Sleep duration and cancer risk in women.
OBJECTIVE
The objective was to conduct an analysis of sleep duration and risk of selected site-specific and groups of cancer among a large prospective cohort of California women.


METHODS
The study population was comprised of 101,609 adult females participating in the California Teachers Study. All sites of invasive cancer prospectively diagnosed from baseline (1995-1996) through 2011 were identified through linkage to the California Cancer Registry (n = 12,322). Site-specific analyses focused on the following cancers: breast (n = 5,053), colorectal (n = 983), lung (n = 820), melanoma (n = 749), and endometrial (n = 957). Additionally, we evaluated a group of estrogen-mediated cancers consisting of breast, endometrial, and ovarian cancer (n = 6,458). Sleep duration was based on self-report of average time sleeping in the year prior to baseline. Cox proportional hazard models were used to calculate adjusted hazard ratios and 95 % confidence intervals (HRs, 95 % CI).


RESULTS
Point estimates for all sites and site-specific cancers generally were near or below one for short sleepers (<6 h/night) and above one for long sleepers (10+ h/night); confidence intervals, however, were wide and included unity. Compared to average sleepers (7-9 h/night), long sleepers had an increased risk of the group of estrogen-mediated cancers (HR 1.22, 95 % CI 0.97-1.54, p (trend) = 0.04).


CONCLUSIONS
These analyses suggest that longer sleep may be associated with increased risks of estrogen-mediated cancers. Further studies with more refined measures of sleep duration and quality are warranted.
Cancer Prevention Institute of California, 2001 Center Street, Suite 700, Berkeley, CA, 94704, USA, susan.hurley@cpic.org.
Susan
S
Hurley
Debbie
D
Goldberg
Leslie
L
Bernstein
Peggy
P
Reynolds
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002140:California / Q000453:epidemiology; D005260:Female; D006801:Humans; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D057566:Self Report; D012890:Sleep; D055815:Young Adult