Published on 17th July 2019


Night-time exposure to blue light – i.e. the kind produced by the screens of commonly used devices – raises blood sugar levels and increases sugar intake in male rats, according to a recent study.[1]

To understand what happens with appetite and food choice after blue light exposure at night, rats were given the option to choose between nutritionally-balanced food (standard rodent food), water, lard, and sugar water. In order to model human light exposure, the rats used in the study were diurnal, i.e. awake during the day and asleep at night, rather than the typical nocturnal laboratory rats which are awake during night-time hours. 

It was found that after only one hour of nocturnal blue light exposure, male rats were found to have altered glucose tolerance, a warning sign of pre-diabetes. The male rats also drank more sugar when exposed to blue light than they did during the nights with no blue light exposure.

A statement from the Society for the Study of Ingestive Behavior, USA, said that the studies clearly showed that being exposed to light and especially to blue light at night is disruptive, and that – especially for males – screen use at night may increase the tendency to snack on sugary foods and disrupt the ability to process that sugar.  Although the rats were only tested after one night of light exposure, the authors believed that over time this could lead to weight-gain and the development of diabetes.

According to lead author Anayanci Masís-Vargas from the University of Strasbourg, the best way to protect ourselves from the harmful effects of blue light is to limit the amount of time we spend in front of screens at night. And if we do need to use these devices, she recommends using apps and night mode features that turn the screens more orange and less blue, or the use of blue light filtering goggles.


  1. Masís-Vargas A et al (2019). Acute exposure to blue light at night impairs glucose tolerance, alters insulin secretion and increase sugar intake in a diurnal rodent. Society for the Study of Ingestive Behavior.