Obesity and depression, and not just lack of sleep, may be responsible for regular drowsiness, a new study has found.
Researchers from Pennsylvania State University said the findings could lead to more personalised sleep medicine for those with excessive daytime sleepiness (EDS).
As much as 30 per cent of the general population experiences EDS - daytime drowsiness or sleepiness occurring throughout the day that can include irresistible sleep attacks, researchers said.
The new study measured self-reporting of EDS at baseline and again an average of 7.5 years later in 1,395 men and women.
Study participants completed a comprehensive sleep history and physical examination and were evaluated for one night in a sleep laboratory.
The researchers also recorded 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 Julio Fernandez-Mendoza, assistant professor of psychiatry at the Sleep Research and Treatment Center at Penn State College of Medicine.
"Moreover, weight loss predicted who was going to stop experiencing daytime sleepiness, reinforcing the causal relationship," said Fernandez-Mendoza.
The association between body mass index and sleepiness was independent of sleep duration, meaning obese people may be tired during the day no matter how much they sleep at night.
Depressed individuals in the study 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," Fernandez-Mendoza said.
