Pre-diagnostic Sleep Duration and Sleep Quality in Relation to Subsequent Cancer Survival

Authors: Phipps, A.I. et. al.

Source: J Clin Sleep Med 2016;12(4):495-503.

www.ncbi.nlm.nih.gov/pubmed/26612513

Several studies have found connections between poor sleep quality and the risks for multiple types of cancer. This group evaluated the relationship between sleep and breast cancer.

The Women’s Health Initiative (WHI) is an ongoing study of postmenopausal women, assessing their health outcomes over time. Over 20,000 WHI participants contributed data to this project. They were breast cancer-free and had provided information about their sleep habits at the time of study enrollment.

Most participants reported sleeping 7-8 hours per night. Among the women who developed breast cancer, those who slept for less than 7 hours a night and women who snored had poorer breast cancer-specific survival. When sleep duration and snoring were combined, the results were statistically significant: women who slept less than 6 hours per night and snored frequently (at least 5 nights per week) had worse breast cancer-specific survival.

There are many explanations for the findings. Insufficient sleep is associated with enhanced production of pro-inflammatory cellular substances. Animal models show that poor sleep results in increased tumor invasiveness and accelerated tumor growth. It is known that progesterone levels are lower in individuals who snore, and these low levels may reflect an adverse environment for breast tissue.

On the other hand, co-morbidities (other illnesses), stress and socioeconomic and living situations may explain the subjects’ sleep habits and more strongly affect their breast cancer outcomes. Sleep habits may just be signs of more influential factors at work.

This study contributes to a small number of investigations between sleep and breast cancer and raises questions about the effect of this aspect of lifestyle upon breast cancer outcomes.