If you’re trying to lose weight, keeping the lights dim at night may help, a new study suggests.

There is increasing evidence that light and dark exposure patterns over time impact health outcomes such as body weight and food intake, so researchers at Northwestern University wanted to learn more.

Their previous research had found people who received the majority of their bright light in the morning weighed less than those who were exposed to most of their bright light after 12 p.m.  Although the reason for this isn’t fully understood, they decided to look at the effect of bright light on the body’s ability to metabolize glucose (blood sugar).  Mouse studies also have shown that mice kept in constant light have altered glucose metabolism and gain weight compared to control mice, they note.

Nineteen healthy adults were randomized to three hours of blue-enriched light exposure starting either one-half hour after waking (morning group) or 10 ½ hours after waking (evening group). Each person’s results were compared to their dim light exposure results as a baseline. The morning group ate breakfast in the light; the evening group ate dinner in the light.

The study found that blue-enriched light exposure acutely altered metabolic function in both the morning and the evening compared to dim light. While morning and evening blue-enriched light exposure both resulted in higher insulin resistance, evening blue-enriched light led to higher peak glucose. This suggests a greater inability of insulin to adequately compensate for the increase in glucose in the evening.

“These results provide further evidence that bright light exposure may influence metabolism,” says Dr. Kathryn Reid, the senior study author, of the research, which appears in PLOS ONE.