Artificial nighttime lighting – from the dim glow of your iProduct to the alley streetlight – could be detrimental to your mental health.
Ohio State University Medical Center neuroscientists found that hamsters who slept 8 hours a night with a dim nightlight no longer enjoyed their old hamster games. The nightlight had altered the brain structure of these depressed rodents.
Many studies in the past, including some conducted by this team, have linked nighttime light pollution with health problems, including mood disorders, breast cancer, and significant weight gain.
At night, a gland in your brain secretes the hormone melatonin, which regulates light-related functions and biological rhythms – such as letting your body know when it's nighttime or what season it is. Exposure to light at night suppresses melatonin secretion, disrupting the body’s natural cycles.
The researchers kept one group of female Siberian hamsters (Phodopus sungorus) in a cycle of 16 hours of light followed by 8 hours of complete darkness. Another group had the same 16 hours of light, but slept 8 hours in dim lamplight – about as illuminated as a dark room with the TV on.
After several weeks, the researchers analyzed the hamsters for symptoms of depression, utilizing the same assessments pharmaceutical companies use to test antidepressive drugs in animals before testing on humans.
When the ‘dim’ hamsters were forced to swim, they spent less time performing an escape-directed swim, suggesting that they gave up sooner than the ‘dark’ hamsters. Dim hamsters were also less interested in drinking their sugar water treat; they were no longer getting the same "pleasurable and rewarding feeling” said co-author Tracy Bedrosian.
“Even dim light at night is sufficient to provoke depressive-like behaviors in hamsters,” Bedrosian concluded.
After processing the hamsters’ brains, the researchers found changes to the brain structure and chemistry of the depressed hamsters.
A part of their brain called the hippocampus had less dense networks of dendritic spines – the branchlike growths on brain cells responsible for transmitting messages between the cells. The hippocampus plays a key role in depressive disorders.
Nighttime low level lighting, according to the authors, may be a significant contributor to the increasing prevalence of mood disorders in North America and Europe. Additionally, the potential dangers of disrupted sleep would affect not only people who work at night, but also those who sleep with the lights on, fly frequently on red-eyes, and spend nights in hospitals.
If this link applies to humans, “people might want to think about getting dark shades," Bedrosian said, "and making sure to give themselves darkness when they go to sleep.”
Co-author Randy Nelson added: “You would expect to see an impact if we were blasting these hamsters with bright lights, but this was a very low level, something that most people could easily encounter every night.”
Image: Sleeping hamster by ASL via Flickr