Sleeping with a small light on or leaving the television on standby may seem harmless. However, recent work suggests that this nocturnal exposure could disrupt our biological clock and, in the longer term, be linked to the mechanisms involved in Alzheimer’s disease.
Many of us grew up with a night light for reassurance. But this habit, sometimes carried into adulthood because of a television on, a telephone or a light coming from the hallway, could have unsuspected effects on the quality of sleep.
Sleep plays an essential role in the proper functioning of the body. However, researchers from the University of Kentucky were interested in the impact of nighttime light on our circadian rhythm, this internal clock which notably regulates sleep-wake cycles.
Weak light is enough to disrupt the biological clock
A first study, published in the journal SLEEP, analyzed the effects of low exposure to light during the night, such as that emitted by a television, a telephone, a lamp or even hallway lighting.
Researchers observed, in animal models, that even low-intensity light reduced the stability of circadian rhythms and increased their fragmentation. In animals with Alzheimer’s disease, this nocturnal exposure was also associated with a slight increase in amyloid, a protein linked to this pathology, as well as changes in the activity of microglia, the brain’s immune cells.
“These studies examine why sleep and daily biological rhythms are disrupted in Alzheimer’s disease, and whether these disruptions are influenced by both the external environment and inflammation inside the brain” says Adam Bachstetter, lead author of the study and associate professor of neuroscience at the University of Kentucky College of Medicine.
An editorial published alongside the study in the journal SLEEP also highlights that artificial nighttime light could constitute a modifiable environmental factor likely to influence the risk or progression of Alzheimer’s disease via circadian and neuroimmune mechanisms.
Sleep may play a role in Alzheimer’s progression
A second study, published in the journal Alzheimer’s & Dementiasheds another light. The researchers report that sleep disorders and the fragmentation of circadian rhythms appear in the forties.
The team then tested the compound MW151, which targets excessive inflammatory signaling in glial cells in the brain. The results show an improvement in sleep patterns and a restoration of daily rhythms, without a reduction in amyloid accumulation. These observations suggest that brain inflammation may be an important factor in the sleep disturbances observed in Alzheimer’s disease.
For Adam Bachstetter, these results remind us that “Poor sleep quality is not just a symptom that appears late in the disease. It may interact with amyloid pathology, microglial function and inflammation in ways that influence disease progression“.
This work also reinforces the recommendations already known for preserving quality sleep. As Marilyn Duncan, professor of neuroscience and co-author of the study, points out, reducing unnecessary exposure to light at night, maintaining a regular sleep schedule, and promoting healthy circadian rhythms are simple, low-risk strategies.
Concretely, closing your shutters and curtains correctly, turning off the screens and sleeping in complete darkness could help preserve the quality of sleep.