Outdoor artificial light at night linked to mood, mental disorders and sleep disruption in US teenagers: Study
Disturbances in daily rhythms of sleep and activity have long been observed in individuals with mental disorders, especially mood disorders. Now, researchers have found that teenagers 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 when compared to those who live in areas with low levels of night light.
Specifically, teenagers 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. According to the research team, 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, they emphasize.
"These findings illustrate the importance of joint consideration of both broader environmental-level and individual-level exposures in mental health and sleep research," says study author Dr Diana Paksarian in the analysis published in JAMA Psychiatry. She is a postdoctoral research fellow at the National Institute of Mental Health (NIMH), which is part of the National Institutes of Health. The research team also includes experts from Columbia University, Harvard Medical School, and Harvard TH Chan School of Public Health.
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. They are primarily driven by the light-dark cycle, which is the body's major source of information about the time of day, say experts. 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 among teens.
To understand this, the authors examined data from a nationally representative sample of adolescents in the US, 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 teenagers, in the 13 to 18 year age group.
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 teenagers 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 weekends.
To gauge the teenagers' exposure to outdoor artificial light at night, the authors used satellite imagery data to calculate the average artificial light levels for each census block group in the US. They found that levels of artificial light at night varied according to certain neighborhood-level factors, such as urbanicity, socioeconomic levels and population density.
The analysis reveals that 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 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). 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, say experts. The authors found that greater levels of artificial light at night were also associated with an increased likelihood of having a mood disorder or anxiety disorder.
"To our knowledge, this is the first study to report associations between outdoor artificial light at night (ALAN) and mental disorders among adolescents, associations that have potentially long-term implications for mental and physical health. Artificial light at night was positively associated with the prevalence of past-year mood and anxiety disorder. Adjusting for all covariates, each median absolute deviation increase in ALAN was associated with 1.07 times the odds of mood disorder and 1.10 times the odds of anxiety disorder," the authors write.
They add, "Further analyses revealed associations with bipolar disorder (odds ratio 1.19), specific phobias (odds ratio 1.18), and major depressive disorder or dysthymia (odds ratio 1.07). Among adolescent girls, differences in weeknight bedtime by ALAN (third and fourth quartiles versus the first quartile) were greater with increasing years since menarche."
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The study findings also highlight social disparities in exposure to artificial light, indicating that teenagers who belong to racial/ethnic minority groups, who come from immigrant families, or who come from families with lower income are more likely to live in areas with high levels of outdoor light at night. To the extent that exposure to artificial light disrupts daily rhythms such as sleep patterns, it could serve as an added stressor for teens who are already at increased risk for health problems due to social disadvantage, write experts.
Researchers say further studies are needed to evaluate the role of other contextual and individual-level risk factors in the association between artificial light at night and mental disorder. Future studies should elucidate whether public interventions designed to reduce the brightness or spectral composition of outdoor nighttime lighting could benefit mental and sleep health among youth, especially those who face other sources of social disadvantage, they suggest.
For example, studies investigating the effects of changes in street lighting could include health outcomes, such as sleep and mood, to weigh the benefits and perceived disadvantages of such interventions, they explain. "While environmental light exposure is only one factor in a more complex network of influences on sleep and behavior, it is likely to be an important target for prevention and interventions in adolescent health," says Dr Kathleen Merikangas, senior investigator and chief of the Genetic Epidemiology Research Branch at NIMH.