Circadian Rhythm

Research summary

• Shift work is the best human model for studying real-world circadian disruption, and the evidence here is unusually consistent: two independent dose-response meta-analyses find shift work increases cardiovascular disease morbidity and mortality, and a more recent meta-analysis of night shift work specifically confirms elevated cardiovascular risk indicators.
• The cancer literature is similarly well-replicated: a classic 2013 meta-analysis and three more recent, independent meta-analyses (through 2024) all find night-shift work is associated with elevated breast cancer risk, with a dose-response relationship in the most recent analysis, and shift work is separately linked to elevated skin cancer risk.
• A dedicated meta-analysis also found shift work during pregnancy is associated with worse maternal and infant health outcomes.
• Because shift work is the dominant human circadian-disruption model in this literature, the strength of evidence here says more about occupational circadian misalignment specifically than about milder day-to-day circadian variation in the general population.