TimeTeller for timing health: The potential of circadian medicine to improve performance, prevent disease and optimize treatment

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TL;DR

This narrative review presents the case for circadian medicine, arguing that the 24-hour biological clock regulates roughly 50% of human genes and that disruption of circadian rhythms is linked to diseases including cancer, diabetes, neurodegeneration, and sleep disorders. The authors describe TimeTeller, a non-invasive saliva-based in vitro diagnostic tool that profiles an individual's circadian rhythm by measuring core-clock gene expression (e.g., BMAL1, PER2) from eight daytime samples collected over 48 hours. The clinical significance lies in using personalized circadian profiles to optimize treatment timing (chronotherapy), reduce drug toxicity, improve efficacy, and guide lifestyle interventions such as sleep, meal timing, and exercise scheduling.

Full summary

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**Background:** The human circadian clock is an endogenous time-keeping mechanism that evolved to adapt organisms to environmental cycles such as day-night and feeding-fasting cycles. Approximately 50% of human genes exhibit 24-hour rhythmic expression in at least one tissue. Disruption of circadian rhythms is associated with sleep disorders, depression, diabetes, neurodegenerative diseases, obesity, and cancer. Despite the Nobel Prize awarded in 2017 for discoveries of the molecular mechanisms of the biological clock, clinical application of this knowledge remains scarce. The authors argue that the lack of non-invasive, user-friendly tools for characterizing the circadian clock in humans is a major barrier to implementing circadian medicine. This review provides an overview of circadian rhythm biology, existing assessment methods, and introduces TimeTeller, a novel in vitro diagnostic tool developed by the authors' group for circadian rhythm profiling.

**Methods:** This is a narrative review synthesizing published literature on circadian biology, chronotherapy, and existing tools for circadian assessment. The authors describe the molecular basis of the circadian clock, consisting of transcriptional-translational feedback loops of 14 core elements including positive regulators (CLOCK, BMAL1, ROR) and transcriptional repressors (PERs, CRYs, REV-ERB). The review surveys existing methods for circadian assessment including the BODYCLOCK Hairtest, Geneplanet saliva test, Cerascreen Melatonin Test, Salimetrics Salivary DLMO profile, wearable devices, and the Munich ChronoType Questionnaire (MCTQ). The authors then describe TimeTeller, their non-invasive saliva-based tool requiring eight samples collected over 48 hours during daytime only at four-hour intervals, with samples stable at room temperature for several days. Molecular characterization of core-clock gene expression (BMAL1, PER2) is analyzed using computational algorithms including harmonic regression and mathematical models based on ordinary differential equations to generate circadian parameters (amplitude, period, phase, mesor).

**Key Results:** The review reports that 56 of the top 100 best-selling FDA-approved drugs in the United States target genes expressed in a circadian manner, including all top 7 best-selling drugs. Additionally, 43% of all protein-coding genes show circadian rhythms, and nearly 50% of the top 100 drugs have a half-life of less than 6 hours, which the authors consider an important requirement for timed administration. A study screening over 1,000 FDA-approved drugs found that approximately 5% altered the circadian period. The overall drug development failure rate is 96%, with 90% or higher failing during clinical development; 40%–50% of compounds fail due to lack of clinical efficacy, while 30% show unmanageable toxicity. Multiple phase III clinical trials testing chronotherapy versus conventional treatment schedules showed improved anticancer treatment tolerability of up to fivefold and nearly double efficacy in experimental studies. A recent systematic review reported that 61% of analyzed studies described significant decrease in chemotherapy toxicity with chronotherapy. The authors cite their own published proof-of-principle study using a mathematical model of the circadian clock and drug pharmacology to optimize irinotecan administration timing in colorectal cancer to reduce toxicity.

**Clinical Implications:** The authors propose that circadian profiling using TimeTeller has applications in both healthy individuals and patients. For healthy individuals, personalized recommendations for sleep timing, physical exercise, meal timing, and light exposure can optimize performance and well-being. For patients, the tool may serve to monitor disease progression as a biomarker, optimize medical treatment timing according to drug targets, and detect circadian disruptions in conditions including Parkinson's disease, type 2 diabetes, cancer, and depression. Chronotherapy—administering treatments when cancer cells are most vulnerable and healthy cells are least vulnerable—aims to reduce side effects (nausea, vomiting, fatigue) and improve outcomes. Circadian rhythm sleep disorder is recognized under ICD-10-CM Code G47/G47.20. The authors envision that TimeTeller and similar tools will enable dynamic, adaptive treatment schedules, moving beyond generic 'x times daily' dosing toward personalized chronotherapy. They note that wearable devices can measure outputs of the circadian clock (temperature, heart rate, activity) but cannot measure the underlying circadian gene and protein expression network, positioning molecular profiling as a distinct and complementary approach.