August 20, 2013
From VOA Learning English, this is the Health Report.
Some colors that people see late at night could cause signs of the condition mental health experts call clinical depression. That was the finding of a study that builds on earlier study findings. They showed that individuals who live or work in low levels of light overnight can develop clinical depression.
Doctors use the words clinical depression to describe severe form of depression. Signs may include loss of interest or pleasure in most activities, low energy levels and thoughts of death or suicide.
In the new study, American investigators designed an experiment that exposed hamsters to different colors. The researchers chose hamsters because they are nocturnal, which means they sleep during the day and are active at night.
The animals were separated into 4 groups. One group of hamsters was kept in the dark during their nighttime period. Another group was placed in front of a blue light, a third group slept in front of a white light. While a fourth was put in front of a red light.
After four weeks, the researchers noted how much sugary water the hamsters drank. They found that the more depressed animals drank the least amount of water.
Randy Nelson heads the Department of Neuroscience at Ohio State University. He says animals that slept in blue and white light appeared to be the most depressed.
"What we saw was these animals didn't show any sleep disruptions at all but they did have mucked up circadian clock genes and they did show depressive phenotypes whereas if they were in the dim red light, they did not."
Randy Nelson notes that photosensitive cells in the retina, have little to do with eyesight. He says these cells send signals to the area of the brain that controls what has been called the natural sleep-wake cycle.
He says there's a lot of blue in white light, this explains why the blue light and white light hamsters appeared to be more depressed than the hamsters seeing red light or darkness.
Mr Nelson has suggestions for people who work late at night, or those who like to stay up late.
"My recommendation is if you are just living a typical mostly active [life] during the day, mostly inactive at night, you want to limit the exposure to TVs which are quite bluish in the light they give off and computer screens and things like that. You can get filtered glasses, you can get filters on your computer screen or your eReaders and that sort of thing to put it more in the reddish light."
The report on the effects of light on emotions was published in The Journal of Neuroscience.
You can read more health reports at our website testbig.com. And that's the Health Report from VOA Learning English, I'm Christopher Cruise.