Discussion
sleepiness
To the best of our knowledge, this is the first trial of its kind that investigates complete metabolic profiles combined with performance monitoring in humans over a multi-day period involving different sleep–wake schedules (control, sleep deprivation, and sleep restriction conditions in the same participants). Hereby, we aim to establish a candidate biomarker panel being indicative for sleepiness and its behavioral outcomes. For that purpose, established validated performance testsSince there are no easily detectable markers for different sleep phenotypes (i.e., chronotypes) yet, we expect that some metabolites will show good applicability in a certain (phenotype) group of subjects but not necessarily outside this given group. To exclude further confounding factors, only standardized, isocaloric meals and non-stimulating drinks will be offered and consumed at the same clock times. Furthermore, equal toothbrushes and additive-free toothpaste will guarantee unbiased oral hygiene comparability for salivary metabolomics analyses. Temperature and light emission will be controlled and match day and night conditions.To date, there are no robust and easily accessible biomarkers for the detection of sleepiness, even though the vast damage on society (health issues, accidents, etc.) is well known. Thus, our findings will be of high value for many related disciplines.