Iron, vitamins and supplements

Article written and reviewed by Dr Luca Moretti

In advanced management of anemia, correction of documented deficiencies of iron, vitamin B12 and folate is essential to restore effective erythropoiesis and, when relevant, optimize response to subsequent therapeutic strategies such as erythropoiesis stimulating agents. In the era of personalized medicine, choice of agent, route of administration, dose and monitoring of supplementation require extremely refined clinical reasoning and continuous integration of laboratory data, clinical findings, comorbidities and response to ongoing therapies. The contemporary approach to supplementation is based on several key principles:

• Precise and updated assessment of iron and vitamin status is essential for promptly identifying deficiencies and planning truly targeted intervention while avoiding both underestimation and the risk of overtreatment and overload.
• Personalization of supplementation requires selection among multiple agents and routes of administration, taking into account drug interactions, inflammation, intestinal absorption and the need for more or less rapid correction.
• Advanced monitoring of treatment response cannot be limited to hemoglobin assessment. It requires integrated interpretation of storage parameters, inflammatory markers and dynamic clinical data, also to identify resistance and complications early.
• Iron and vitamin supplementation should be incorporated into a broader treatment algorithm that includes management of underlying causes, support for stimulating therapies and, when necessary, planning of transfusion strategies and use of emerging medications.

These principles apply in all clinical settings, from uncomplicated iron deficiency anemia to patients on dialysis, patients receiving chemotherapy, pregnancy at risk and critically ill or surgical patients.

Iron therapy

Correction of iron deficiency now requires a rigorously evidence based approach founded on detailed understanding of available agents, routes of administration and specific features of the main clinical settings. Choice between oral and parenteral supplementation should not be empirical but should follow defined indications, specialist algorithms and multidisciplinary assessment.

Oral iron:

Oral iron is first line treatment for uncomplicated iron deficiency when absorption and the clinical timeframe allow it. BSG guidelines recommend initially one tablet daily of ferrous sulfate, fumarate or gluconate; alternate day administration is an option particularly in case of intolerance or according to individualized prescription.
Specialist monitoring generally includes assessment of hemoglobin response within 2 to 4 weeks. Ferritin and transferrin saturation should be rechecked at a time appropriate to the context and route of administration, avoiding premature interpretation especially after intravenous iron. Failure to respond, such as less than a 1 g/dL increase in hemoglobin in one month of iron therapy, requires diagnostic reassessment and exclusion of concomitant factors including occult losses, inflammation, malabsorption and poor adherence.

Intravenous iron

Parenteral supplementation is indicated when oral iron is contraindicated, ineffective or not tolerated, in malabsorption, persistent losses or when rapid correction is required. Nephrology, oncology, inflammatory bowel disease, pregnancy and surgery require specific criteria and are not in themselves universal indications.
The maximum dose per infusion depends on the preparation, body weight and corresponding product information. Formulations differ in infusion time and hypersensitivity profile; serious reactions remain rare but require appropriate surveillance.
The total dose is calculated according to estimated requirements using the Ganzoni formula or setting specific guidelines, including nephrology, oncology and surgery. In hemodialysis patients, intravenous iron is generally preferred; oral administration may be considered in selected cases but is often less effective.

Special settings:

In nephrology , intravenous supplementation is integrated into erythropoiesis stimulation protocols, with monitoring of transferrin saturation and ferritin and thresholds for initiation or withholding adapted to disease stage and clinical context, without universal iron targets.
In oncology , intravenous iron may be used in selected patients with absolute or functional deficiency, particularly within ESA protocols; it is not recommended indiscriminately for all chemotherapy associated anemia.
In obstetrics , intravenous iron may be considered, generally after the first trimester, when oral iron is ineffective or not tolerated or when rapid correction is required.
In surgery , correction of iron deficiency is part of patient blood management programs and may reduce transfusion use in selected patients; the benefit for postoperative outcomes depends on the population, timing and protocol.

