Dietary iron intake is nonlinearly associated with the risk of diabetic retinopathy in adults with type 2 diabetes.

OBJECTIVE

To elucidate the association between dietary iron intake and diabetic retinopathy (DR) in type 2 diabetes (T2D) patients.

METHODS

Participants from the National Health and Nutrition Examination Survey (NHANES) 2005-2008 aged over 40 years with T2D were included. Dietary iron intake was estimated from standardised questionnaires. The presence of DR and vision-threatening DR (VTDR) was determined through retinal imaging. We used logistic regression to assess the relationship between iron intake and DR, and restricted cubic splines to reveal nonlinear links.

RESULTS

The study enrolled 1172 T2D adults. We found significant nonlinear associations between dietary iron intake and DR among females (P = 0.023), but not in males (P = 0.490). Compared with the lowest quartile of iron intake, the third quartile (13.2-18.1 mg/d) yielded significantly lower odds of developing DR (odds ratio [OR], 0.59; 95% CI, 0.39-0.90) and VTDR (OR, 0.42; 95% CI, 0.19-0.94). Stratified logistic analyses showed that medium-high iron intake was associated with lower risks of DR in females (OR, 0.44; 95% CI, 0.24-0.81), non-Hispanic Blacks (OR, 0.38; 95% CI, 0.17-0.85), and individuals with obesity (OR, 0.45; 95% CI, 0.25-0.82), high HbA1c (OR, 0.56; 95% CI, 0.34-0.93), long diabetes duration (OR, 0.40; 95% CI, 0.21-0.76) or low blood haemoglobin (OR, 0.17; 95% CI, 0.05-0.60).

CONCLUSION

Dietary iron intake was nonlinearly negatively associated with the prevalence of DR and VTDR, showing protective effect against retinopathy of medium-high iron intake in T2D patients. Such associations significantly vary by multiple factors such as age, ethnicity, obesity and glycaemic control.