European journal of epidemiologyDec 15, 2018

Widespread Disruption of the Body’s Clock May Lead to Cancer

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Apr 5, 2026

Abstract

Circadian disruption is implicated in cancer causation and may be more widespread than previously considered.

Circadian disruption was classified as probably carcinogenic by the International Agency for Research on Cancer in 2007.
Epidemiological studies have produced inconclusive results regarding the causal links between circadian disruption and cancer.
Focusing solely on shift work, light exposure at night, sleep, and melatonin may overlook the complexity of circadian disruption.
Ubiquitous circadian disruption is suggested as a potentially unexplored epidemiological factor in cancer risk.
Previous studies may have failed to detect cancer risks due to misclassification of exposure to circadian disruption.

Simplified

Circadian disruption (CD) was implicated in chains of cancer causation when the International Agency for Research on Cancer classified shift-work involving circadian disruption as probably carcinogenic in 2007. In the following decade, epidemiological studies into causal concepts associated with circadian disruption were inconclusive. Unappreciated complexity with an exclusive focus on shift-work, light-at-night, sleep, and melatonin in regard to circadian disruption may be accountable. With compelling non-epidemiological evidence, we posit that ubiquitous circadian disruption causes cancer and, moreover, that this is unexplored epidemiologically. This hypothesis offers a novel explanation why numerous studies in shift-workers evince inconsistent results: If circadian disruption is a ubiquitous causal phenomenon, confining assessments to the workplace, ignoring circadian disruption at play, and potential misclassification of 'who' is 'when' and 'how much' exposed to circadian disruption may disallow detecting the existence and magnitude of cancer risks. The rationale herein provides plausible explanations for previous observations and makes falsifiable predictions.

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Widespread Disruption of the Body’s Clock May Lead to Cancer

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