Too much light exposure at night can cause depression, learning issues

14 Nov

It seems that “night lights” have been replaced in the digital age by laptops, televisions and phones, but a new study shows too much exposure to light after the sun goes down can have negative effects on the brain.

The study found that when people leave too many lights on at night, they are more at risk for depression and learning issues. These complications arise from more than bad sleep.

The study observed the effects of too much night light exposure on mice. Lead researcher and biology professor at John Hopkins University, Samar Hattar said that the finding is relatable to humans because we share special cells  (called intrinsically photosensitive retinal ganglion cells, or ipRGCs) in our eyes that affect the mood center in our brain the same way.

“Basically, what we found is that chronic exposure to bright light — even the kind of light you experience in your own living room at home or in the workplace at night if you are a shift worker — elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function,” Hattar said.

Hattar and research assistants exposed the mice to varying amounts of light and then monitored their behavior.

“Of course, you can’t ask mice how they feel, but we did see an increase in depression-like behaviors, including a lack of interest in sugar or pleasure seeking, and the study mice moved around far less during some of the tests we did,” he said. “They also clearly did not learn as quickly or remember tasks as well. They were not as interested in novel objects as were mice on a regular light-darkness cycle schedule.”

The main reason the mice showed symptoms of depression is because they showed increased levels of the stress hormone, cortisol. Cortisol is often the culprit in a diverse number of learning issues. To validate whether the mice were becoming inactive due to depression, Hattar treated the mice with Prozac, and observed their normal behaviors were restored.

In conclusion, Hattar warns that minimizing light exposure in the evening hours can curb this risk.

“I’m not saying we have to sit in complete darkness at night, but I do recommend that we should switch on fewer lamps, and stick to less-intense light bulbs: Basically, only use what you need to see. That won’t likely be enough to activate those ipRGCs that affect mood,” Hattar said.

One Response to “Too much light exposure at night can cause depression, learning issues”


  1. To study or to sleep? A college student’s dilemma | Layman's Terms Media - November 27, 2013

    […] Too much light exposure can cause depression, learning issues […]

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