A study just published in the Proceedings of the National Academy of Sciences shows that you can gain weight just by sleeping with a dim light on (like the glow from a nightlight).

In a very creative experiment, researchers discovered that mice exposed to dim light during their sleeping hours gained 50% more weight than mice sleeping in total darkness.

To confirm the effect of the light exposure in relation to other factors, the researchers reduced the caloric intake of the mice sleeping with the dim light on, and added more exercise to their routine.

Even with this intervention (less calories and more exercise) the mice still gained more weight than the mice sleeping in total darkness – amazing.

The authors of this study, from the Departments of Neuroscience and Psychology at Ohio State University and the Israeli Center for Interdisciplinary Research in Chronobiology at the University of Haifa, also found that the mice not sleeping in total darkness experienced glucose intolerance (a pre-diabetic condition).

It is too early to tell if this study will translate in the exact same way to humans.

However, common sleep advice suggests you stop using anything with an artificial glow – like watching television or playing on your laptop or cellphone – a couple hours before you go to bed.

Although this is surprising, we do know that hormones can be unpredictable! The night light could be disrupting melatonin or your circadian rhythms... no one knows for sure.

But starting tonight, I’m going to un-plug my daughter’s princess night light and my family and I are going to hit the hay in total darkness… at least until one of my kids gets spooked out!

Sources:

Nedeltcheva, Artlet V., et all. “Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity.” Annals of Internal Medicine. October 2010. Vol. 153, no. 7: 435-441.

Bedrosian, T.A., Fonken, L.K., Walton, J.C., Haim, A., & Nelson, R.J. (2011). Dim light at night provokes depression-like behaviors and reduces CA1 dendritic spine density in female hamsters. Psychoneuroendocrinology 36: 1062-1069.