Blue light at night linked to mood disorders

Most of us are guilty of checking our emails or social media updates before bedtime, but new research could prompt changes in our pre-sleep rituals. Ohio State University and Salk Institute researchers have found that - in Siberian hamsters, at least - blue light has the worst effect on mood, followed closely by white light.

However, hamsters exposed to red light at night showed significantly less evidence of depressive symptoms and brain changes - and those kept in total darkness at night fared better still.

The research examined the role of ipRGCs - specialised photosensitive cells in the retina that detect light and send messages to the part of the brain that regulates the body’s circadian clock. Some research suggests that these cells also send messages to parts of the brain that play a role in mood and emotion.

“Light at night may result in parts of the brain regulating mood-receiving signals during times of the day when they shouldn’t,” said study co-author Tracy Bedrosian, a postdoctoral researcher at the Salk Institute. “This may be why light at night seems to be linked to depression in some people.”

“These cells are most sensitive to blue wavelengths and least sensitive to red wavelengths,” said co-author Randy Nelson, Professor of Neuroscience and Psychology at the Ohio State University. “We wanted to see how exposure to these different colour wavelengths affected the hamsters.”

After exposing the hamsters to four weeks of night-time conditions with no light, dim red light, dim white light (similar to that from light bulbs) or dim blue light, the researchers ran tests for depressive-like symptoms and also examined the hamsters’ hippocampus.

Hamsters exposed to white or blue light displayed evidence of mood problems and had significantly reduced density of dendritic spines compared to those who lived in total darkness or were exposed only to red light. A lowered density of dendritic spines has been linked to depression.

“The behaviour tests and changes in brain structure in hamsters both suggest that the colour of lights may play a key role in mood,” Nelson said. “In nearly every measure we had, hamsters exposed to blue light were the worst off, followed by those exposed to white light.

“While total darkness was best, red light was not nearly as bad as the other wavelengths we studied.”

Nelson and Bedrosian said they believe these results may be applicable to humans. We may all benefit from limiting light at night from computers, televisions and other electronic devices, they said. And, if light is needed, the colour may matter.

“If you need a night light in the bathroom or bedroom, it may be better to have one that gives off red light rather than white light,” Bedrosian said.

The study appears in the 7 August 2013 issue of The Journal of Neuroscience.

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