Background: The impact of different sleeping categories on the risk of cancer of the breast has remained debatable. We sought to systematically synthesize the fund of available literature on this relationship from population-based cohort studies using meta-analytic procedures.
Data sources: Studies about napping and cancer of the breasts were identified from databases up to February 2019.
Methods: Identified studies were analyzed for quality using NOS Scores. Effect sizes were visualized using funnel plots. Study heterogeneity was quantified using I2 and visualized using Baujat plots. Publication prejudice was evaluated using Eggers regression model, with visualizations using funnel plots. Analysis were done using R.
Results: Eight cohort studies met the inclusion criteria. Random effects model revealed non-statistically significant evidence of an association between short or long sleep and breast cancer OR=0.90;(95%CI 0.7995-1.0215); p=0.1054 and OR=0.95(0.8886-1.0280);p=0.2234 respectively. There was moderate to high heterogeneity I2(95%CI)=74.4%(48.2%-87.4%) among studies examining short sleep and cancer of the breast, and low to moderate heterogeneity in studies for long sleep and breast cancer I2(95%CI)=3.0%(0.0%-68.6%).
Conclusions: This study found non substantial evidence of associations between sleeping periods and cancer of the breast in women. Studies employing novel sleep measurement methodologies should be carried out to examine the underlying relationship.