William Shakespeare once referred to stars as blessed candles of the night. I doubt that a modern interpretation of his “The Merchant of Venice” would so eloquently refer to televisions, computer screens, and nightlights that now illuminate what should be our darkest hours. And — alas — a new study finds that artificial light at night leads to symptoms of depression during the day.

The study, published in the journal Molecular Psychiatry, evaluated the effects of artificial light at night on hamsters. The hamsters exposed to the light showed depressive symptoms such as inactivity, increased anxiety, and less interest in treats. These symptoms are similar to those seen in humans with depression. Luckily, the effects on the hamsters could be reversed by eliminating the nighttime light.

Chronic artificial nighttime light has already been linked to an increased risk of breast cancer, obesity, and mood disorders, but the mechanism has not been clearly identified. In today’s world, we are surrounded by more sources of artificial light than natural light. While trying to make efficient use of our time and integrate technology into every waking (and sleeping) moment, darkness surrenders to e-readers in bed, late-night television, and smartphones never more than an arm’s reach away.

Hippocampal disorders are implicated in depression and disruptions of circadian rhythms — the body’s natural “clock.” And, most studies conclude that damage to the hippocampus is largely reversible when the offending stimuli are removed. This finding partially explains seasonal mood disorders with symptoms that come and go with the changes in hours of daylight and darkness.

The authors of the current study of hamsters are a long way from conclusive findings in humans. Still, our well-lit environment might warrant attention as a cause of the ever-growing presence of depression in westernized cultures. Unplugging your child’s nightlight that keeps monsters away might have detrimental effects on the whole family’s ability to get a good night’s sleep. But, do your best to unplug and spend a full night in total darkness…to sleep, perchance to dream.

References

Bedrosian TA, Fonken LK, Walton JC, Haim A, & Nelson RJ (2011). Dim light at night provokes depression-like behaviors and reduces CA1 dendritic spine density in female hamsters. Psychoneuroendocrinology, 36 (7), 1062-9 PMID: 21292405

Bedrosian TA, Weil ZM, & Nelson RJ (2012). Chronic dim light at night provokes reversible depression-like phenotype: possible role for TNF. Molecular psychiatry PMID: 22824811

Swaab DF, Bao AM, & Lucassen PJ (2005). The stress system in the human brain in depression and neurodegeneration. Ageing research reviews, 4 (2), 141-94 PMID: 15996533

Workman JL, Manny N, Walton JC, & Nelson RJ (2011). Short day lengths alter stress and depressive-like responses, and hippocampal morphology in Siberian hamsters. Hormones and behavior, 60 (5), 520-8 PMID: 21851822

Workman JL, Manny N, Walton JC, & Nelson RJ (2011). Short day lengths alter stress and depressive-like responses, and hippocampal morphology in Siberian hamsters. Hormones and behavior, 60 (5), 520-8 PMID: 21851822

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