A small study suggests that sitting by a window to receive natural daylight can help manage blood sugar levels in people with type 2 diabetes. Researchers found that participants exposed to natural light spent more time within healthy glucose ranges compared to those under artificial lighting. The findings highlight the role of circadian rhythms in metabolic health.
Scientists at Maastricht University in the Netherlands conducted an experiment to examine how natural light affects blood sugar regulation in individuals with type 2 diabetes. Led by Joris Hoeks, the team recruited 13 participants with an average age of 70. Over 4.5 days, these individuals stayed in a room with large windows, allowing exposure to natural light from 8am to 5pm. They continued their regular diabetes medications and followed a structured routine: sitting at a desk with low-brightness screens on phones and computers, eating three standardized meals daily that maintained their weight, and performing identical exercises at set times. In the evenings, they experienced dim artificial light until 11pm and slept in total darkness until 7am.
For comparison, the same group participated in a similar setup a month earlier or later, but in windowless rooms illuminated only by artificial lights. Continuous glucose monitors tracked their levels, though technical issues limited usable data to 10 participants. Results showed that under natural light, blood sugar stayed in the healthy range of 4.4 to 7.2 millimoles per litre for 50% of the time, versus 43% during the artificial light phase. Hoeks noted that even these modest differences could reduce risks of complications like heart disease over time.
The benefits likely stem from light-sensitive cells in the eyes, which are more responsive to the shorter wavelengths in natural daylight and help synchronize 24-hour circadian rhythms governing metabolism and insulin response. Hoeks emphasized the simplicity of the approach: “It’s easy, accessible at no cost and available to everyone.” However, he cautioned that further research is required to confirm effects and determine applicability to type 1 diabetes or prediabetes.
Glen Jeffery of University College London agreed that larger trials are essential but pointed out that the value of daylight exposure is gaining recognition. The study appears in Cell Metabolism (DOI: 10.1016/j.cmet.2025.11.006).
