Here’s another reason to log off at a reasonable hour: exposure to dim lighting at night — such as that generated by a TV screen, computer or night-light — may lead to depressive symptoms, new animal research suggests.
A study from Ohio State University Medical Center found that hamsters with chronic exposure to dim light at night showed signs of depression within just a few weeks: reduced physical activity compared with hamsters living in normal light-dark conditions, as well as less interest in sugar water (a treat for the hamsters), greater signs of distress when placed in water, and changes in the brain’s hippocampus that are similar to brain changes seen in depressed people.
“The results we found in hamsters are consistent with what we know about depression in humans,” Tracy Bedrosian, the first author the on the new study, told reporters.
Mood disorders are by no means the only health condition linked to artificial lighting and screen time at night. Earlier this year, the American Medical Association (AMA) put out a disturbing summary of adverse health effects from nighttime lighting, noting that artificial lights disrupt circadian rhythms and alter the body’s normal hormonal responses. In particular, when people spend too little time in darkness, it seems that the body suppresses release of the hormone melatonin, which — among other things — is thought to fight tumor growth and cancers. Other health conditions affected by changes in circadian rhythms, according to the AMA report, may include obesity, diabetes and reproductive problems.
“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 minimizing their exposure to artificial light at night,” Bedrosian says. “That’s what the results we found in hamsters would suggest.”
Those animals’ depressive symptoms, at least, went away once the hamsters returned to a schedule that included eight full hours of total darkness per day.
Bedrosian and her colleagues say that, among humans, exposure to artificial lighting at night has surged over the past 50 years, a trend that happens to coincide with large increases in depression prevalence. Light pollution can come from TV and computer screens, other electronic displays and ambient sources such as streetlights, passing traffic and neighboring buildings, in addition to overhead lighting within the home.
For their study, the Ohio State researchers also investigated molecular mechanisms that may cause the brain changes associated with nighttime lighting. The scientists found that a cell-signaling protein, or cytokine, known as a hippocampal TNF (tumor necrosis factor) played a limited role. They demonstrated that by inhibiting TNF signaling, some of the depressive effects of light at night could be reversed in the hamsters. The results are published in the journal Molecular Psychiatry.