Too Much Sleep May Up Colon Cancer Risk

Long sleep duration is associated with an increased risk of colorectal cancer, especially among people who snore and are overweight, researchers reported.

In analysis of two long-running prospective observational cohorts, people who reported sleeping at least 9 hours a night were more likely to develop the disease than those who slept an average of 7 hours, according to Xuehong Zhang, MD, ScD, of Harvard Medical School, and colleagues.

But the association was restricted to people who either snored regularly or were overweight, Zhang and colleagues reported in the May issue of Sleep.

There has been little study of potential links between sleep and cancer incidence, although there is some evidence that hypoxemia might play a role, the researchers noted.

The study "adds to the very limited literature regarding the relationship between sleep duration and/or sleep quality and colorectal cancer risk," Zhang said in a statement.

And the "novel observation" that regular snorers who sleep for long periods appear to have an increased risk "raises the possibility that sleep apnea and its attendant intermittent hypoxemia may contribute to cancer risk," Zhang said.

The findings are based on analysis of colorectal cancer incidence among 30,121 men ages 41 to 79 in the Health Professionals Follow-up Study, and 76,368 women ages 40 to 73 in the Nurses' Health Study.

In both studies, participants were asked about sleep duration and snoring in 1986 and 1987. In addition, the long-running studies collect data on demographics, lifestyle, and disease.

Over 22 years of follow-up, Zhang and colleagues reported, there were 1,973 incident colorectal cancer cases, including 709 among men and 1,264 among women.

Compared with people who slept 7 hours nightly on average, those who slept 9 or more appeared to be more likely to develop colorectal cancer: For men, the hazard ratio was 1.35 (95% CI 1.00 to 1.82), while for women it was 1.11 (95% CI 0.85 to 1.44).

But when the analysis was stratified by snoring or body mass index greater than 25, the association became stronger, Zhang and colleagues reported. Specifically:

• In long-sleeping men who snored, the hazard ratio for colorectal cancer was 1.80 (95% CI 1.14 to 2.84)
• In long-sleeping women who snored, the hazard ratio was 2.32 (95% CI 1.24 to 4.36)
• In overweight men, the hazard ratio was 1.52 (95% CI 1.04 to 2.21)
• In overweight women, the hazard ratio was 1.37 (95% CI 0.97 to 1.94)

Short sleep duration (≤ 5 h) was not associated with an increased risk of colorectal cancer in the entire sample or in subgroups stratified by snoring or BMI.

Taken together, the findings suggest that longer sleep duration is linked with an increased risk of developing colorectal cancer among people who were overweight or snored regularly.

But the data remain "sparse," Zhang and colleagues concluded, so more research is needed to pin down the association and any possible mechanism.

They cautioned that the analysis has several limitations, including the self-reported nature of the data about snoring and sleep duration. In addition, unmeasured confounding is possible, and the study population was mainly of European extraction, which may limit the applicability of the findings.