What causes daytime drowsiness?

A new investigation illuminates the biological foundations of excessive daytime drowsiness, an ongoing and inappropriate desire to doze during the day — at work, during meals, or even mid-conversation — disrupting daily activities.

The research, published in The Lancet eMedicine, paves the way for examining how diet, lifestyle, and environmental factors interplay with genetic and biological mechanisms to influence alertness.

“Recent studies have pinpointed genetic variations linked to excessive daytime drowsiness, yet genetics only account for a fraction of the explanation,” stated co-corresponding author Tamar Sofer, director of Biostatistics and Bioinformatics at the Cardiovascular Institute at Beth Israel Deaconess Medical Center, as well as an associate professor at Harvard T.H. Chan School of Public Health and Harvard Medical School. “We aimed to discover biomarkers that could provide deeper insights into the mechanisms behind excessive daytime drowsiness and clarify why certain individuals experience persistent fatigue even when their sleep habits appear satisfactory.”

Researchers from Harvard-affiliated BIDMC and Brigham and Women’s Hospital utilized metabolite analysis to delve into the biology underlying excessive daytime drowsiness. Metabolites are small substances produced as the body performs its regular functions, ranging from hormone synthesis to nutrient metabolism and the elimination of environmental toxins. By quantifying these metabolites, researchers established a profile for excessive daytime drowsiness.

The team examined blood levels of 877 metabolites from samples collected from over 6,000 participants in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), a longstanding study funded by the National Institutes of Health since 2006. By cross-referencing this data with self-reported assessments of sleepiness on an official survey, the researchers identified seven metabolites significantly associated with increased levels of excessive daytime drowsiness.

The seven metabolites were found to be involved in the formation of steroids and other biological processes previously linked to excessive daytime drowsiness. When focusing solely on data from male participants, an additional three metabolites were uncovered, indicating potential gender-related biological variations in how excessive daytime drowsiness presents.

The results strengthen the proposition that excessive daytime drowsiness is not simply a consequence of insufficient sleep but may signify physiological conditions that could one day be diagnosed via blood tests or addressed through specific interventions.

“As we gain insight into the biological processes at play, we are starting to comprehend how and why EDS manifests, the early indicators that someone may have it, and the strategies we can employ to assist patients,” said lead author Tariq Faquih, a postdoctoral research fellow in Sofer’s lab, as well as the lab of Heming Wang at BWH, and a fellow in medicine at HMS. “These findings could eventually lead to novel methods for preventing or managing sleep disorders involving daytime drowsiness as a primary symptom.”

This research received partial support from the National Institutes of Health and the National Institute on Aging.