Says the study: Room darkness can affect health

Every day, once sunlight falls to people's eyes, trillions <x0 biological” are restored into human cells.

The human body uses light to regulate many vital processes with accuracy - from the production of enzymes in the liver, to the separation of hair cells, and to maintain blood pressure to healthy levels. When people fail to get enough light at the right time of the day, their health may deteriorate, it has written T TIMES.

In addition to the benefits, however, researchers are increasingly discovering that there are dark edges, especially at night.

Various studies have shown that exposure to light during sleep is linked to serious health problems.

In 2019 a study found links between obesity and light during sleep.

Another study linked light during the night with high blood pressure, obesity, and diabetes among the elderly.

And a study published in October 2025, which examined the exposure data through a monitoring device that is placed on the wrist of the hand, which some 90 thousand people held, has found that nighttime light was linked to higher risk of heart failure and other cardiovascular diseases over about 10 years.

Why such studies cannot prove directly that light is the cause, they show ever more clearly that good health requires dark nights.

“The latest study was based on the largest database for personal exposure to light, part of UK Biobank”, explained Angus Burns, a researcher at Harvard Medical School and author of the study.

UK Biobank includes data from half a million volunteers, many of whom have kept monitoring equipment on the wrist for a week.

These devices also had light sensors.

When I realized this, I thought if we could get the data out, we'd have a record minute after minute of light that people experienced,” says Burns. Extracting data was difficult, but the result showed clear differences between day and night.

What did researchers discover?

When people were divided into groups according to the amount of light between midnight and 6: 00 a.m., it was found that about half were sleeping in total darkness. The other half, however, was exposed to light. At 10 percent of the highest exposure, the average light level was about 100 luxury (the size of light measurement), about the size of a poorly lit hotel corridor.

This could happen because the television was still on or because people stayed up late.

Compared to those sleeping in the dark, the most enlightened nights were more likely to develop heart disease or have a heart attack in the years to come. The more light at night, the higher the risk. People in the 10 percent most exposed had greater risk of aerial fibrillation and stroke.

Even after factors such as body weight, potential diabetes, and other health problems were considered, the risk remained 30 to 60 percent higher, depending on the disease. This suggests that light has a direct effect.

It wasn't just a matter of bad sleep. Even after we adjusted to the amount of sleep, exposure to light remained a strong and independent predictor of heart disease”, said Daniel Windright, coauthor of the study.

These findings match previous studies. UK Biobank research confirms this link to a much larger number of people”, Dr. Phyllis Zee, professor of neurology at Northwestern University, said.

Why is light harmful at night?

Biological intervention may be one reason, curbing the production of melatonin, the hormone that distinguishes day from night. Short flashes of light can also halt its production.
“From an evolutionary point of view, we are gaining light at night many times stronger than the light of the moon or of the fire”, Burns said.

Meanwhile, during the day most people spend their time inside, receiving far less natural light than the body needs.

Researchers found that the very bright days and very dark nights can protect you from heart problems.

lab experiments have shown that light - sleeping people have higher heart rates during sleep and more metabolicism the following day.

It was as if the body was in a constant state of alarm”, Zee explained.

Experts have suggested simple measures such as using eye masks, dark curtains, or closing light sources at night to lower exposure.

Electrical change is completely unnatural for our biology. On the evolutionary scale, it's very new. The ancient man did not sleep at midnight surrounded by light. Probably not”, Burns said./Periscopi/