Changes in Metabolic Syndrome Status and Breast Cancer Risk: A Nationwide Cohort Study

To our knowledge, no studies have yet looked at how the risk of developing breast cancer (BC) varies with changes in metabolic syndrome (MetS) status. This study aimed to investigate the association between changes in MetS and subsequent BC occurrence.

We enrolled 930,055 postmenopausal women aged 40-74 years who participated in a biennial National Health Screening Program in 2009-2010 and 2011-2012. Participants were categorized into four groups according to change in MetS status during the two-year interval screening: sustained non-MetS, transition to MetS, transition to non-MetS, and sustained MetS. We calculated multivariable-adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for BC incidence using the Cox proportional hazards models.

At baseline, MetS was associated with a significantly increased risk of BC (aHR 1.11, 95% CI 1.06-1.17) and so were all of its components. The risk of BC increased as the number of the components increased (aHR 1.46, 95% CI 1.26-1.61 for women with all five components). Compared to the sustained non-MetS group, the aHR (95% CI) for BC was 1.11 (1.04-1.19) in the transition to MetS group, 1.05 (0.96-1.14) in the transition to non-MetS group, and 1.18 (1.12-1.25) in the sustained MetS group.

Significantly increased BC risk was observed in the sustained MetS and transition to MetS groups. These findings are clinically meaningful in that efforts to recover from MetS may lead to reduced risk of BC.