Watching television late into the night could make you depressed

Researchers found that too much artificial light at night can alter mood and lead to similar symptoms to depression such as lack of energy and enthusiasm.

The team from Ohio State University believe the connection could explain why levels of depression have increased as the use of electric lights have increased.

The "blue light" from televisions could be especially disruptive.

The psychologists found that mice housed in a lighted room 24 hours a day exhibited more depressive symptoms than did similar mice that had a normal light-dark cycle.

The results suggest that more attention needs to be focused on how artificial lighting affects emotional health in humans, according to study co-author Professor Randy Nelson, a professor of neuroscience and psychology.

"The increasing rate of depressive disorders in humans corresponds with the increasing use of light at night in modern society," he said.

"Many people are now exposed to unnatural light cycles, and that may have real consequences for our health."

The study, which will appear in the journal Behavioural Brain Research, involved mice who were subjected to varying degrees of light at night.

The rodents subjected to the most artificial light were found to be the most depressive using tests used by pharmaceutical companies to test anti-depressive and anti-anxiety drugs in animals before they are used in humans.

The researchers believe that the findings do apply to humans.

"This is important for people who work night shifts, and for children and others who watch TV late into the night, disrupting their usual light-dark cycle," said Laura Fonken, lead author at Ohio State University.

She said that the ability to escape light did help remove the symptoms.

There are many other practical implications. Nelson noted that most intensive care units are brightly lit all night long, which may add to the problems of their patients.

"Light at night has significant social, ecological, behavioural, and health consequences that are only now becoming apparent,"said Professor Nelson.

"We suspect that suppression of melatonin may be involved in the effects of light at night on depressed affect. Blue light is especially good at suppressing melatonin so watching TV at night may reduce the nocturnal rise in melatonin."