A new Northwestern Medicine study on senior citizens, both men and women in ages 63 to 84, has found that people exposed to any amount of light while sleeping at night are more likely to be obese and have high blood pressure and diabetes compared to adults, who were not exposed to any light during the night. The study was published in the journal SLEEP on June 22.
The study says that even low light can disturb sleep, increasing the risk of serious health problems. “Whether it be from one’s smartphone, leaving a TV on overnight or light pollution in a big city, we live among an abundant number of artificial sources of light that are available 24 hours of a day,” said the study’s corresponding author Dr Minjee Kim, assistant professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “Older adults already are at higher risk for diabetes and cardiovascular disease, so we wanted to see if there was a difference in frequencies of these diseases related to light exposure at night.”
Light exposure in the study sample was measured with a wrist-worn device and tracked over seven days.
Study investigators were surprised to find that less than half of the 552 study participants consistently had a five-hour period of complete darkness per day. The rest of the participants were exposed to some light even during their darkest five-hour periods of the day, usually in the middle of their sleep at night.
As this was a real-world, cross-sectional study, investigators do not know if obesity, diabetes and hypertension cause people to sleep with a light on, or if the light contributed to the development of these conditions.
People in the studies age group also are more likely to use the bathroom in the middle of the night or another reason to keep the light on. Someone with foot numbness because of diabetes may want to keep a night light on to reduce the risk of falls.
However, it is still important for people to avoid or minimise the amount of light exposure during sleep, insisted senior study co-author Dr Phyllis Zee, chief of sleep medicine at Feinberg and a Northwestern Medicine physician.
The team of researchers is considering an intervention study to test whether restoration of the natural light-dark cycle improves health outcomes such as cognition.