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Dautovich, N. D., Schreiber, D. R., Imel, J. L., Tighe, C. A., Shoji, K. D., Cyrus, J., et al. (2019). A systematic review of the amount and timing of light in association with objective and subjective sleep outcomes in community-dwelling adults. Sleep Health, 5(1), 31–48.
Abstract: Light is considered the dominant environmental cue, or zeitgeber, influencing the sleep-wake cycle. Despite recognizing the importance of light for our well-being, less is known about the specific conditions under which light is optimally associated with better sleep. Therefore, a systematic review was conducted to examine the association between the amount and timing of light exposure in relation to sleep outcomes in healthy, community-dwelling adults. A systematic search was conducted of four databases from database inception to June 2016. In total, 45 studies met the review eligibility criteria with generally high study quality excepting for the specification of eligibility criteria and the justification of sample size. The majority of studies involved experimental manipulation of light (n = 32) vs observational designs (n = 13). Broad trends emerged suggesting that (1) bright light (>1000 lux) has positive implications for objectively assessed sleep outcomes compared to dim (<100 lux) and moderate light (100-1000 lux) and (2) bright light (>1000 lux) has positive implications for subjectively assessed sleep outcomes compared to moderate light (100-1000 lux). Effects due to the amount of light are moderated by the timing of light exposure such that, for objectively assessed sleep outcomes, brighter morning and evening light exposure are consistent with a shift in the timing of the sleep period to earlier and later in the day, respectively. For subjectively assessed sleep outcomes, brighter light delivered in the morning was associated with self-reported sleep improvements and brighter evening light exposure was associated with worse self-reported sleep.
Kalousová, L., Xiao, B., & Burgard, S. A. (2019). Material hardship and sleep: results from the Michigan Recession and Recovery Study. Sleep Health, 5(2), 113–127.
Sleep is unequally distributed in the US population. People with low socioeconomic status report worse quality and shorter sleep than people with high socioeconomic status. Past research hypothesized that a potential reason for this link could be exposure to material hardship. This study examines the associations between several material hardships and sleep outcomes.
We use population-representative cross-sectional data (n = 730) from the Michigan Recession and Recovery Study collected in 2013 and examine the associations between 6 indicators of material hardship (employment instability, financial problems, housing instability, food insecurity, forgone medical care, and the total number of material hardships reported) and 3 sleep outcomes (short sleep, sleep problems, and nonrestorative sleep). We build multivariable logistic regression models controlling for respondents’ characteristics and light pollution near their residence.
In unadjusted models, all material hardships were associated with negative sleep outcomes. In adjusted models, forgone medical care was a statistically significant predictor of nonrestorative sleep (average marginal effect 0.16), as was employment instability (average marginal effect 0.12). The probability of sleep problems and nonrestorative sleep increased with a greater number of hardships overall (average marginal effects of .02 and .05, respectively). We found marginally statistically significant positive associations between food insecurity and short sleep and sleep problems.
This study finds that, except when considering foregone medical care, employment instability, and total count of material hardships, associations between material hardship and negative sleep outcomes are not statistically significant after adjusting for a robust set of sociodemographic and health characteristics.