Recent evidence shows that sleep and cancer risks may be linked.Sleep duration, as well as sleep disturbances or conditions, have been associated with increased risks of acquiring cancer.
Sleep Duration And Cancer
According to an article published in the Journal of Cancer Epidemiology, evidence suggests that short sleep is linked to augmented risk of breast cancer. A study in which 927 breast cancer patients were evaluated showed a modest association between short sleep duration and higher tumor grade in post-menopausal patients. Additionally, multiple studies have also reported an association between short sleep and higher cancer risk.
The Asian Pacific Journal of Cancer Prevention also published a research article whose goal was to assess the association between sleep duration and cancer risk. Researchers performed a thorough search utilizing data published in PubMed, Embase, and Web of Science. They combined hazard ratios from the individual studies using meta-analysis approaches. This meta-analysis suggested an inverse association between long sleep duration and hormone-related cancers (such as breast cancer). On the other side, this meta-analysis suggested a positive link between long sleep and colorectal cancer.
Sleep Disturbances And Cancer
As we mentioned, not only sleep duration seems to be associated with increased cancer risk. As a study, the Million Women Study, published in the British Journal of Cancer (2012) showed , sleep disturbances can have an effect on cancer risk. This study estimated the relative risks of getting breast cancer and other types of invasive cancer, related to the frequency of daytime napping. The result of this study in which 795238 women aged 50-64 were recruited and followed-up during an average of 7.4 years, showed that, overall, frequent daytime napping was associated with a small increase in cancer risk during the first four years of follow-up. Consequently, napping can be a marker of pre-clinical disease in some women.
Another sleep condition that has been linked to cancer is sleep apnea. In 2008, Abrams et al. published that sleep apnea-hypopnea syndrome (SAHS), which has intermittent hypoxia as its primary consequence, could be associated with increased risk of cancer or poorer prognosis in pre-existing cases. He concluded that considering the relationships reported between tissue hypoxia (deficiency of oxygen that reaches the tissues) and cancer.
Two subsequent large studies, as well as posterior smaller ones, confirmed that the severity of nocturnal hypoxia in patients suffering from SAHS was associated with higher risks of cancer and mortality.
Too many studies suggest that sleep deprivation and sleep disturbances increase the risk of cancer. However, some results are not significant yet. Therefore, large-scale, properly-designed prospective studies should be conducted to confirm or disprove the observed associations. Nevertheless, considering that sleep deprivation has been proved to affect negatively mental and physical health, it is always advisable to maintain healthy sleeping habits, sleeping the necessary and recommended hours.
Note: The National Sleep Foundation (Arlington, Virginia), along with a multidisciplinary panel of experts updated its recommendations for adequate sleep durations, which vary depending on the age.
As published in the “Sleep Health: The Journal of the National Sleep Foundation”, it recommends between 7 to 9 hours of sleep for adults between 26-64.