A recent review published in Medscape compiles a series of studies from recent years, and raises a worrying but important message: exposure to artificial light before and during sleep at night – from screens, household lamps and street lights – It impairs sleep quality and may also harm heart health and mood, disrupt metabolism, and over time, harm brain health..

What did they investigate?
The various studies examined how exposure to light in the evening and at night affects the body's biological clock, sleep quality, and other body systems. Some studies followed tens of thousands of people for years using light sensors, and others examined under laboratory conditions what happens after one night of sleeping in a lit room. At the same time, the connections between exposure to light at night and mental state, metabolic function, and indicators that may also be relevant to brain aging were also examined.

What did they find?
Light at night disrupts the circadian rhythm – the “internal clock” that synchronizes sleep, hormones, blood pressure, metabolism and brain function. Even one night of sleeping in moderate light tends to increase the heart rate during the night and disrupt blood sugar balance the next morning. A large study that compared high and moderate light exposure during the night found a higher risk of cardiovascular disease in the group of participants who were exposed to high light during nighttime sleep. Another study found that exposure to light at night is associated with more depression, anxiety, psychosis and bipolar disorder. There is no clear evidence to date that exposure to light during nighttime sleep directly causes dementia, but evidence is accumulating that exposure to light during sleep disrupts the quality of nighttime sleep and the biological clock, increases inflammation components and, as a result, impairs brain function.

What are the conclusions?
Exposure to light during sleep preparation and during the night is not only a nuisance that makes it difficult to fall asleep, but also a modifiable environmental factor that may affect the health of the brain and the whole body. For those interested in reducing the risk of cognitive decline and dementia, this is an important message: maintaining darkness during sleep at night and exposure to daylight during the day may protect the brain and cognitive health.

What are the recommendations for the public?
Get exposed to natural daylight as early as possible in the morning. Dim the lights after sunset. Reduce screens before bed. Keep your bedroom as dark as possible. If you get up at night, use dim, focused lighting, and don’t turn on the lights throughout the house. These are simple, non-drug steps that may improve sleep – and may also contribute to brain health in the long term.

The main message from the studies:
Exposure to light at night is not just a matter of comfort or sleep habits. More and more research suggests that darkness at night and daylight in the morning are important parts of maintaining a healthy body and brain.

The full article:

• Link:
  https://www.medscape.com/viewarticle/how-nighttime-light-quietly-became-serious-health-threat-2026a10005w7
• Reference:
  Pajer, N. (2026, February 25). How nighttime light quietly became a serious health threat.