It's about time: implications of chronoactivity on health and disease

Albalak, G. (2026)

Doctoral Thesis

Virtually all physiological processes in the human body follow circadian rhythms driven by the biological clock. When these rhythms are well aligned, they support health; when disrupted, they increase the risk of chronic disease. While the benefits of physical activity are well established, far less is known about whether when we move matters for (circadian) health.
This thesis introduces the concept of chronoactivity; the timing of physical activity in relation to the circadian system, and examines its relevance for cardiometabolic health, sleep, and mental health. Using large-scale observational data with objective accelerometry, alongside a randomized cross-over intervention study in older adults, this work investigates how morning, evening, and nighttime activity relate to common chronic conditions.
Across studies, morning physical activity was consistently associated with better metabolic outcomes, improved mood, and a lower risk of cardiovascular disease and depression, independent of total activity levels. The timing of activity also influenced sleep–wake rhythms, while nighttime activity was linked to adverse health outcomes.
Together, these findings highlight chronoactivity as a promising, low-cost, non-pharmacological strategy to enhance prevention and treatment.

• Chronobiology
• Zeitgeber
• Physical activity
• Public health
• Cardiometabolic disease
• Mental health
• Sleep

• All authors: Albalak, G.
• Supervisor: Bodegom, D. van
• Co-supervisor: Heemst, D. van; Noordam, R.
• Committee: Kiefte- de Jong, J.C.; Giltay, E.J.; Kervezee, L.; Beulens, J.W.J.; Lammers- van der Holst, A.M.
• Qualification: Doctor (dr.)
• Awarding Institution: Faculty of Medicine, Leiden University Medical Center (LUMC), Leiden University
• Date: 2026-05-06
• ISBN (print): 9789465373072
• Sponsorship: Leiden University Medical Center; The research described in this thesis was part of the Bioclock Consortium funded by a grant from the Dutch Research Council (NWO, Dutch National Research Agenda, Research along routes by consortia, 2021–2026, project number NWA.1292.19.077).