Individuals with cancer are more likely to experience sleep problems, and poor sleep may increase cancer risk.
With that being said, few studies have investigated the link between sleep duration and risks for cancers other than breast cancer.
A 2016 study set out to determine the link between sleep duration and incidences of 18 specific cancers using data from the NIH-AARP Diet and Health Study. The study included data from 297,185 adults between 50 and 71 years of age. Fifty-eight percent of the cohort were men and 42 percent were women.
Sleep duration was self reported and categorized into the following groups:
- Fewer than five hours
- Between five and six hours
- Between seven and eight hours
- Nine hours or more
Cancers linked with short sleep duration in men
Researchers found a significant increase in stomach cancer risk in men who got between five and six hours of sleep compared to those who slept for between seven and eight hours.
The study also revealed a suggested link between the following cancers and a sleep duration of less than five hours:
- Head and neck cancer
- Myeloma (a cancer of plasma cells)
For men who slept for between five and six hours, a suggested link was made with the following cancers:
- Bladder cancer
- Non-Hodgkin lymphoma
Is short sleep duration beneficial for women?
Interestingly, the study data suggested that women who slept for less than five hours appeared to be less likely to develop breast cancer.
Study data also suggested that women who slept for nine hours or more had a reduced risk for ovarian cancer, but an increased risk for Non-Hodgkin lymphoma.
A few caveats
It's important to note that the link between stomach cancer in men who got between five and six hours of sleep was the only association that reached statistical significance. All other associations were suggested, but did not reach the threshold for statistical significance.
Perhaps most surprising in this research was its suggestion that women who slept for less than five hours were less likely to develop breast cancer.
When it comes to linking breast cancer with sleep duration, previous studies have reported mixed results. A large prospective cohort study published in 2006 concluded that there was no convincing link between sleep duration and the incidence of breast cancer.
A more recent study published in 2015 concluded that there was no association between sleep and overall breast cancer.
So, why did this study find a suggested link between short sleep duration and reduced breast cancer risk? The authors suggest this could be due to their data being obtained from older women — estrogen levels are considered to be a risk factor for breast cancer and short sleep durations may be a symptom of low estrogen in post-menopausal women.
Do other factors or conditions influence risk?
This study adjusted for all cancer risk factors for which it had data. These factors included:
Other studies, however, have linked sleep duration and other health conditions or factors with cancer risk.
One study found a link between long sleep duration (nine hours or more) and colorectal cancer in overweight men who snore. Another found long sleep duration increased colorectal cancer risk in women — but all participants were undergoing hormone replacement therapy.
Thyroid cancer has been linked to women with higher insomnia scores, but no link has been found when it comes to sleep duration.
It's worth nothing that both excessively short sleep durations and excessively long sleep durations may be caused by an underlying health condition, which could influence cancer risk.
There does appear to be a link between sleep health and cancer risk. However, studies report mixed results when it comes to the risk for specific cancers and whether other health conditions or lifestyle factors may influence that risk.
The best thing you can do is recognize the importance of sleep and take steps to improve your sleep if you feel you're not getting enough or if you find that you are regularly sleeping for an excessive amount of time.
Start by talking with your doctor or other health professional about any concerns you may have.
Martin is the creator of Insomnia Land’s free insomnia sleep training. His online course uses CBT techniques to teach participants how to sleep without relying on sleeping pills. More than 4,000 insomniacs have completed his course and 97 percent of graduates say they would recommend it to a friend.