Lack of sleep can be detected by saliva

Drowsiness while driving causes tens of thousands of accidents in the United States every year, and even more around the world. Some states have even passed laws to reduce the number of tired drivers on the roads. Scientists decided to investigate whether the metabolites in saliva change due to a lack of sleep. The goal was to develop a sleepiness test that could be performed anywhere, from the side of the road to a clinic.

“Until now, it has been impossible to biochemically measure sleep deprivation, even though it is one of the biggest problems of our time,” says Kremer, the author of the study. “Our study is the first to identify direct biomarkers of sleep deprivation in saliva under real-world conditions. This is an important step for forensic investigations.”

The study involved 20 healthy young men who typically slept for 7-9 hours per night. The participants underwent three sleep scenarios in a random order (with a week-long break between them):

• Sleep deprivation: one night without sleep.
• Sleep restriction: four nights with two hours of reduced sleep compared to their usual routine.
• Adequate rest: about eight hours of sleep.

Before and after each scenario, the scientists collected saliva samples and analyzed their metabolic composition. Using statistical methods, they identified 10 molecular differences between samples from sleep-deprived and well-rested participants. However, the limited sleep condition did not show significant metabolic differences from adequate rest.

The team then developed and trained a predictive model based on the identified metabolites in the saliva. The model correctly identified samples from sleep-deprived individuals in 94% of cases.

The model’s errors were generally associated with individual metabolic characteristics. For example, some participants did not return to a full-fledged metabolic profile even after eight hours of sleep, suggesting that this time was insufficient for complete recovery.

The results indicate that the set of metabolites in saliva forms a kind of sleepiness fingerprint. This opens up opportunities for practical applications, such as rapid driver drowsiness testing on the road.

Kremer’s team is currently preparing for a large-scale international validation of the model. The new study will analyze more than 1,000 saliva samples collected from shift workers, women, and frequent travelers.