MINNEAPOLIS — Depression is what keeps breast cancer survivors up at night, according to data from a study of more than 2,000 women.
“Depression is consistently the strongest predictor of insomnia in these breast cancer survivors,” Wayne A. Bardwell, Ph.D., said at the annual meeting of the Associated Professional Sleep Societies.
In general, women who have survived breast cancer report a high rate of insomnia, compared with the general population, he said.
To determine the relative importance of a range of risk factors for insomnia in breast cancer survivors, Dr. Bardwell and his colleagues at the University of California, San Diego, surveyed 2,101 women at four time points: at baseline, at 1 year, at either 2 or 3 years, and at 4 years after they had completed their cancer treatments. The study was supported by several organizations including Susan B. Komen for the Cure (formerly the Susan G. Komen Foundation), the Lance Armstrong Foundation, and the Walton Family Foundation.
The women were classified as having persistent insomnia, remittent insomnia, or normal sleep based on their responses on the Women's Health Initiative Insomnia Rating Scale (WHIIRS).
Overall, 14% of the women met the criteria for persistent insomnia (scores of 9 or higher on the WHIIRS at all time points). Another 45% fell into a pattern of mixed or remitting insomnia (scores of 9 or higher at some, but not all, time points), and 40% were consistently normal sleepers (scores lower than 9 at all time points).
After controlling for multiple variables, including cancer data, personal characteristics, health behaviors (such as diet and exercise), physical health, and emotional health, only depression and night sweats were significantly associated with chronic insomnia.
All the women in the study had early-stage breast cancer (ranging from stage I to stage IIIA), with no metastases. “Most of the women were stage II and they averaged 2 years since their diagnoses,” Dr. Bardwell noted. About 40% of the women had been initially treated with surgery.
Cancer-specific variables were unimportant in predicting whether the women experienced persistent or remittent insomnia, the researchers concluded.
The findings supported Dr. Bardwell's recent study of baseline insomnia (rather than chronic insomnia) in the same group of women, which also showed that only depressive and vasomotor symptoms in the form of night sweats were significantly associated with insomnia immediately after the completion of treatment for early-stage breast cancer (Psychooncology 2007 Apr. 11 [Epub doi:10.1002/pon.1192]).
Dr. Bardwell's study did not address how or whether the women were treated for their insomnia and depression. The use of low-dose sedating antidepressants is becoming more common as a way to manage chronic insomnia, but more dose-related studies of safety and effectiveness are needed in a range of patient populations.