Natural Light Exposure Improves Blood Glucose Control in Type 2 Diabetes: Study
A study published in Cell Metabolism has found that exposure to natural daylight through windows significantly improved glycemic control in people with type 2 diabetes. Participants staying in naturally lit rooms maintained healthy blood glucose levels 50% of the time, compared with 43% among those exposed only to artificial light. Researchers emphasized on natural light as a simple, cost-free, and widely accessible intervention to support metabolic health. The study was conducted by Jan-Frieder H. and fellow researchers.
Daylight is the key zeitgeber for the central biological clock in humans, but Hammond et al. reported that chronic daylight deprivation occurs in most work environments. The objective was to determine whether natural daylight, compared with artificial lighting, has an effect on glucose control, whole-body metabolism, circadian biology, or molecular signature in subjects with type 2 diabetes.
This is a crossover trial (NCT05263232) involving 13 adult type 2 diabetics. The subjects were subjected to natural light entering through windows or continuous artificial light for 4.5 consecutive days for each condition. Each participant acted as his/her own control. This enabled a comparison of the effects of the light environment on the subject.
The results from the CGM showed that exposure to natural daylight increased the time spent within the normal glucose range, as compared with exposure to artificial lighting. Substrate metabolism turned over towards higher fat oxidation rates during exposure to natural daylight. The results clearly show that exposure to natural daylight positively affects glucose regulation and energy metabolism in patients with type 2 diabetes.
Daylight exposure resulted in an increase in the evening melatonin rhythm, indicating better entrainment of the circadian rhythm. Analysis of skeletal muscle biopsies indicated that the primary myotubes demonstrated an entrained phase advance of the muscle molecular clock in response to the exposure to daylight. From the study, it can be observed that the primary myoblasts and primary myotubes respond to the exposure to daylight. In addition, it was found that the primary myoblasts showed
Multiparametric analyses indicated that daylight-induced changes existed for serum metabolites, lipid composition, and monocyte gene expression. It appears that the body undertakes systematic responses, particularly involving metabolism, immune function, and circadian rhythmicity, upon being exposed to daylight.
Exposure to natural daylight was linked to positive glucose homeostasis, increased fat oxidation, and favorable circadian rhythm and molecular mechanisms in type 2-diabetic patients. These outcomes strengthen the potential value of incorporating daylight exposure as a treatment for and prevention of metabolic disorders.
Reference:
Harmsen, J.-F., 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. (2025). Natural daylight during office hours improves glucose control and whole-body substrate metabolism. Cell Metabolism. https://doi.org/10.1016/j.cmet.2025.11.006
