Earlier studies have shown that light sources such as televisions and smartphones can impact sleep patterns. Now, researchers have found evidence that bright light may also influence metabolism and insulin resistance.

Ivy Cheung, from the Northwestern University Feinberg School of Medicine, and colleagues recruited 19 healthy adults for a study that aims to determine why people who receive most of their bright light exposure in the morning were likely to weigh less compared with those who receive most of the bright light after 12 p.m.

Cheung and colleagues randomly assigned the participants to be exposed to bright light either 0.5 hour or 10.5 hours after waking, with participants in both groups eating while exposed to light.

The researchers then took subjective measures of sleep and hunger, as well as blood samples to measure glucose, cortisol, insulin, leptin and ghrelin, and compared these with the results when the participants were subjected to dim light.

The researchers found that participants who ate breakfast in the light tend to have higher insulin resistance and those who ate dinner in the light were likely to have higher peak glucose.

The findings showed that exposure to light, which was blue-enriched so it mimics natural light, in the morning and evening both led to higher insulin resistance.

The researchers also found that exposure to blue-enriched light in the evening results in higher peak glucose, which means a greater inability of insulin to compensate for glucose increase in the evening.

Insulin resistance is the inability of the body to move glucose off the bloodstream which can lead to buildup of blood sugar. Excess blood glucose may eventually result in weight gain and increased risk for diabetes.

"Our findings show that insulin was unable to acutely bring glucose levels back to a baseline level following a meal with bright light exposure in the evening," said Cheung.

"The results of this study emphasize that our lighting environment impacts our health outcomes."

The researchers likewise noted that as the study provides evidence that bright light exposure may affect metabolism, light can theoretically be used to manipulate metabolic function.

"Blue-enriched light exposure acutely alters glucose metabolism and sleepiness," the researchers wrote in their study, which was published in the journal PLOS ONE on May 18.

Finally, according to the researchers, "These results provide further support for a role of environmental light exposure in the regulation of metabolism."