The relationship between sleep status and cardiovascular health has long been viewed primarily through the lens of sleep duration and noise levels. However, in recent years, the attention of researchers has increasingly attracted another factor – night lighting in the bedroom. Rambler will tell you what new scientific data has shown.
Light at night is a cardiovascular risk factor
Artificial light at night disrupts circadian rhythms – internal biological clocks that regulate sleep, hormone balance, blood pressure and metabolism. Melatonin, a hormone produced in the dark, plays an important role in this process. Its decline is associated not only with poorer sleep but also with increased activity of the sympathetic nervous system, which causes stress reactions.
Increased lighting levels at night keep the body in a “combat ready” state even while sleeping. This is accompanied by an increase in heart rate, fluctuations in blood pressure and activation of inflammatory processes that cause atherosclerosis.
New research data
A new study conducted by US scientists and presented at the American Heart Association's annual meeting in November 2025 provides some of the strongest evidence yet of this link. The study involved 466 adult residents of Boston who were not diagnosed with cardiovascular disease or an active cancer process at the start of observation.
A special feature of the study is the use of neuroimaging. Light levels in the participants' homes were compared with data from PET/CT scans, which assessed the activity of certain brain regions related to stress, as well as the level of inflammation in artery walls.
The year of discovery in 2025 will change medicine
The results are published in News roomfound that people who slept at higher levels of nighttime light had:
- increased activity in brain regions involved in stress response;
- increased inflammatory processes in blood vessels;
- The combination of factors is directly related to the development of myocardial infarction and stroke.
According to lead researcher Shady Abohashema, even a slight increase in lighting in the bedroom can trigger the central nervous system's stress response. The brain perceives light as a signal of alertness, interrupting the body's normal nighttime “switch” into recovery mode.
Activation of stress centers leads to the release of hormones such as cortisol and adrenaline. These substances increase vascular inflammation, promote endothelial damage, and facilitate the accumulation of atherosclerotic plaques. Over time, this process increases the likelihood of chronic cardiovascular disease.
Scientists stress that this is not just about bright light. Even a running TV, a streetlight outside the window, a nightlight or an electronic device screen can create enough light levels to disrupt physiological processes.
How much does the risk increase?
Research shows a quantitative link between light levels at night and future heart problems. Each standard deviation increase in light levels during sleep is associated with:
- The risk of cardiovascular disease increases by 35% in the next 5 years;
- growth risk of 22% in the next 10 years.
Importantly, this correlation persisted even after controlling for other factors: noise, income, housing density, air quality and socioeconomic conditions.
Increase efficiency in stressful environments
Additional analysis shows that the harmful effects of nighttime light are increased in people living under conditions of increased stress. Then, night light does not act in isolation, but is applied to the already loaded nervous and cardiovascular systems. As a result, the inflammatory process develops faster and the body's compensatory mechanisms are exhausted.
Practical recommendations
Based on the data obtained, the researchers recommend:
- Darken the bedroom as much as possible at night;
- Avoid using devices before bed;
- Use thick curtains or blinds;
- If necessary, wear a sleep mask;
- Choose lights with screens, motion sensors and directional lighting;
- Eliminate constant background light sources from vision at night.
In recent years, there has been growing evidence that nighttime light affects not only sleep but also metabolism, glucose levels, blood pressure and chronic inflammation. This study is one of the first to clearly show how nighttime light through brain mechanisms can trigger pathological processes in blood vessels.
Previously, we wrote about who sleep-deprived people are and how they can get four hours of sleep a day.
