Frumkin’s commentary links the built environment to health risks associated with SARS-CoV-2 and other diseases (Frumkin 2021). He focuses on risk factors such as crowding, poverty and racism, poor air circulation, and air pollution. However, light as an important codeterminant of health resilience is somewhat left out.
Millions of years of evolution have resulted in daylight becoming a key environmental time cue for regulating our internal circadian timing system (CTS) (Aschoff 1951). The CTS—a clockwork system present in every cell of the body—organizes countless fundamental processes into circadian rhythms of rest and excess (Foster and Wulff 2005; Pittendrigh 1960). Via facets of hormone regulation, cell growth and repair, metabolism, sleep, and immune system functions, the CTS contributes substantially to fighting off disease. Inappropriate or insufficient light exposure can result in transient periods of circadian rhythm misalignment and has been associated with psychiatric disorders, obesity, diabetes, cardiovascular disease, and even cancer in the long term (IARC 2019).
During the COVID-19 pandemic, we raised health questions about reduced daylight and the CTS in lockdown settings (Erren and Lewis 2020; Erren et al. 2020). Moreover, it has been hypothesized that sunlight-associated vitamin D levels could bolster immune responses when fighting infectious diseases and that daylight-associated immune seasonality in humans may contribute to COVID-19 seasonality (Kronfeld-Schor et al. 2021).
The breadth of physiology co-governed by the light-stimulated CTS and the implications of CTS disturbance are underappreciated (Lewis et al. 2018). Frumkin’s brief mentions of the light environment (“building codes to assure adequate light” and “health concerns of [working from home] include poor lighting”) deserve general elaboration. More specifically, building codes may need revision based on research into the “spectral diet” of humans (Webler et al. 2019). This change in codes could allow provision of truly adequate light instead of the often-confusing mix of natural and artificial light input to the CTS in today’s built environments. Poor light environments may contribute to Frumkin’s description of “worse baseline health” based on inequality.
Ultimately, controlling effects of all the risk factors above could benefit from fostering a resilience-lending light environment. In practice, we could aim for maximized exposures to sunlight (Bellia and Fragliasso 2021)—complemented physiologically by artificial light—during days and reduce light pollution during nights (Kerenyi et al. 1990).
Overall, and in line with Frumkin’s closing words, urbanization targeting optimized light for the CTS may “make healthier, more sustainable, and more resilient places than ever before.”
Refers to https://doi.org/10.1289/EHP8888
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