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

SIMPLE SUMMARY: There is also growing evidence for metabolic syndrome as a risk factor for BC. However, no studies have yet looked at how the risk of developing breast cancer varies with changes in metabolic syndrome status. It is important to identify the risk of BC among women who develop or recover from metabolic syndrome in disease prevention. Therefore, this study aimed to investigate the association between changes in metabolic syndrome and subsequent breast cancer occurrence. As a result, the risk of breast cancer differed significantly according to the changes of metabolic syndrome status. Individuals who improved from metabolic syndrome had the same risk of breast cancer as those who were sustained non-metabolic syndrome. Thus, efforts to improve metabolic syndrome may provide an added benefit of a reduced risk of breast cancer. ABSTRACT: Objective: 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. Research Design and Methods: 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. Results: 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. Conclusions: 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.