VANCOUVER—People who live in areas with more intense outdoor nighttime light radiance are more likely to go to bed after midnight, get fewer than six hours of sleep, and be dissatisfied with their sleep, compared with people who live in areas with less intense nighttime light radiance, according to research presented at the 68th Annual Meeting of the American Academy of Neurology. Outdoor lights, such as streetlights, allow people to be more active at night and increase safety and security. With intense outdoor light, however, "the transition between the day and the evening doesn't exist any more," said Maurice M. Ohayon, MD, DSc, PhD, Chief of the Division of Public Mental Health and Population Sciences and Director of the Stanford Sleep Epidemiology Research Center at Stanford University in California. "The concern is that we have reduced our exposure to darkness, and it could be affecting our sleep."
To evaluate the association between nighttime light intensity and sleep habits in the American population, Dr. Ohayon and colleagues conducted a study using telephone interviews with 15,863 adults in 15 states. Interviews were conducted between 2002 and 2009 using the Sleep-EVAL artificial intelligence system. Researchers also recorded each interviewee's longitude and latitude.
The investigators then obtained the outdoor nighttime light radiance for each participant's surrounding area from the Defense Meteorological Satellite Program's Operational Linescan System.
Compared with people living in areas with less intense nighttime light, people living in areas with more intense nighttime light were more likely to be dissatisfied with their sleep quantity or quality (29% vs 16%), report fatigue (9% vs 7%), and experience confusional arousals (19% vs 13%). In addition, they slept less per night on average (402 minutes vs 412 minutes).
The investigators used logistic regression to control for noise and other factors related to urban life, Dr. Ohayon said. The researchers plan to evaluate the relationship between light radiance and mood disorders in future studies.
"Outdoor nighttime light exposure is strongly associated with changes in sleep habits and impacts our daytime functioning, increasing the risks of excessive sleepiness," concluded the researchers. "If this association is confirmed by other studies, people may want to consider room darkening shades, sleep masks, or other options to reduce their exposure," Dr. Ohayon said.