Exposure to dim light at night increases depressive-like behaviors in offspring, study finds

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Being exposed to artificial lighting at night appears to not only impact animals, but their offspring as well. New research has found that depressive-like behaviors are elevated among the offspring of hamsters exposed to dim light at night.

If the findings translate to humans, it could help explain the rising rates of depression in the industrialized world, according to the researchers from Ohio State University Wexner Medical Center.

“Work from our lab and epidemiological studies suggest that disruption of the circadian system through exposure to light at night has detrimental effects on physiology and behavior,” explained researcher Yasmine Cisse, a graduate student who has published several studies on the effects of dim light at night.

“Specifically, exposure to light at night increases depressive-like behaviors in rodents, is associated with increased rates of depression in humans, and alters rhythms in hormones such as melatonin and glucocorticoids, which have important roles in modulating emotional affect.”

“Endocrine disrupting chemicals (EDCs) have gained a lot of attention recently due to their ability to alter behavior across multiple generations without re-exposure. I was interested in investigating whether the endocrine disruption induced by light at night would have the same transgenerational capacity as EDCs,” Cisse told PsyPost.

The new study, which was recently published in the scientific journal Psychoneuroendocrinology, provides evidence that exposure to light at night affects the offspring of rodents as well.

The researchers found that the offspring of Siberian hamsters were more likely to exhibit depressive-like behaviors when their parents had been exposed to nighttime lighting for 9 weeks before mating, compared to offspring whose parents were exposed to standard dark night conditions.

“We used 5 lux of nighttime lighting in this study, which is equivalent to a night light about 3 feet (1 meter) from your face and much less than the 150-300 lux coming off of a phone or iPad screen,” Cisse noted. “Siberian hamsters are nocturnal. We used a nocturnal rodent to separate the effects of circadian disruption from sleep disruption, which is also known to alter mood.”

The offspring of hamsters exposed to nighttime lighting also showed changes in their neuroendocrine system.

“The major takeaway from this is to maintain good circadian hygiene throughout life,” Cisse said. “It is important to keep your nighttime environment as dark as possible, but also to get sufficient sunlight during the day to provide clear signals of day and night to the circadian system. This practice not only affects your health, but as we are now learning, can have consequences on future generations.”

Humans, of course, are not rodents. But we do share many of the same basic biological structures and functions. Nevertheless, the findings still need to be replicated with a human sample.

“The results of previous studies on light at night in rodents have mirrored the increased weight gain, depression, and increased susceptibility to cancer seen prominently in night shift workers but also now observed in the general population exposed to nighttime electric lighting. Given this correlation in previous studies it is tempting to extrapolate these second generation results, but this has not yet been investigated in humans,” Cisse told PsyPost.

“As the night shift workers may serve as ‘canaries in a coal mine’ for the health problems associated with dysregulation of circadian rhythms via light at night, studies in rodents provide a cautionary tale of the health effects of light at night both directly and now transgenerationally.”

The study, “Depressive-like behavior is elevated among offspring of parents exposed to dim light at night prior to mating“, was also co-authored by Kathryn L.G. Russart and Randy J. Nelson.

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