Shift work and circadian misalignment

Shift work is any schedule that pushes your working hours outside the usual 7am-to-6pm window, including fixed nights and rotating shifts. It chronically misaligns your behavior cycles (sleep, eating, activity) with your internal ~24-hour body clock, run by a brain region called the suprachiasmatic nucleus (SCN). Light at night suppresses melatonin, flips the cortisol rhythm, and pushes meals into biologically night-time hours. That creates internal desynchrony: your central clock and your organ clocks fall out of step. A controlled lab study (Scheer et al., PNAS 2009) showed something striking. Even a few days of misalignment raised blood pressure, raised post-meal glucose and insulin, and lowered leptin in healthy adults. Those changes look like early prediabetes and hypertension if sustained. In the UK Biobank (Yang et al., JAHA 2022, about 36,900 people), the picture held. People with high blood pressure who usually or always worked nights had a 16% higher risk of having several cardiometabolic diseases at once (diabetes, coronary disease, or stroke), versus day workers. The IARC classified night-shift work as a 'probable human carcinogen' (Group 2A) in 2007, reaffirmed in 2019. It cited limited human signals for breast, prostate, and colorectal cancer, plus animal evidence. The cancer link in humans is still associational. But the metabolic and heart burden from circadian disruption is well-supported. And it is directly relevant to accelerated aging.

Last reviewed: June 22, 2026

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