Association Between Fatty Liver Index and Risk of Breast Cancer: A Nationwide Population-Based Study.

Although nonalcoholic fatty liver disease (NAFLD) has been linked to breast cancer risk, the actual relationship remains unclear. Fatty liver index (FLI) is a noninvasive method for predicting NAFLD. We aimed to assess the association between FLI, a predictor of NAFLD, and breast cancer risk.Using the Korean National Health Insurance Corporation data, we reviewed 7,046,153 women who underwent biennial evaluations between 2009 and 2010. FLI was calculated using body mass index, waist circumference, triglyceride level, and gamma-glutamyl transferase level. FLI < 30 ruled out hepatic steatosis, while FLI ≥ 60 indicated NAFLD. Cox regression models were used for analysis.Among the subjects, 51.8% (n = 3,606,079) were premenopausal women. In the premenopausal and postmenopausal groups, 32,145 (0.89%) and 28,103 (0.82%) women developed breast cancer, respectively (median follow-up, 7.02 years; interquartile range, 6.39-7.39 years). Mean FLI and standard deviation were lower in premenopausal women (11.24 ± 14.72 vs. 23.88 ± 19.54, P < .0001). Three groups were formed according to FLI: < 30 (n = 5,693,730, 80.81%), 30-60 (n = 1,031,025, 14.63%), and ≥ 60 (n = 321,398, 4.56%). FLIs of 30-60 and ≥ 60 were significantly associated with increased breast cancer risk in postmenopausal women (hazard ratio, 1.07; 95% confidence interval, 1.04-1.11; and hazard ratio, 1.11; 95% confidence interval, 1.05-1.17, respectively). No association was found in premenopausal women.High FLI, an indicator of NAFLD, could predict breast cancer in postmenopausal women.