title: Association between sleep duration and cancer risk: a meta-analysis of prospective cohort studies.
abstract: BACKGROUND
  Sleep duration has been shown to play an important role in the development of cancer. However, the results have been inconsistent. A meta-analysis with prospective cohort studies was performed to clarify the association between short or long sleep duration and cancer risk.
  
  
  METHODS
  PubMed and Embase databases were searched for eligible publications. Pooled relative risk (RR) with 95% confidence interval (CI) was calculated using random- or fixed- model.
  
  
  RESULTS
  A total of 10 prospective studies (8392 incident cases and 555678 participants) were included in the meta-analysis. Neither short nor long sleep duration was statistically associated with increased risk of cancer (short sleep duration: RR=1.05, 95%CI=0.90-1.24, p=0.523; long sleep duration: RR=0.92, 95%CI=0.76-1.12, p=0.415). In the subgroup by cancer type, long sleep duration was positively associated with colorectal cancer (RR=1.29, 95%CI=1.09-1.52, p=0.003).
  
  
  CONCLUSIONS
  The present meta-analysis suggested that neither short nor long sleep duration was significantly associated with risk of cancer, although long sleep duration increased risk of with colorectal cancer. Large-scale well-design prospective studies are required to be conducted to further investigate the observed association.
authors.affiliation: Department of Ophthalmology, Jinling Hospital, Nanjing University, Nanjing, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Lu
authors.forename: Nong
authors.initials: N
authors.lastname: Tian
authors.forename: Jie
authors.initials: J
authors.lastname: Yin
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Shi
authors.forename: Zhenping
authors.initials: Z
authors.lastname: Huang
mesh_terms: D015331:Cohort Studies; D006801:Humans; D009369:Neoplasms / Q000453:epidemiology*; D011446:Prospective Studies; D012306:Risk; D012890:Sleep; D013997:Time Factors
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