Beth Bradford
Sep 1, 2025
Research links Alzheimer’s, sundowning, and circadian rhythm disruptions, showing altered light sensitivity may fuel dementia symptoms.
Families of people with dementia (including my own) often encounter sundowning—a worsening of symptoms such as agitation, confusion, or restlessness that appear later in the day. Scientists believe these symptoms are linked to disruptions in circadian rhythms, the body’s internal clock that governs sleep-wake cycles.
Circadian rhythm disturbances not only worsen dementia symptoms but may also contribute to Alzheimer’s progression. During sleep, the brain clears toxic proteins like amyloid-β; poor sleep interferes with this clearance, potentially fueling disease development.
New Insights From Alzheimer’s Mouse Models
In a 2023 study published in Frontiers in Aging Neuroscience, researchers at the University of Virginia explored circadian behavior in two Alzheimer’s disease (AD) mouse models (3xTg and 5xFAD) compared to healthy mice. Here's what they found:
Faster circadian adjustment: Both Alzheimer’s mouse models adapted more quickly to a simulated “jet lag” (a 6-hour shift in light-dark cycles) than healthy mice. This was unexpected because circadian disruptions in humans with AD usually show up as sleep problems and sundowning symptoms.
Not linked to inflammation: The accelerated adjustment persisted even after microglia (immune cells in the brain often linked to inflammation) were depleted, suggesting other mechanisms were responsible.
Heightened light sensitivity: AD mice were unusually sensitive to dim light cues, with a greater number of melanopsin-positive retinal ganglion cells (ipRGCs) in their retinas. These light-sensing neurons may explain their rapid circadian shifts.
Why This Matters for Alzheimer’s and Dementia Care
“These data suggest that controlling the kind of light and the timing of the light could be key to reducing circadian disruptions in Alzheimer’s disease,” said study author and University of Virginia School of Medicine’s Heather Ferris, MD, PhD in a news release. “We hope that this research will help us to develop light therapies that people can use to reduce the progression of Alzheimer’s disease.”
While this research was conducted in mice, it highlights new ways circadian biology might influence Alzheimer’s disease:
Sundowning connection: Disrupted circadian rhythms may explain why symptoms intensify later in the day.
Light exposure as therapy: Since light plays a key role in circadian regulation, strategies like bright light therapy during the day and reduced nighttime light may help manage symptoms.
Early intervention: Because circadian disruptions appear early in Alzheimer’s, before memory loss, targeting them may offer a window for prevention or slowing progression.
The Takeaway
Alzheimer’s isn’t just about memory loss—it also deeply affects the body’s internal rhythms. This new study suggests that changes in light sensitivity and circadian control may underlie sundowning and sleep issues in dementia.
Supporting healthy sleep habits, maintaining consistent light schedules, and protecting circadian health could play an important role in both caring for loved ones with dementia and potentially reducing Alzheimer’s risk.