Environmental Influences on Sleep in the California Teachers Study Cohort

Charlie Zhong; Travis Longcore; Jennifer Benbow; Nadia T. Chung; Khang Chau; Sophia S. Wang; James V. Lacey, Jr.; Meredith Franklin

Disclosures

Am J Epidemiol. 2022;191(9):1532-1539. 

In This Article

Abstract and Introduction

Abstract

Only two-thirds of Americans meet the recommended 7 hours of sleep nightly. Insufficient sleep and circadian disruption have been associated with adverse health outcomes, including diabetes and cardiovascular disease. Several environmental disruptors of sleep have been reported, such as artificial light at night (ALAN) and noise. These studies tended to evaluate exposures individually. We evaluated several spatially derived environmental exposures (ALAN, noise, green space, and air pollution) and self-reported sleep outcomes obtained in 2012–2015 in a large cohort of 51,562 women in the California Teachers Study. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for sleep duration and latency. After adjusting for age, race/ethnicity, chronotype, use of sleep medication, and self-reported trouble sleeping, ALAN (per 5 millicandela (mcd)/m2 luminance, OR = 1.13, 95% CI: 1.07, 1.20) and air pollution (per 5 μg/m3 PM2.5, OR = 1.06, 95% CI: 1.04, 1.09) were associated with shorter sleep duration (<7 hours), and noise was associated with longer latency (>15 minutes) (per 10 decibels, OR = 1.05, 95% CI: 1.01, 1.10). Green space was associated with increased duration (per 0.1 units, OR = 0.41, 95% CI: 0.28, 0.60) and decreased latency (per 0.1 units, OR = 0.55, 95% CI: 0.39, 0.78). Further research is necessary to understand how these and other exposures (e.g., diet) perturb an individuals' inherited sleep patterns and contribute to downstream health outcomes.

Introduction

Disruptions in sleep have been associated with increased risk of several health conditions, including cardiovascular disease, diabetes, and cancer.[1] In 2015, the American Academy of Sleep Medicine and Sleep Research Society published a joint consensus statement recommending that adults get at least 7 hours of sleep each night;[2] however, 35% of American adults fall short of this recommendation.[3]

Light is one of the main environmental factors affecting the sleep-wake cycle. Photosensitive cells in our retina respond to light and trigger the suprachiasmatic nucleus in the hypothalamus. The suprachiasmatic nucleus then modulates body temperature and regulates levels of cortisol and melatonin in response to the amount of light we perceive. The reduction of exposure to light at night triggers the increase in melatonin, leading to the feeling of sleepiness. Exposure to bright lights before sleep can delay the release of melatonin, therefore increasing sleep latency and disrupting circadian rhythm.[4] While the direct stimuli of light indoors prior to sleep has been shown to delay sleep onset and reduce sleep quality,[5] so has artificial light at night (ALAN) from the outdoor environment.[6,7] ALAN has been increasing several percent yearly over the past decades due to increasing human development and urbanization and may be playing a role in disrupting circadian rhythm.[8,9]

In addition to ALAN, another large component to sleep disruption is noise. In 2011, the WHO published a report on the "burden of disease from environmental noise," estimating almost a million disability-adjusted life-years of sleep lost to noise.[10] Like ALAN, noise may contribute to a delay in sleep latency and has been associated with nocturnal awakenings. As we progress into the later and lighter stages of sleep, external noise stimuli contribute to the possibility of waking earlier.[11] In addition to noise, our increasing urbanization has also disrupted green space and increased air pollution; these additional environmental factors may be linked to sleep disruption. Higher levels of green space have been directly and indirectly associated with improved sleep outcomes. The beneficial associations with green space were seen not only in studies that assessed use of green space (gardening or walking), but were also present in studies that only assessed residential surroundings.[12] It is not clear the exact mechanisms of green space on health, but it is believed that mimicking the natural environment helps improve mental health through the reduction of stress and pain.[13] Last, air pollution has been associated with poorer sleep,[14] potentially due to inflammation and irritation of breathing airways and not limited to individuals with asthma and sleep apnea.[15,16]

The implication of such disruptions extends beyond sleep to other detrimental health outcomes. Mounting evidence of a link between breast cancer and circadian disruption due to night-shift work led the World Health Organization's International Agency for Research on Cancer to classify night-shift work as a probable human carcinogen.[17] We previously reported associations of ALAN with breast cancer and lymphoma in our cohort.[18,19] Air pollution has been associated with a host of adverse health outcomes, including but not limited to cancer risk, cardiovascular disease risk, and impairment of lung function and growth.[20] After adjusting for near-roadway air pollution, noise pollution has also been associated with increased morbidity and mortality. A 2018 meta-analysis found 7% increased risk of diabetes mellitus per 5-decibel (dB) increase in road traffic noise,[21] while a 2021 meta-analysis found no increased risk of death from road traffic noise but did see increased risk from aircraft noise.[22] Finally, higher levels of green space are also associated with improvements in mental health and reduced mortality,[23] with 2 studies reporting up to a 10% reduction in mortality for those living in greener areas.[24,25]

Many studies of environmental sleep disruption examined a single environmental exposure at a time. In this work, we assessed the association of several geospatially derived environmental exposures concurrently on self-reported sleep outcomes in the California Teachers Study (CTS), a large cohort of women residing in California.

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