Evidence has emerged that different components of sleep, including sleep duration, sleep quality, circadian rhythm, and sleep disorders, can affect cancer risk. That said, studies on this topic are not always consistent or conclusive, which may reflect difficulties in accurately gathering data about sleep over the long-term.
Sleep Duration and Cancer Risk
Studies about the effect of sleep duration on cancer risk have often been conflicting. Differences in results may relate to how sleep data is collected, the types of cancer considered, and how other factors that can influence cancer risk are accounted for.
One large-scale study found that people with short sleep have an increased cancer risk
. Short sleep duration has specifically been associated with a greater risk of colon polyps
that can become cancer. In older adults, some research has tied reduced sleep duration to a higher likelihood of stomach cancer
and found potential correlations with cancers of the thyroid, bladder, head, and neck. These studies, though, are far from definitive. Many types of cancer, including lung cancer
, have not been found to be affected by short sleep in other studies.
Researchers have also looked at long sleep duration, usually defined as sleeping more than nine hours per night, and found potential links to cancer risk. This amount of sleep was found in one study to elevate the risk of colorectal cancer in older adults
, especially those who were overweight or snored frequently. Long sleep duration has been associated with an increase in risk of primary liver cancer
and breast cancer
.