In a report on oral iron supplements, the IRONOUT HF study, which targeted 225 HFrEF patients with iron deficiency, found no significant difference between the oral iron supplement group and the placebo group in terms of peak VO2 (p = 0.46), 6-min walk distance (p = 0.19), NT-proBNP levels (p = 0.48), or KCCQ clinical scores (p = 0.57) [16]. This evidence concerns the gene NPPB and nutritional disorder.