Russart, K. L. G., & Nelson, R. J. (2018). Light at night as an environmental endocrine disruptor. Physiology & behavior. https://doi.org/10.1016/j.physbeh.2017.08.029
Russart KLG, Nelson RJ. Light at night as an environmental endocrine disruptor. Physiology & behavior. 2018. doi:10.1016/j.physbeh.2017.08.029
Russart, Kathryn L. G., and Randy J. Nelson. "Light at night as an environmental endocrine disruptor." Physiology & behavior, 2018.
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RRM Academy Synopsis
Light at night acts as an endocrine disruptor, a review concludes
Artificial light at night acts as an endocrine disruptor in humans and wildlife, a 2018 review concludes. The review draws on human studies, rodent experiments and wildlife research. The authors link light at night to suppressed melatonin, weight gain, breast cancer risk and reproductive dysfunction.
Key Findings
A global population-level study the review cites found light at night explained 70% of variation in overweight and obesity prevalence, controlling for other lifestyle factors such as food consumption.
Mice exposed to dim light at night for two weeks reduced energy expenditure and increased body mass, despite caloric intake equivalent to mice kept in dark nights.
Meta-analyses of epidemiological studies of women chronically exposed to light at night found an average increase in breast cancer risk of about 50%.
The authors report a link between circadian dysregulation and reproductive dysfunction and reduced fertility in humans, and describe clock gene activity in the ovary throughout follicle development.
Blackbirds exposed to very low levels of light at night left the photorefractory period almost a month sooner than blackbirds on dark nights.
Interpretation
The paper is a narrative review with no described search method. Most human evidence in the review is observational, drawn from shift workers and country-level comparisons, which show association. Most of the basic science uses nocturnal rodents, which the authors note allow the effects of circadian disruption to be isolated from sleep changes. Most animal cancer studies shifted light cycles, which confounds the effect of light itself, the authors note. One colorectal cancer finding may reflect short sleep, they add. Studies that directly test light and reproductive fitness are lacking, the authors state. They reason from clock gene and melatonin biology that light is likely to harm reproduction.
RRM Context
Restorative reproductive medicine seeks the underlying causes of poor ovulation. The review describes clock activity throughout the female hormone axis from brain to ovary. Melatonin in the fluid around the egg protects it from oxidative stress, the authors report. Wildlife studies in the review describe hormone changes in males and females.
Our editorial summary of this paper, not the article's abstract.
Abstract
Environmental endocrine disruptors (EEDs) are often consequences of human activity; however, the effects of EEDs are not limited to humans. A primary focus over the past ∼30years has been on chemical EEDs, but the repercussions of non-chemical EEDs, such as artificial light at night (LAN), are of increasing interest. The sensitivity of the circadian system to light and the influence of circadian organization on overall physiology and behavior make the system a target for disruption with widespread effects. Indeed, there is increasing evidence for a role of LAN in human health, including disruption of circadian regulation and melatonin signaling, metabolic dysregulation, cancer risk, and disruption of other hormonally-driven systems. These effects are not limited to humans; domesticated animals as well as wildlife are also exposed to LAN, and at risk for disrupted circadian rhythms. Here, we review data that support the role of LAN as an endocrine disruptor in humans to be considered in treatments and lifestyle suggestions. We also present the effects of LAN in other animals, and discuss the potential for ecosystem-wide effects of artificial LAN. This can inform decisions in agricultural practices and urban lighting decisions to avoid unintended outcomes.
