Association between body mass index and myopia in the United States population in the National Health and Nutrition Examination Surveys 1999 to 2008: a cross-sectional study

Background This study investigated the association between body mass index (BMI) and myopia in the United States.Methods This cross-sectional study included 8,000 participants from the 1999 to 2008 National Health and Nutrition Examination Survey (NHANES). BMI was classified into four groups: < 18.5, 18.5 - 24.9, 25-29.9, and > 29.9. Three diagnostic thresholds were used for myopia A\B\C: spherical equivalent <= -0.5\-0.75\-1 diopters in the right eye. Multivariate logistic regression analysis and smooth curve fitting were performed to evaluate the association between BMI and myopia.Results The incidence of myopia was 39.4%. BMI was correlated with myopia, with each 1 kg/m(2) increase in BMI associated with a 1% increase in the risk of myopia (OR, 1.01; 95% CI 1.01 1.02; p < 0.05). In myopia B, after adjusting for confounding factors, compared with the reference group (BMI 18.5-24.9), participants with a BMI of 25-29.9 and greater than 29.9 had a 14% and 25% increased risk of myopia, respectively (OR 1.14; 95% CI 1.01 1.29; p = 0.037, OR 1.25; 95% CI 1.08 1.44; p = 0.003), which was similar to the results for myopic A (OR, 1.15; 95% CI 1.02 1.3; p = 0.027, OR 1.19; 95% CI 1.03 1.37; p = 0.018) and myopia C (OR 1.15; 95% CI 1.01 1.31; p = 0.035, OR 1.18; 95% CI 1.01 1.37; p = 0.032). Moreover, there was a linear relationship between myopia and BMI (p for nonlinearity = 0.767).Conclusions Myopia using all three diagnostic thresholds was positively associated with higher BMI. This suggests a potential association between myopia and higher BMI in the American population, warranting further investigations.