We aimed to examine the association between education level and breast cancer incidence by a meta-analysis of cohort studies.
Relevant studies were identified by searching PubMed, Web of Science, and Scopus databases on June 10, 2018. Reference lists from the obtained articles were also reviewed. We included cohort studies reporting relative risks with 95% CIs for the association between education level and breast cancer incidence. Either a fixed- or random-effects model was used to calculate the pooled risk estimates.
We identified 18 cohort studies with more than 10 million women. Compared with women with a lower education level, women with a higher education level had a significantly higher risk of developing breast cancer (pooled relative risk 1.22 [95% CI, 1.14-1.30]). The results did not differ by study area or reference group. The association remained in studies that adjusted for age at first birth and parity, but was attenuated and no longer significant when the analysis was restricted to studies that adjusted for alcohol use, to studies that adjusted for age at menopause, or to studies that adjusted for hormone therapy.
A higher education level may be associated with an increased risk of developing breast cancer, in which alcohol use, age at menopause, and hormone therapy may, at least partially, play a mediating role.