Those whose chosen method of relaxation is late-night TV may want to turn in their remotes. Recent research shows that too much light at night can lead to symptoms of depression. The research was presented October 21 at the annual meeting of the Society for Neuroscience in Chicago and will appear in the December 28 edition of the journal of Behavioural Brain Research. The researchers found that mice exposed to light 24 hours a day showed more depressive symptoms than mice with a normal light-dark cycle. Mice that lived in constant light but that had the ability to escape to a dark opaque tube showed less evidence of depressive symptoms. Laura Fonken, the lead author of the study said, “The ability to escape light seemed to quell the depressive effects. But constant light with no chance of escape increased depressive symptoms.” Fonken is a graduate student in psychology at Ohio State University. Co-author Randy Nelson, a professor of neuroscience and psychology at Ohio State said that the results show that artificial lighting may affect the emotional health of humans too. “The increasing rate of depressive disorders in humans corresponds with the increasing use of light at night in modern society. Many people are now exposed to unnatural light cycles and that may have real consequences for our health.” People exposed to unnatural light cycles include not only third-shift workers and those who watch late-night TV, but also patients in such situations as intensive care units. The study included 24 male laboratory mice. Twelve of the mice were exposed to light 16 hours a day and darkness for the other eight hours. The other twelve mice were exposed to 24 hours of light. Half of each group had an opaque tube to escape the light, while the other half had only a clear tube that allowed light in. The study examined levels of both depression and anxiety in the animals. Surprisingly, the mice housed in constant light showed lower levels of anxiety. The mice also showed lower levels of corticosterone, which is a stress hormone associated with anxiety. In some of the tests, the mice that were given opaque tubes to escape the light when they wanted to exhibited no more depressive signs than the mice that were exposed to normal light-dark cycles. The researchers were surprised to see that while depression symptoms for complete light-exposed mice were higher, their anxiety symptoms were no more active than those mice given normal light-dark cycles. The researchers were surprised with the results because in humans anxiety and depression symptoms are often linked. The study provides important information for those affected by artificial light at night. The additional evidence supports past research that the use of artificial light at night may have harmful effects on health.
