Cross-sectional association between outdoor artificial light at night and sleep duration in middle-to-older aged adults: The NIH-AARP Diet and Health Study

Highlights

• Higher outdoor light at night (LAN) was associated with short sleep (<7 hours) in middle-to-older aged adults in the US.

• Higher LAN was associated with a decrease in the likelihood of reporting long sleep in men, but not in women.

• The associations between LAN and short sleep were larger in neighborhoods with higher levels of poverty.

Abstract

Introduction

Artificial light at night (ALAN) can disrupt circadian rhythms and cause sleep disturbances. Several previous epidemiological studies have reported an association between higher levels of outdoor ALAN and shorter sleep duration. However, it remains unclear how this association may differ by individual- and neighborhood-level socioeconomic status, and whether ALAN may also be associated with longer sleep duration.

Methods

We assessed the cross-sectional relationship between outdoor ALAN and self-reported sleep duration in 333,365 middle- to older-aged men and women in the NIH-AARP Diet and Health Study. Study participants reported baseline addresses, which were geocoded and linked with outdoor ALAN exposure measured by satellite imagery data obtained from the U.S. Defense Meteorological Satellite Program’s Operational Linescan System. We used multinomial logistic regression to estimate the multinomial odds ratio (MOR) and 95% confidence intervals (CI) for the likelihood of reporting very short (<5 h), short (<7 h) and long (≥9 h) sleep relative to reporting 7–8 h of sleep across quintiles of LAN. We also conducted subgroup analyses by individual-level education and census tract-level poverty levels.

Results

We found that higher levels of ALAN were associated with both very short and short sleep. When compared to the lowest quintile, the highest quintile of ALAN was associated with 16% and 25% increases in the likelihood of reporting short sleep in women (MOR_{Q1 vs Q5}, (95% CI), 1.16 (1.10, 1.22)) and men (1.25 (1.19, 1.31)), respectively. Moreover, we found that higher ALAN was associated with a decrease in the likelihood of reporting long sleep in men (0.79 (0.71, 0.89)). We also found that the associations between ALAN and short sleep were larger in neighborhoods with higher levels of poverty.

Conclusions

The burden of short sleep may be higher among residents in areas with higher levels of outdoor LAN, and this association is likely stronger in poorer neighborhoods. Future studies should investigate the potential benefits of reducing light intensity in high ALAN areas in improve sleep health.

Introduction

Nighttime outdoor lighting has permeated modern societies since the introduction of electric light. Hölker et al. estimated that outdoor artificial light at night (LAN) increased by 5–20% per year in many urban places throughout the second half of the 20th century (Hölker et al., 2010). A 2016 study reported that in the United States, nearly 80% of the population lived in areas where the natural appearance of the night sky could not be observed and nearly 40% lived in areas where night adaption of human eyes was inhibited by light (Falchi et al., 2016). Growing evidence suggests that the steady rise in the use of ALAN may have unintended health consequences, as multiple studies have linked ALAN with various diseases, including cancer (Garcia-Saenz et al., 2018; James et al., 2017), obesity (Koo et al., 2016), cardiovascular disease (Obayashi et al., 2015), and depression (Min and Min, 2018a). ALAN may suppress melatonin, a key hormone in circadian regulation, and enable nighttime activities that are misaligned with the internal circadian clock, while both melatonin suppression and misaligned nighttime activities may lead to sleep deficiency, an important risk factor for a wide range of health outcomes (Lunn et al., 2017).

Several epidemiological studies have reported a relationship between higher exposure to outdoor ALAN and sleep deficiency. In a study of more than 8,000 Korean adults, higher residential outdoor ALAN measured by satellite images was significantly associated with shorter sleep duration (Koo et al., 2016). Similarly, in another study using data from a representative sample of more than 19,000 American adults, outdoor ALAN was associated with higher likelihood of reporting <6 h of sleep (Ohayon and Milesi, 2016). However, neither study examined whether ALAN is associated with long sleep duration, a distinct risk factor for morbidity and mortality, especially in older adults. A recent systematic review and meta-analysis study found that long sleep duration was significantly associated with higher risks for all-cause mortality, mental disorders, type 2 diabetes, heart disease, stroke and obesity (Jike et al., 2018). Given the high prevalence of ALAN and myriad health problems associated with both short and long sleep, it is important to further evaluate the burden of short and long sleep associated with LAN.

Few studies examined whether the association between ALAN and sleep differ by other individual and environmental factors. Diez Roux and Mair hypothesized that high stress and lack of economic and psychosocial resources, conditions that are often associated with individual- and neighborhood-level disadvantages, may exacerbate the adverse effects of a harmful physical environment (Diez Roux and Neighborhoodshealth, 2010). Indeed, previous studies have consistently documented a higher prevalence of short sleep among people of low socioeconomic status (SES) (Grandner et al., 2016; Whinnery et al., 2014), and some studies also reported an association between long sleep and racial/ethnic minority and lower levels of education (Hale and Do, 2007; Cunningham et al., 2015). Moreover, several studies found that residents of low SES neighborhoods are more likely to experience short sleep than their counterparts living in high SES neighborhoods (Johnson et al., 2016a; Xiao and Hale, 2018). Individual- and neighborhoods-level disadvantage may be important modifiers of the relationship between ALAN on sleep; however, to the best of our knowledge, no study has directly examined this possibility.

These considerations motivate our present research. We studied outdoor ALAN in relation to both short and long sleep duration in more than 300,000 middle-to-older aged men and women in the NIH-AARP Diet and Health Study. We further investigated whether education (as an indicator of individual-level SES) and neighborhood poverty (as an indicator of neighborhood SES) modify the relationship between ALAN and sleep duration.