, weight loss predicted who was going to stop experiencing daytime sleepiness, reinforcing the causal relationship.”
The connection between body mass index and sleepiness was independent of how much sleep the participants got at night, meaning obese people may be tired during the day no matter how well they sleep.
Obesity is also linked to sleep apnea, a condition in which breathing pauses occur during sleep. A hallmark of sleep apnea is daytime sleepiness. Although it may seem logical to assume that sleep apnea causes fatigue in obese people, the study challenges this.
“Body weight predicted EDS better than sleep apnea,” Fernandez-Mendoza said.
“This data is also consistent with studies showing that CPAP (continuous positive airway pressure) machines greatly reduce the number of apneas, or pauses in breathing, that a person with sleep apnea experiences during the night, but don’t effectively reduce daytime sleepiness — probably because CPAP does not help reduce weight.”
The primary underlying mechanism that makes obese people feel overly tired is likely low-grade chronic inflammation. Fat cells, particularly from abdominal fat, produce immune compounds called cytokines that promote sleepiness, among other effects.
People with depression also had high incidence of EDS. Physiologic sleep disturbances, including taking longer to fall asleep and waking up in the middle of the night, explained their daytime drowsiness.
“People with depression typically ruminate, they have difficulty shutting their minds off and they are more likely to have elevated stress hormones,” Fernandez-Mendoza said.
“The mechanism that we believe is playing a role here is hyperarousal, which is simply going to bed and being too alert; in other words, people with depression feel fatigued but do not necessarily fall asleep during the day.”
The findings also showed that a minority of people with EDS have a physiologic sleepiness disorder of the central nervous system. They actually sleep longer than average at night, in part because they fall asleep faster than normal.
“Excessive daytime sleepiness has huge implications for public health and policy,” Fernandez-Mendoza said.
“Fatigue and sleepiness are the most common causes of poor work productivity and fatal car crashes. In our study we were able to causally link obesity and depression — disorders of epidemic proportions — with daytime sleepiness through different mechanisms; in fact, we found that individuals who lost weight did not complain of daytime sleepiness anymore.”
The findings indicate that a one-size-fits-all treatment for EDS — such as a prescription for sleeping pills and more sleep — will fail in the long term.
The study is published in the journal SLEEP.