The causes of depression are many and complex, but who'd have thought too much light could be part of the problem? Hamsters who sleep in total darkness are less susceptible to depression, and the same could be true of humans.Basking in the glow of your TV, smart phone or living room lights late into the night may put you at risk for depression, suggests a new study. **Exposure to dim lights when it should be dark may contribute to depression. **Light exposure at the wrong times of day has been linked to all sorts of health problems. **To boost your mood, it might help to give yourself some solid hours of true darkness at night.
The research, which involved hamsters, adds to growing evidence in both animals and people that exposure to even dim lights at night can lead to all sorts of negative health consequences, including breast cancer, sleep disorders and weight gain. Ohio State neuroscientist Tracy Bedrosian placed hamsters in one of two different environments. In the first, the hamsters spent 16 hours in daylight and then spent 8 hours in absolute darkness. The second group still got 16 hours of daylight, but their 8 sleeping hours were spent in the company of a dim light, roughly the equivalent of leaving one's TV on all night in an otherwise dark room.
Eight weeks later, Bedrosian tested the hamsters for signs of depression. The easiest way to spot depression in an animal like a hamster is see whether they demonstrate a preference for pleasurable treats like sugar water. The hamsters that spent 8 hours in total darkness showed a clear preference for sugar water over regular water, but the hamsters that slept with a dim light showed no preference at all. That suggests they're suffering from anhedonia, or an inability to feel pleasure, a key indicator of depression.Indeed, there were key differences in the brains of the two hamster groups. The hamsters that slept with the light had fewer dendritic spines, in the hippocampus area of brain. Dendritic spines are hair-like protrusions that brain cells use to communicate with one another. This ties in with human studies of depression that show the disease correlates with a shrinking of the hippocampus region.
Shown here is a PET scan revealing "hot spots"(orange-yellow areas) of increased activity in a non-depressed brain comparing a depressed brain and shrinkage in size of depressed brain.
Bedrosian suggests that these brain changes could be caused by a deficiency in the hormone melatonin. The hormone is essential in letting the body know that it's nighttime, but nearby light sources can reduce its production. Other studies have revealed melatonin's antidepressant qualities, which suggests a lack of it could spur on depression. This also fits neatly with studies demonstrating an increased risk of mood disorders for people who work at night.To explain how light exposure at night might affect the moods of both hamsters and people, the researchers turn to a hormone called melatonin. Our bodies start churning out the hormone as soon as we sense darkness, and its influence is broad. Among other roles, melatonin acts as an antioxidant. It regulates our circadian rhythms. It helps us fall asleep, and it controls the release of other hormones.With even a small amount of ambient light at night, the body might release the wrong amount of melatonin, or melatonin might get produced at the wrong time, leading to any number of problems, said neurologist Phyllis Zee, director of the Sleep Disorders Program at Northwestern University in Chicago. Studies have already implicated problems in the melatonin system with mood disorders, diabetes and sleep disturbances.
"They're all somehow related," Zee said, "and perhaps melatonin helps explain why there is this very strong relationship between depression, sleep, and circadian rhythms, as well as obesity and metabolism."
"Light affects so many biological systems," she added. "Light is a very powerful drug for the brain."
Major depression has grown more common in recent decades. And while there is probably no single reason for the trend, researchers suspect that light disturbances may play a part.
That suspicion is based, in part, on the simple observation that people today are exposed to far more sources of artificial light at night than they were 100 years ago. More people have computers in their bedrooms. More people fall asleep with the TV on.
Studies have also found that people who work night shifts have higher rates of mood disorders compared to people who sleep when their bodies are supposed to sleep.
It might be a good idea to avoid falling asleep with the TV or other light sources on. If nothing else, turning these off before you go to sleep will save on electricity bills, and that should be enough to buoy anyone's spirits.(Live Science)
