After adjusting for genetic associations with BMI, AAM per-year on BC risk were HR = 0.90 (95%CI:0.83-0.98, p = 0.01) and HR = 0.95 (95%CI:0.86-1.04, p = 0.26) for BRCA1 and BRCA2 carriers, respectively, consistent with a protective effect of later AAM.<h4>Discussion</h4>MR analyses support causal associations between ANM and BC risk in BRCA2, but not BRCA1, and between AAM and BC risk in BRCA1 and BRCA2 PV carriers. This evidence concerns the gene BRCA2 and breast cancer.