Study shows associations between outdoor, artificial light and health outcomes

Adolescents who live in areas that have high levels of artificial light at night tend to get less sleep and are more likely to have a mood disorder relative to teens who live in areas with low levels of night-time light, according to a new study by the National Institute of Mental Health (NIMH), part of the National Institutes of Health, and is published in the journal JAMA Psychiatry.

Daily rhythms, including the circadian rhythms that drive our sleep-wake cycles, are thought to be important factors that contribute to physical and mental health. The presence of artificial light at night can disrupt these rhythms, altering the light-dark cycle that influences hormonal, cellular, and other biological processes. Researchers have investigated associations among indoor artificial light, daily rhythms, and mental health, but the impact of outdoor artificial light has received relatively little attention, especially in teens.

For the study, researchers examined data from a nationally representative sample of adolescents in the United States, which was collected from 2001 to 2004 as part of the National Comorbidity Survey Adolescent Supplement (NCS-A). The dataset included information about individual-level and neighborhood-level characteristics, mental health outcomes, and sleep patterns for a total of 10,123 teens, ages 13 to 18 years old.

As part of in-person interviews for the NCS-A, the adolescents completed a validated assessment to determine whether they met the diagnostic criteria for various mental disorders. The teens also answered questions about their sleep habits, reporting what time they usually went to bed and how many hours of sleep they usually got on weeknights and on weekends.

To gauge the teens' exposure to outdoor artificial light at night, the researchers used satellite imagery data to calculate the average artificial light levels for each census block group in the U.S. As expected, levels of artificial light at night varied according to certain neighborhood-level factors, such as urbanicity, socioeconomic levels, and population density.

The researchers found teens who lived in areas with high levels of artificial light at night tended to report later weeknight bedtimes and shorter weeknight sleep duration. This association held even after the researchers accounted for various individual-level factors (such as age, sex, race/ethnicity, number of siblings, parental education) and neighborhood-level factors (such as county-level urbanicity and population density). The analyses showed that, on average, teens in areas with the highest levels of outdoor light went to bed about 29 minutes later and got 11 fewer minutes of sleep than did teens in areas with the lowest levels.

The data showed that greater levels of artificial light at night were also associated with increased likelihood of having a mood disorder or anxiety disorder. Specifically, teens who lived in areas with higher levels of artificial light at night were more likely to meet the diagnostic criteria for bipolar disorder or specific phobia.

Diana Paksarian, PhD, study authors and a postdoctoral research fellow at NIMH, this association is noteworthy because disruptions to sleep and circadian rhythms is a well-documented feature of certain mental disorders, including bipolar disorder. The study findings point to disrupted sleep as a possible link between artificial nighttime light exposure and mental health outcomes, a link that should be tested in future prospective research.