Sleeping with the blinds open could increase the risk of stroke by up to 43%, according to a study, the Daily Mail reports.
Many people keep the blinds open at night. Photo: Archive
Street lights and traffic pollution affect the body's natural sleep-wake cycle, and lack of rest puts stress on the heart and other organs.
Chinese researchers made this discovery after comparing data provided by thousands of people.
“Our study suggests that higher levels of exposure to outdoor artificial light at night may be a risk factor for cerebrovascular disease,” said Dr. Jain-Bing Wang, a public health specialist involved in the research.
“Therefore, we advise people, especially those living in urban areas, to consider reducing this exposure to guard against its potentially harmful impactWang added.
Many people are keeping the blinds open at night as part of a new wellness trend that encourages people to “wake up at the same time as the sun“.
But scientists point out that around 80% of the world's population already live in light-polluted areas – which could be causing them trouble falling asleep.
Using the Bortle Dark Sky Scale, which ranks the light level of the night sky from 1 to 9, scientists say a moonless night corresponds to level one, meaning very little light.
By comparison, big cities like New York come in at nine – suggesting high levels of light pollution.
For the study, published Monday, March 25, in the journal Stroke, scientists recruited 28,300 people from the Chinese port city of Ningbo, located about 193 km south of Shanghai.
Suppression of melatonin secretion
The participants were on average 62 years old and had no history of cerebrovascular disease – such as strokes and aneurysms.
They were followed for six years – from 2015 to 2021 – by scientists recording cases of stroke or other cerebrovascular diseases through hospital medical records.
They identified 1,278 cases in total, of which 900 were strokes.
To perform the analysis, satellite images were used to estimate the light pollution that each patient suffers from at night.
The results were adjusted for age, sex and income to suggest the risk of cerebrovascular disease from nighttime light exposure.
“Exposure to bright light at night could suppress melatonin secretion by the body's circadian rhythm“, the researchers said.
“This could lead to changes in biological markers, including high triglycerides… blood pressure and blood glucose, factors that trigger the onset of cerebrovascular disease”, the scientists also said.
Limitations of the study include the fact that there was no data on the participants' exposure to indoor light or whether they used curtains that did not allow light to enter the room.
The research was also conducted in part during COVID-19, which may have affected people's risk of disease through lifestyle changes.
The air pollution
The study also looked at the risk of cerebrovascular disease due to air pollution.
According to it, those living in areas with the highest levels of PM10 – a tiny compound released from car exhausts – had up to a 50% higher risk of cerebrovascular disease, compared to those exposed at the lowest levels.
Those exposed to the highest levels of PM2.5 had a 41% higher risk.
And those exposed to nitrogen oxide, released by cars and industrial areas, had a 31% higher risk.
The researchers said there was no link between air and light pollution and the risk of cerebrovascular disease.
Explaining the higher risk from air pollution in the study, they added: “A high risk of hemorrhagic stroke may be possible by causing arterial vasoconstriction, high blood pressure and increased susceptibility to cerebral vascular rupture by triggering endothelial dysfunction“.
