Editor’s Note: Sign up for CNN’s Sleep, But Better newsletter series. Our seven-part guide contains useful tips for sleeping better.
Sleeping in a room exposed to outdoor artificial light at night may increase the risk of developing diabetes, according to a study of nearly 100,000 Chinese adults.
According to the study published Tuesday in the journal Diabetologia, people who lived in areas of China with high light pollution at night were about 28% more likely to develop diabetes than people who lived in the least polluted areas.
Ultimately, more than 9 million cases of diabetes in Chinese adults aged 18 and older may be due to outdoor light pollution at night, the authors said, and the number is likely to increase as more people move to cities.
However, a lack of darkness affects more than urban areas. Urban light pollution is so pervasive that it can affect suburbs and forest parks that may be tens, even hundreds, of miles from the light source, the authors said.
“The study confirms previous research on the potential adverse effects of light at night on metabolic function and risk of diabetes,” said Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine in Chicago, who was not involved in the study
Previous research has shown an association between artificial light at night and weight gain and obesity, disturbances in metabolic function, insulin secretion and the development of diabetes, and cardiovascular risk factors.
An investigation published earlier this year by Zee and her team investigated the role of light in sleep for healthy adults in their 20s. Sleeping just one night with dim lights, such as a TV with the sound off, increased the young people’s blood sugar and heart rate during the sleep lab experiment.
In previous studies, increased heart rate at night has been shown to be a risk factor for future heart disease and premature death, while higher blood sugar levels are a sign of insulin resistance, which can eventually lead to type 2 diabetes.
“Healthy sleep is extremely important in preventing the development of diabetes,” says Dr. Gareth Nye, senior lecturer in physiology at the University of Chester in the UK. He was not involved in the Diabetologia study.
“Studies have suggested that inconsistent sleep patterns have been linked to an increased risk of type 2 diabetes,” he said in a statement.
The new study used data from the 2010 China Noncommunicable Disease Surveillance Study, which asked representative samples of China’s population about social demographics, lifestyle factors, and medical and family health histories. Blood samples were collected and compared to satellite images of light levels in the area of China where each person lived.
The analysis found that chronic exposure to light pollution at night increased blood glucose levels and led to a higher risk of insulin resistance and diabetes.
However, a direct link between diabetes and nighttime light pollution is still unclear, as living in an urban area itself is a known contributor to the development of diabetes, Nye explains.
“It has long been known that living in (a) urbanized area increases the risk of obesity due to greater access to high-fat and convenience foods, less physical activity due to transportation links, and less social activity,” Nye wrote.
Strategies to reduce light levels at night include moving your bed away from windows and using light-blocking blinds. If the light stays low, try a sleep mask to protect your eyes.
Be aware of the type of light you have in your bedroom and ban all lights in the blue spectrum, such as those emitted by electronic devices such as televisions, smartphones, tablets and laptops — blue light is the most stimulating type of light, Zee said.
“If you need to have a lamp on for safety reasons, change the color. You want to choose lamps with more reddish or brownish tones,” she said. If a nightlight is needed, keep it dim and at floor level so it’s more reflected instead of next to your eye at bed level, she suggested.
Don’t sleep with the television on — if you have a tendency to fall asleep with it still on, put it on a timer, Zee suggested.
Dim the ambient light at night for at least two to three hours before bed, and if you “absolutely have to use computer or other light-emitting screens, change the wavelength of the screen light to longer orange-orange,” Zee said. “Important, provide light during the day – daylight is healthy!”