Associations Between Micronutrients and Red Cell Distribution Width in Adults: A Scoping Review

This scoping review was performed to analyze the available evidence on the association between micronutrient status and red cell distribution width (RDW) in adults. As a measure of erythrocyte size variability (anisocytosis), RDW has emerged as a prognostic biomarker in diverse diseases. It is hypothesized that nutritional factors may influence RDW, leading to decreased variability of red cell size and thereby enhancing the stability and lifespan of the red blood cell. However, to our knowledge no comprehensive review has yet examined how micronutrition may affect RDW in adult populations without conditions that are known to increase anisocytosis. This review was performed to improve understanding of how micronutrition may affect RDW through a scoping review protocol following the PRISMA-ScR framework and explore the literature that describes the use of and outcomes of supplementation. A comprehensive literature search was conducted in February 2025, and after peer review, the Critical Appraisal Skills Programme (CASP) appraisal tool was used to assess the rigor of each study design. The scoping review identified 10 articles that met the inclusion criteria. These studies examined a range of nutrients, including vitamins A, D, and E, carotenoids, omega-3 fatty acids, selenium, and dietary fiber. Several studies suggested that higher micronutrient status or supplementation is associated with lower RDW values. However, study designs and findings were variable and not uniform across all nutrients. Some nutrients (eg, vitamin A, vitamin E) showed no significant associations in individual studies, and 1 trial reported no change in RDW with an algae-based supplement. Results of this review indicated that micronutrition can have a measurable influence on RDW, suggesting a possible nutritional approach to modulate this emerging hematologic biomarker. Optimizing micronutrient intake could contribute to lower RDW, although the current evidence is preliminary. Further research is needed to confirm if these associations have longstanding effects to reduce RDW and determine whether improving micronutrient status can translate into better health outcomes.