Women with breast cancer who sleep for longer every night, and who report regular sleep difficulties, had higher all-cause and breast cancer mortality, according to a new study.
“Women with breast cancer are likely to report poor sleep quality, in a higher proportion than what is generally reported among the general population and by patients with other cancer sites,” wrote study authors led by Claudia Trudel-Fitzgerald, PhD, of the Harvard T. H. Chan School of Public Health in Boston. Previous work has not thoroughly evaluated the relationship between sleep and survival outcomes.
This study included 3,682 breast cancer patients included in the Nurses’ Health Study who reported their average sleep duration following their diagnosis. Subgroups also reported pre-diagnosis sleep duration (1,949 patients) and post-diagnosis sleep difficulties (1,353 patients). The results were published in the British Journal of Cancer.
On average women were 64.9 years old at diagnosis, and most had early-stage cancer. There were 976 deaths during the study, including 412 due to breast cancer and 564 non–breast cancer deaths.
Women who slept 9 hours or more per night had a higher risk of all-cause mortality, with a hazard ratio (HR) of 1.45 (95% CI, 1.16–1.80), compared with a reference group of women who slept 8 hours per night. Those who slept 7 or 6 hours or less did not have a significantly different risk compared with those who slept 8 hours.
This was also true for breast cancer deaths; in the 9-hours/night group, the HR was 1.49 (95% CI, 1.05–2.10). Specifically for non–breast cancer deaths, the HR was 1.40 (95% CI, 1.05–1.87). In both cases again, those who slept less did not have significantly different risk.
A change in sleep duration from before to after diagnosis of breast cancer was also associated with higher risk. Compared with those whose sleep duration did not change, those whose sleep duration increased had an HR for all-cause mortality of 1.41 (95% CI, 1.10–1.81). Those whose duration decreased had an HR of 1.29 (95% CI, 0.99–1.68). The relationship was significant for non–breast cancer deaths, but not for breast cancer–specific deaths.
On a multivariate analysis, women who reported “regular” difficulties initiating or maintaining sleep had an HR for all-cause mortality of 1.48 (95% CI, 1.01–2.16) compared with those who rarely or never had such difficulties.
The authors noted that the elevated risk for longer sleepers is consistent with other research on all-cause and cardiovascular mortality in the general population, but the elevated breast cancer–specific mortality is a novel finding.
“If these results are replicated in future work, it will be important to evaluate breast cancer patients for long and changing sleep duration, in addition to sleep difficulties in the clinical setting, to identify patients who may be at risk for poor outcomes,” they concluded.