Association between different obesity metrics and risk of inguinal hernia.

Purpose: Obesity is closely associated with a lower risk of inguinal hernia, but the association between different obesity metrics and the risk of inguinal hernia is still unclear.

Methods: In our study, we categorized obesity measurement indicators into three groups based on the difficulty of measurement: (1) indicators easily available, such as body mass index (BMI), waist circumference (WC), hip circumference (HC), and waist-to-hip ratio (WHR); (2) indicators accessible with moderate difficulty, such as body fat percentage and body fat mass; (3) indicators difficultly accessible, such as the volume of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). Mendelian randomization (MR) analysis was used to investigate the causal relationship between various adiposity measures and the risk of inguinal hernia in both European ancestry and East Asians.

Results: We identified a total of 17,096 patients with inguinal hernia in the FinnGen cohort and 1664 cases in the Japan Biobank cohort. For European ancestry, MR analysis reported a significant causal association between one standard deviation increase of BMI, WC, HC, body fat percentage, and body fat mass and the lower risk of inguinal hernia, rather than WHR, VAT, and SAT. After the adjustment of BMI, increased WC is still causally associated with a lower risk of inguinal hernia (OR: 0.52; 95% CI: 0.33-0.80; P < 0.01). Among East Asians, only body fat mass is causally associated with a reduced risk of inguinal hernia, rather than BMI, WC, and HC.

Conclusion: Obesity is causally associated with a relatively lower risk of inguinal hernia. The association between different obesity measures and the risk of inguinal hernia has ethnic specificity. These findings help us deepen our understanding of the intrinsic causal relationship between fat distribution and the risk of inguinal hernias at the genetic level.