Netherlands: Spending office hours in natural daylight rather than under artificial lighting may improve glucose regulation and metabolic health in people with type 2 diabetes (T2D), a study published in Cell Metabolism by Jan-Frieder Harmsen from Maastricht University Medical Center in the Netherlands and colleagues has revealed.
Circadian rhythm disruption has been increasingly linked to metabolic disorders, including T2D. The day–night light cycle is a key synchronizer of the body’s internal clock, and reduced
daylight exposure—common in modern indoor work environments—may contribute to impaired metabolic regulation. While prior studies have focused on the adverse effects of nighttime light exposure, the metabolic impact of natural daylight during working hours has remained unclear.
To explore this, the researchers conducted a randomized crossover study involving 13 adults with T2D. Participants spent 4.5 consecutive workdays (8:00 AM to 5:00 PM) in either an office with ample natural daylight through large windows or a windowless office with constant artificial lighting. After a four-week washout period, they crossed over to the alternate lighting condition. The study included eight women and five men, with a mean age of 70 years, a mean fasting plasma glucose of 8.1 mmol/L, and an average HbA1c of 6.8%.
The key findings were as follows:
Continuous glucose monitoring showed no significant difference in average glucose levels between natural daylight and artificial lighting conditions.
Participants spent significantly more time within the normal glucose range when exposed to natural daylight compared with artificial light.
A similar trend favoring natural daylight was observed using the American Diabetes Association–defined time-in-range, although this did not reach statistical significance.
Natural daylight exposure was associated with beneficial changes in whole-body substrate metabolism.
Indirect calorimetry showed reduced carbohydrate oxidation and increased fat oxidation during waking hours under daylight conditions.
Plasma free fatty acid levels were higher following a mixed-meal challenge when participants worked in natural light, supporting greater fat utilization.
Evening melatonin levels increased with natural daylight exposure.
Multi-omic analyses revealed daylight-related changes in circulating metabolites, lipids, and immune-related transcripts.
Skeletal muscle cells showed shifts in internal circadian timing after daylight exposure, indicating an effect on peripheral biological clocks.
Overall, the study suggests that natural daylight during office hours supports better glucose control and promotes a healthier metabolic profile in individuals with T2D. The authors emphasize that since most people spend the majority of their time indoors, limited access to daylight may be an overlooked environmental factor contributing to metabolic disease. Improving natural light exposure in workplaces could represent a simple, non-pharmacological approach to support metabolic health, meriting further investigation.
Reference:
Harmsen, J., Habets, I., Biancolin, A. D., Lesniewska, A., Phillips, N. E., Metz, L., Sanchez-Avila, J., Kotte, M., Timmermans, M., Hashim, D., De Kam, S. S., Schaart, G., Jörgensen, J. A., Gemmink, A., Moonen-Kornips, E., Doligkeit, D., Van de Weijer, T., Buitinga, M., Haans, F., . . . Hoeks, J. (2026). Natural daylight during office hours improves glucose control and whole-body substrate metabolism. Cell Metabolism, 38(1), 65-81.e10. https://doi.org/10.1016/j.cmet.2025.11.006
