Association Between Body Mass Index and Myopia: Results from NHANES and Mendelian Randomization.

Purpose: Previous studies have shown a conflicting association between body mass index and myopia. This study aimed to analyze the possible association between Body Mass Index (BMI) and myopia in the observational design and genetic evidence.Methods: In the observational investigation, 5,710 participants (12-25 years) from the 2001-2006 National Health and Nutrition Examination Survey (NHANES) were included. Weighted logistic regression models, restricted cubic spline (RCS) and stratified analysis were conducted in the NHANES. A two-sample Mendelian Randomization (MR) study using Genome-Wide Association Studies (GWAS) summary statistics and GWAS catalog was performed. The inverse-variance weighted (IVW) method was used as the main analysis method, and the sensitivity analysis was performed to detect pleiotropy and heterogeneity bias.Results: In the fully adjusted model, individuals with obesity had a higher risk of myopia [OR = 1.253, 95% CI= (1.049, 1.496), p = 0.014] and mild and moderate myopia [OR = 1.305, 95% CI= (1.094, 1.558), p = 0.004]. BMI was correlated with refractive spherical equivalent and showed a linear relationship (P for nonlinearity = 0.468, p = 0.002,β=-0.016). In males, obesity had an association with myopia, while there was no statistical significance in females. In the subgroup with an education level of < 9th Grade, obesity and myopia exhibited consistent results. Two-sample MR showed that obesity had no statistically significant with myopia and refractive error.Conclusions: This study suggests that the associations between BMI and the risk of myopia differ based on gender and education levels in an observational study, while there are no associations in genetic evidence.