Integrative and comparative biologyMar 31, 2021

Nighttime Light and Changed Body Clocks Affect Health and Behavior

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 31, 2026

Abstract

Exposure to light at night (LAN) may disrupt internal biological clocks, impacting multiple physiological and behavioral functions.

Nearly all organisms have internal biological clocks that regulate circadian rhythms in response to light.
LAN exposure has been linked to disruptions in natural light-dark cycles, which can lead to physiological and behavioral changes.
Changes associated with LAN include alterations in immune, endocrine, and metabolic functions.
Behavioral impacts of LAN may affect reproductive, foraging, and migratory activities.
Strategies to lessen the negative effects of LAN on behavior and physiology are discussed.

Simplified

Life on earth has evolved during the past several billion years under relatively bright days and dark nights. Virtually all organisms on the planet display an internal representation of the solar days in the form of circadian rhythms driven by biological clocks. Nearly every aspect of physiology and behavior is mediated by these internal clocks. The widespread adoption of electric lights during the past century has exposed animals, including humans, to significant light at night (LAN) for the first time in our evolutionary history. Importantly, endogenous circadian clocks depend on light for synchronization with the external daily environment. Thus, LAN can derange temporal adaptations. Indeed, disruption of natural light-dark cycles results in several physiological and behavioral changes. In this review, we highlight recent evidence demonstrating how LAN exposure can have serious implications for adaptive physiology and behavior, including immune, endocrine, and metabolic function, as well as reproductive, foraging, and migratory behavior. Lastly, strategies to mitigate the consequences of LAN on behavior and physiology will be considered.

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Nighttime Light and Changed Body Clocks Affect Health and Behavior

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