Blood glucose control, magnesium status, and diabetic retinopathy in patients with type 2 diabetes mellitus: Evidence from NHANES 2005–2018

Objective This study sought to explore the association of magnesium (Mg) status and blood glucose control, represented by Mg depletion score (MDS) and hemoglobin A1c (HbA1c) level, respectively, with the risk of diabetic retinopathy (DR) among type 2 diabetes mellitus (T2DM) patients, and whether there were interactions between Mg status and blood glucose control on the risk of DR. Methods Data of this cross-sectional study were extracted from the National Health and Nutrition Examination Surveys (NHANES) database 2005–2018. MDS was an indicator to assess the overall Mg status in the human body that considers the pathophysiological factors influencing the kidneys’ reabsorption capability. Blood glucose control was represented by hemoglobin A1c (HbA1c) and HbA1c level ≥7% referred to poor blood glucose control. Receiver Operating curve (ROC) analysis was performed to evaluate the predictive performance of MDS and HbA1c for DR. Weighted univariate and multivariate analyses were utilized to explore the MDS and HbA1c and their interactions effects on the risk of DR, with odds ratios (ORs), 95% confidence intervals (CIs), relative excess risk due to interactions (RERI) and attributable proportion due to interactions (AP). These interactions were further explored based on the age, gender, and cardiovascular disease (CVD) history. Results A total of 4487 T2DM patients were included, of whom 942 (20.99%) had DR. After covariate adjustment, both high MDS (≥2) and elevated HbA1c levels (≥7%) demonstrated significant independent associations with increased DR risk. ROC analysis showed MDS (AUC = 0.766) and HbA1c (AUC = 0.749) in fully adjusted models. Significant interactions between MDS and HbA1c amplified DR risk beyond individual effects, with this pattern most pronounced among female patients, those aged ≥60 years, and individuals with a cardiovascular disease history. Conclusions The results of this study suggested that high MDS as well as high HbA1c level may have interaction effects on the high risk of DR among T2DM patients.