Exposure to natural light through a window appears to improve blood sugar control in people with type 2 diabetes, a small study suggests.
Our cells and tissues follow circadian rhythms, 24-hour cycles of metabolic activity that regulate functions such as blood sugar levels. Previous studies have shown that exposure to artificial light at night disrupts these rhythms, raising blood sugar levels, while spending more time outside in sunlight seems to enhance the body’s response to insulin, a hormone that helps keep these levels in check.
However, none of these studies explored the potential benefits of being exposed to natural light through a window, even though most people spend the vast majority of their time indoors.
To test this, researchers at Maastricht University in the Netherlands recruited 13 people with type 2 diabetes with an average age of 70, who spent 4.5 days in a room where they were solely exposed to natural light, through large windows, between 8am and 5pm.
The participants, who continued to take their usual diabetes medications, mainly sat at a desk where they had access to their phones and computers, with screens set to a low level of brightness. In the evenings, they were exposed to dim artificial light and had access to their devices until 11pm, before sleeping in complete darkness until 7am. They all ate three similar meals a day, designed not to make them gain or lose weight, and did the same exercises at fixed points across the 4.5 days.
Light-sensitive cells in the eye are central to regulating cycles of metabolic activity and are more sensitive to the shorter wavelengths found in natural light, which may explain why sunlight exposure has this effect.
Joris Hoeks at Maastricht University said further studies are needed to establish this, but for now, many people with type 2 diabetes could benefit from getting more natural light, even if that means just sitting by a window.
“It’s easy, accessible at no cost and available to everyone.” said Joris Hoeks.
It is unclear whether people with type 1 diabetes or prediabetes, when someone’s blood sugar is higher than usual but not high enough for a type 2 diabetes diagnosis, would benefit to the same extent.
Glen Jeffery at University College London said larger studies are needed to confirm the findings. Nevertheless, he added that “the importance of daylight is only slowly beginning to be appreciated.”