Women who regularly work night shifts or frequently travel across time zones may face a higher risk of developing aggressive breast cancer, according to a new study by researchers at Texas A&M University.
The research suggests that disrupting the body’s internal clock, also known as the circadian rhythm, can change breast tissue structure and weaken the immune system. These changes may allow cancer to develop earlier and spread more easily.
“Cancer keeps time,” said Dr. Tapasree Roy Sarkar, co-director of the Center for Statistical Bioinformatics at Texas A&M University. “When your internal clock is disrupted, cancer takes advantage. But our findings also point toward a possible way to fight back.”
Circadian rhythms control far more than sleep. They help regulate hormone release, tissue repair, and how the immune system detects and responds to threats. When this rhythm is disturbed, the body’s natural defenses can break down.
To study the effects, researchers used two groups of genetically engineered models that are prone to developing aggressive breast cancer. One group followed a normal day-and-night light cycle, while the other was exposed to a disrupted light schedule designed to interfere with their internal clocks.
The results, published in the journal Oncogene, showed a clear difference. Models with normal sleep cycles typically developed cancer at around 22 weeks. Those with disrupted circadian rhythms began showing cancer signs much earlier, at about 18 weeks.
The tumors in the circadian-disrupted group were also more aggressive and more likely to spread to the lungs, which is linked to poorer outcomes in breast cancer patients.
Researchers also observed that circadian disruption weakened immune defenses. This created an environment where cancer cells could grow and spread more easily.
“It wasn’t just that the tumors grew faster,” Sarkar explained. “The immune system was actively suppressed, giving cancer cells better conditions to survive.”
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The impact went beyond tumor growth. Long-term disruption of the internal clock also altered healthy breast tissue, making it more vulnerable to cancer development. The researchers found noticeable changes in the structure of mammary glands, the milk-producing tissue of the breast.
