Exposure to dim light at night causes depression among hamsters and even humans, but the harmful effects of the lights could be reversed by simply returning to standard light and dark cycle.
Researchers from Ohio State University have found a way to reverse symptoms of depression caused by dim light by just returning to normal light and dark cycle. The discovery was made while studying the behaviour of groups of Serbian hamsters exposed to various lights.
"The good news is that people who stay up late in front of the television and computer may be able to undo some of the harmful effects just by going back to a regular light-dark cycle and minimising their exposure to artificial light at night," said Tracy Bedrosian, doctoral student in neuroscience at Ohio State University, in a statement.
Researchers had conducted an experiment on two groups of hamsters. During the study, one group of hamsters was exposed normal day and night light setting - 16 hours of daylight and eight hours of total darkness for eight weeks. The other group was exposed to 16 hours of normal daylight and eight hours of dim light for four weeks. Then they conducted several behavioural tests.
The study found that hamsters exposed to dim light also showed greater depressive symptoms such as less interest in drinking sugar water that they usually enjoy compared to the other group.
Then these hamsters were moved back to a standard light cycle for a few weeks before testing began. Researchers found that within a few weeks after returning to normal lighting cycle, the hamsters exposed to dim light showed no more symptoms of depression.
To know exactly how light affected the brain, researchers studied changes in the brain that had occurred after the hamsters were exposed to dim light.
The study found TNF, a particular protein in the brain of hamsters and in humans. They believed that the TNF protein could play a major role in how light at night leads to depression
TNF is one of a large family of proteins called cytokines, chemical messengers that are mobilised when the body is injured or has an infection. These cytokines cause inflammation in their effort to repair an injured or infected area of the body. However, this inflammation can be damaging when it is constant, as happens in hamsters exposed to dim light at night, according to a Eurekalert.org report.
Researchers conducted another experiment: a group of hamsters was given a drug called XPro1595, a TNF inhibitor that blocks the effects of TNF in the brain, and then the hamsters were exposed to dim light.
The study found that hamsters which consumed XPro1595 drug had no symptoms of depression. This clearly shows that by blocking the TNF protein or just simply returning to standard light and dark cycle reduces of the symptoms of depression.
"These findings add to the growing evidence that suggest chronic exposure to artificial light at night may play some role in the rising rates of depression in humans during the past 50 years, said Bedrosian."The results we found in hamsters are consistent with what we know about depression in humans. "