LB44
Sleep duration and breast cancer risk: a meta-analysis
Xiaosi Wang, Benjamin Cairns, Ruth Travis
University of Oxford, UK
Background
It is hypothesised that sleep duration affects the production of melatonin and
subsequently influences cancer risk. The relationship between sleep
duration and risk of breast cancer has been investigated recently but findings
from epidemiological studies have been inconsistent and have not been
summarised quantitatively. We aimed to conduct a meta-analysis of observational
studies of the association between sleep duration and breast cancer.
Method
Relevant publications were identified from reviews and computer-aided searches
using PubMed, with keywords sleep duration, breast cancer, survival rate,
mortality, morbidity, incidence and risk, up to July 23rd,
2009. Relative risk estimates and 95% confidence intervals were extracted
for the comparison between the highest exposure group, women who slept ≥
9 hours, and the reference group that comprised women who had a moderate sleep
duration (7 or 8 hours). Summary relative risks were estimated by
calculating the average of the log relative risks, weighted by the inverse
variances of the log relative risks.
Results
Five studies, four with prospective data and one case-control study, were
identified on the risk of breast cancer in relation to sleep duration.
The published data include 9,166 women with incident invasive breast cancer and
147,344 women without breast cancer. When results from these studies were
combined, the aggregate relative risk was 0.96 (95% confidence interval
0.86-1.07) for women with the longest sleep duration compared to those in the
reference group with a shorter sleep duration. When analysis was
restricted to prospective data, the aggregate relative risk was 0.89 (95% CI
0.78-1.01). There was no evidence for significant heterogeneity in this
association by menopausal status.
Conclusion
Meta-analysis of the published epidemiological data provides no strong evidence
for a relationship between sleep duration and risk of breast cancer.
