NEW DELHI: (IANS) Women working on the night shift or frequently flying across time zones, where they experience an irregular sleep schedule, may increase their risk of aggressive breast cancer, according to a study.

The team from the Texas A&M University College of Arts and Sciences explained that circadian disruptions change the structure of mammary glands and weaken the immune system's defenses, all the while pointing toward a new way to counteract these effects.

"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 Center for Statistical Bioinformatics at Texas A&M University College of Arts and Sciences.

Circadian rhythms -- our internal 24-hour clock -- do far more than regulate sleep. They help coordinate hormone release, tissue repair, and the immune system's surveillance.

When disrupted, the body's natural defenses begin to falter.

"The circadian rhythm orchestrates how our tissues function, and how our immune system recognizes danger," Sarkar said. "When that rhythm is disrupted, the consequences can be seriously dangerous."

To investigate these effects, the researchers used two groups of genetically engineered models that develop aggressive breast cancer.

One group lived on a normal day-night schedule, while the other lived on a disrupted light cycle that threw off their internal clocks.

The findings, published in the journal Oncogene, showed that typical models develop cancer around the 22-week marker. The circadian-disrupted group, however, showed signs of cancer much earlier -- at almost 18 weeks.

Tumours in circadian-disrupted models were also far more aggressive and far more likely to spread to the lungs, a key indicator of poor outcomes in breast cancer patients.

At the same time, disruption of the models' internal clock suppressed immune defenses, creating a more hospitable environment for cancer growth.

"It wasn't just that tumours grew faster," Sarkar said. "The immune system was actively restrained, creating more favourable conditions for cancer cells to survive and spread."

But the effects weren't just limited to the tumours themselves. The researchers also found that long-term circadian disruption changed the makeup of healthy breast tissue, making it more vulnerable to cancer.

"We observed clear changes in the morphology of the mammary glands, the milk-producing tissue of the breast," Sarkar said.