Irregular sleep routines, particularly among women working night shifts or travelling frequently across time zones, may substantially elevate the risk of developing aggressive breast cancer, researchers have reported.
Evidence indicates that disturbances in circadian rhythms can damage breast tissue and weaken immune responses, allowing cancer cells to thrive.
Circadian rhythms, known as the body’s natural 24-hour timing system, regulate not only sleep but also hormone secretion, tissue repair, and immune monitoring. Once this system becomes misaligned, the body’s defence mechanisms struggle to function effectively.
“Cancer keeps time. If your internal clock is disrupted, cancer takes advantage — but now we’ve found a new way to fight back,” said Dr Tapasree Roy Sarkar, Co-Director of the Centre for Statistical Bioinformatics at Texas A&M University College of Arts and Sciences.
To explore these effects, scientists examined two groups of genetically engineered models prone to aggressive breast cancer. One group followed a standard day-night cycle, whereas the other experienced an altered light schedule designed to disrupt internal timing.
“The circadian rhythm orchestrates how our tissues function, and how our immune system recognises danger,” Dr Tapasree Roy Sarkar said. “When that rhythm is disrupted, the consequences can be seriously dangerous.”
Earlier Cancer Onset Seen in Disrupted Cycles
Results published in the journal Oncogene revealed a striking contrast. Models with stable circadian rhythms developed cancer at around 22 weeks, while those with disrupted cycles showed signs of cancer much earlier, close to the 18-week mark.
Notably, tumours in the circadian-disrupted group proved far more aggressive. These cancers showed a higher tendency to spread to the lungs, a factor strongly associated with poorer outcomes in breast cancer patients.
“It wasn’t just that tumours grew faster,” Dr Sarkar said. “The immune system was actively restrained, creating more favourable conditions for cancer cells to survive and spread.”
Beyond tumour behaviour, prolonged circadian disruption also altered normal breast tissue. Structural changes in the mammary glands were observed, increasing susceptibility to cancer development over time.
Dr Sarkar said, “We observed clear changes in the morphology of the mammary glands, the milk-producing tissue of the breast.”
Overall, the findings reinforce growing concerns about long-term sleep disruption and its broader health consequences. They also highlight circadian regulation as a potential focus for future cancer prevention and treatment strategies.
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