Bert van der Horst is professor Chronobiology & Health at the Department of Molecular Genetics, Erasmus MC. By applying state of the art technology, he aims at obtaining fundamental knowledge on the biological/medical impact of the circadian system, which drives near (circa) 24 hour (diem) rhythms in behavior, physiology and metabolism. To keep phase with the day-night cycle, this circadian clock is daily reset by light. As such, excessive use of artificial light in modern society (referred to as light pollution) has a huge impact on our body clock. Added to this, our 24/7 economy requires many people to work at “non-standard” times. Epidemiological and experimental animal studies have associated chronic disturbance of our body clock (as encountered during shift work, jet lag and other abnormal light exposure conditions) with a variety of diseases, including cancer, metabolic syndrome and cardiovascular disease. Current research efforts focus on the development of biomarkers that allow an objective and quantitative assessment of the adverse effect of shift work and other conditions that disturb the circadian system. Such biomarkers are prerequisite to develop evidence-based measures that alleviate aberrant light and shift work-associated health risk and contribute to sustainable health and employability.