By contrast, too much light during the night can “disturb this carefully coordinated system,” Scheer says, pointing to research that shows how exposure to light during night hourscan cause blood sugar levels to increase. 

“In the modern world, we live in a weird lighting environment where we are typically indoors during the day,” a much dimmer environment compared to the outdoors, Scheer says. “During the night, we are introducing light where before there was none. We spend an enormous amount of time in front of screens—the TV, phones, computers—close to bedtime.” 

Researchers think that light at night could activate the sympathetic nervous system—involved in the “fight or flight” response—which is “mismatched with what we should do at night” and could cause dysregulation of glucose metabolism, Scheer says. 

Other biological pathways are also likely involved in how light affects metabolism, Dibben says. In laboratory experiments, for example, researchers have found that exposure to UVA, a type of ultraviolet light from the sun, triggers stores of nitrite in the skin to turn into nitric oxide. Nitric oxide widens blood vessels, which could potentially lower blood pressure and increase blood flow in ways that could improve glucose regulation, Dibben says.