Breast cancer chemotherapy disrupts sleep

SAN DIEGO, Sept. 1 (UPI) -- Repeated chemotherapy treatments can result in progressively worse and more enduring sleep-wake activity rhythms impairments, U.S. researchers said.

Principal investigator Sonia Ancoli-Israel of the University of California San Diego said the findings were not surprising because sleep disturbances are common in cancer patients and 30 percent to 50 percent report insomnia symptoms.

Although most variables returned to baseline levels in the second and third weeks of the first cycle of chemotherapy, circadian -- 24-hour cycles -- impairments were maintained.

"Results of this study suggest that our biological clocks are affected by chemotherapy," Ancoli-Israel said in a statement.

"Our biological clock, or circadian rhythm help keep our bodies in sync with the environment."

During chemotherapy, the biological clock gets out of sync, especially after the first cycle of treatment, but the clock seems to regulate itself after only one cycle. However, with repeated administration of chemotherapy, it becomes more difficult for the biological clock to readjust," the study said.

The finding is published in the journal Sleep.