Mapping the Evidence on Vitamin D, Vitamin B12, and Folate Deficiencies and Their Potential Impact on Treatment Outcomes in Patients With Cancer in Sub-Saharan Africa: Protocol for a Scoping Review.

BACKGROUND

Micronutrient deficiencies, particularly of vitamin D, vitamin B12, and folate, are increasingly recognized as important, yet underexplored contributors to adverse outcomes in oncology care. These micronutrients are essential for immune regulation, DNA synthesis and repair, cell proliferation, and metabolic homeostasis, all of which are frequently disrupted in patients with cancer. Deficiencies may arise due to cancer-related metabolic changes, malabsorption, anorexia, and treatment-related toxicities, potentially influencing therapeutic response, treatment tolerance, survival, and quality of life. Despite growing evidence, findings remain fragmented across cancer types, treatment modalities, and geographical settings.

OBJECTIVE

This scoping review aims to systematically map the available evidence on the prevalence, determinants, and reported clinical associations of vitamin D, vitamin B12, and folate deficiencies among adult patients with cancer. The review will also explore how these deficiencies are associated with treatment-related outcomes, including toxicity, therapeutic response, survival, hospitalization, and quality of life, and will identify reported screening, supplementation, and nutritional management practices in oncology care.

METHODS

The review protocol follows the Joanna Briggs Institute methodology for scoping reviews and will be reported according to the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews). A comprehensive search of PubMed and MEDLINE, Scopus, ScienceDirect, and relevant gray literature sources will be conducted for studies published between 2000 and 2025. Eligible studies will include observational, interventional, mixed methods, and qualitative studies examining vitamin D, vitamin B12, and/or folate deficiencies in adult oncology populations. Two reviewers will independently screen studies, extract data, and chart findings, whereas a third reviewer will resolve disagreements. Extracted data will include prevalence estimates, determinants of deficiencies, clinical outcomes, and nutritional management strategies. Findings will be synthesized descriptively and presented using thematic mapping, summary tables, and evidence charts.

RESULTS

A preliminary search was conducted in May 2026. Study selection commenced on June 30, 2026, following the completion of database searches and removal of duplicate records and was finalized within 8 weeks by August 30, 2026. The anticipated timelines for each stage of the review are presented in the Results section below. Preliminary search outputs from the PubMed database demonstrate the feasibility of the proposed search strategy. The final review will report the number of studies identified, screened, included, and excluded at each stage using a PRISMA-ScR flow diagram.

CONCLUSIONS

The scoping review is expected to inform future systematic reviews, guide clinical research priorities, and support the integration of nutritional assessment and monitoring into personalized oncology care, particularly in resource-limited settings.