The Nurses’ Health Study is one of the largest investigations into risk factors for chronic disease in women. Utilizing questionnaires nurses completed about their health, the Nurses’ Health Study has given rise to many research papers from its extensive data pool In a 2017 study entitled “Sleep and survival among women with breast cancer: 30 years of follow-up within the Nurses’ Health Study,” researchers explored sleep difficulty (or quality of sleep, defined as difficulty falling and/or staying asleep), and sleep duration in women with stage I or II non-metastatic breast cancer in order to better understand how these variables relate to mortality and cancer recurrence.
Researchers divided women into three groups: “short sleepers” - those who slept on average less than or equal to 5-6 hours; “long sleepers” - those who slept 9 hours or more; and those in the middle, divided into 7 hour and 8 hour groups. Researchers found that women with breast cancer who slept at least nine hours had a 37% greater risk for all-cause cancer and a 46% greater risk for breast cancer than those who slept eight hours. No association was found for short sleepers. An increase in sleep duration from pre to post diagnosis compared to no change was associated with a 35% higher risk of all-cause death.
The increased mortality observed among long sleepers corroborates recent meta-analyses demonstrating an association between sleep duration and both all-cause and cardiovascular death in the general population, suggesting that the elevated health risk among long sleepers is not limited to a single organ system or condition, rather it may impair health function globally. However, the association between elevated breast cancer risk specifically and long sleeping is novel.
Surprisingly, short sleep duration was not statistically associated with mortality in this research, although previous studies have shown that both short and long durations of sleep are associated with an increased cancer incidence, while other research has revealed inverse relationships between sleep and cancer occurrence. Researchers in this study did find a statistical significance between short sleep and depression however, where short sleepers (less than 6 hours) reporting depression had a higher breast cancer mortality risk than those who slept 8 and 9 hours[DL1] . This link between depression and death was only noted in the short sleepers.
Researchers hypothesized that the additional hours of sleep might reflect a patient’s psychological response to the cancer diagnosis and/or treatments. For example, fatigue is a common side effect of cancer treatment. While napping seems like a short-term strategy for fatigue, it may disrupt the sleep-wake cycle over time and contribute to insomnia. Poor sleep quality (difficulty falling or staying asleep), frequently seen in up to 70% of non-metastatic breast cancer patients within the first months following diagnosis, may contribute to impaired immune function, obesity and altered melatonin release[DL2] . Women who reported regular sleep difficulties, independent of hours spent sleeping, had a 49% increased risk of all-cause mortality compared to women without such frequent difficulties[DL3] .
Researchers further hypothesized confounding mechanisms that could contribute to over-sleeping including depression, sleep fragmentation, sleep apnea, and fatigue, all circumstances which could lead one to stay in bed longer. Additionally, while not considered statistically significant, researchers did note several qualities and behaviors in the over-sleepers that may have contributed to the recurrence of cancer and overall mortality. The over-sleepers consumed 40-80 more calories per day than 6-8 hour sleepers. They also reported less physical activity, a higher BMI, and consumed more alcohol than the other groups. While each of these qualities and behaviors are risk factors for many diseases, this research suggests the combination with over-sleeping may prove more dangerous than previously understood.
While it’s commonly assumed that if some sleep is good, more is better, this research suggests that long sleep may be a symptom of other underlying metabolic, social and psychological factors influencing women with breast cancer. Bottom line: sleeping 7 or 8 hours without difficulties postures women with breast cancer for a greater chance of survival and lower chance of recurrence.
If your patients are having difficulty staying or falling asleep for any reason, including breast cancer treatment, cortisol and melatonin testing may provide insight and help guide treatment protocols. Labrix’s three-point Melatonin Profile can be added to any saliva test, including the Adrenal Function Profile.