Natural daylight during office hours improves glucose control and whole-body substrate metabolism

Chronic lack of daylight is increasingly considered as a risk factor for metabolic diseases, such as type 2 diabetes (T2D). In a randomized cross-over design (NCT05263232), 13 individuals with T2D were exposed to natural daylight facilitated through windows vs. constant artificial lighting during office hours for 4.5 consecutive days. Continuous glucose monitoring revealed that participants spent more time in the normal glucose range and whole-body substrate metabolism shifted towards a greater reliance on fat oxidation upon daylight. In vitro assessment of the muscle clock displayed a phase advance after daylight exposure. Multi-omic analyses revealed daylight-induced differences in serum metabolites, lipids and monocyte transcripts. Our findings suggest that natural daylight exposure during office hours has a positive metabolic impact in individuals with T2D and could potentially support the treatment of metabolic diseases.