Sex differences in the association between fatty liver and type 2 diabetes incidence in non-obese Japanese: A retrospective cohort study

Aims/introduction: Asians develop type 2 diabetes at a lower body mass index (BMI) compared with other races, which is partly because of Asian-specific fat depots. Sex plays a role in fat deposition, regardless of race. This retrospective cohort study aimed to investigate the association among fatty liver, sex and type 2 diabetes in non-obese Japanese.

Materials and methods: The participants in this study (13,596 men and 6,037 women) were aged 30-64 years, and had undergone health checkups between 2013 and 2015, in Aichi, Japan. Baseline BMI was categorized as follows: <18.5, 18.5-19.9, 20-22.9, 23-24.9, 25-27.4 and ≥27.5 kg/m² . Fatty liver was diagnosed by abdominal ultrasonography. The joint effect of BMI and fatty liver on the incidence of type 2 diabetes was assessed, stratified by sex.

Results: During follow up, 738 men and 138 women developed type 2 diabetes. Compared with the BMI of 20-22.9 kg/m² without fatty liver group, the BMI of 20-22.9 kg/m² with fatty liver was associated with a higher risk of type 2 diabetes in men, but not in women. Furthermore, men with a BMI of 23-24.9 and 25-27.4 kg/m² without fatty liver had no significant type 2 diabetes risk, whereas women with a BMI of 23-24.9 and 25-27.4 kg/m² , regardless of fatty liver, had an increased risk.

Conclusions: These results suggest the association between fatty liver and type 2 diabetes in non-obese Asians is different by sex; fatty liver increases diabetes risk among male, not female, non-obese Asians.