Management of adverse effects and iron overload:

Iron surveillance should be adapted to the setting; there is no universal threshold for withholding treatment. In chronic kidney disease, KDIGO 2026 suggests temporarily withholding routine iron when ferritin is above 700 ng/mL or TSAT is at least 40%, except in selected clinical circumstances; other conditions use specific criteria.
Adherence, correct selection of route of administration, individualized dosing and multidimensional monitoring are the cornerstones of specialist iron therapy.

Vitamin B12 therapy

Vitamin B12 (cobalamin) is indicated in documented deficiency or conditions at high risk of deficiency; pregnancy, chronic hemolysis and dialysis alone are not indications for supplementation. Administration should be planned according to the clinical picture, severity of deficiency, presence of neurologic symptoms and pathophysiologic context, with the utmost attention to the choice of route of administration and prevention of complications.

Route of administration and available formulations:

The route of vitamin B12 administration depends on the cause, severity, presence of neurologic symptoms, adherence and authorized formulations. Oral or intramuscular administration is used mainly according to guidelines and product information.

Treatment protocols:

Vitamin B12 dosage varies according to formulation, cause and national guidelines. Specific parenteral regimens are used for deficiencies due to malabsorption or with neurologic manifestations; high oral doses may be effective in dietary deficiency or selected patients. Maintenance is lifelong only when an irreversible cause persists.

Management in special settings:

• Neurology: in patients with acute neurologic signs such as paresthesias, ataxia or demyelination, rapid correction is a priority to prevent irreversible injury. In severe deficiency or neurologic manifestations, vitamin B12 regimens are defined by cause and applicable guidelines, often using intramuscular administration. Monitoring is primarily clinical and laboratory based, with neurophysiologic testing only when indicated.
• Geriatrics and multimorbidity: vitamin B12 deficiency should be documented and its cause investigated. Oral or intramuscular administration is selected according to malabsorption, severity, adherence and preferences, not age alone.
• Oncology and dialysis: supplementation is indicated only in documented deficiency or as part of a specific therapeutic protocol.
• Pregnancy and postpartum period: correction of deficiency is essential to prevent adverse fetal and maternal outcomes. Requirements increase in advanced pregnancy and lactation; oral administration is generally adequate unless malabsorption is documented.

Monitoring and assessment of response:

Treatment efficacy is assessed by clinical improvement and hematologic response, including complete blood count and reticulocytes as appropriate. Reticulocytosis generally begins within the first days, while hemoglobin and MCV correct over subsequent weeks. Serum vitamin B12 should not be used as a general response criterion and should not be routinely repeated in patients receiving intramuscular therapy because supplementation can raise the level independently of functional correction. Persistent neurologic symptoms require diagnostic reassessment and exclusion of irreversible injury or combined deficiencies such as folate or copper.

Complications, risks and limitations:

Before treating possible folate deficiency, vitamin B12 deficiency should be excluded or treated concurrently because folic acid may correct the anemia while masking neurologic progression. Folate need not be delayed when both deficiencies are treated appropriately.
In patients with conditions that confer a risk of chronic malabsorption, supplementation should be prolonged or, in some cases, lifelong, with periodic clinical and laboratory reassessment. For further details on management of resistant forms or associated neurologic complications, see the section on vitamin B12 deficiency anemia.

Folate therapy

Folate supplementation is indicated for documented deficiency and in specific preventive situations or states of increased requirement. During pregnancy, folic acid is used for prevention according to risk profile; in chronic hemolysis and dialysis, the indication depends on diet, losses and documentation of deficiency. In oncology protocols with high dose methotrexate, folinic acid, or leucovorin, is used as rescue according to the regimen; in low dose regimens, folic acid is commonly used according to indication. 5 fluorouracil is not a general indication for folic acid supplementation.

Choice of agent, route of administration and dosage:

Folic acid is given predominantly orally, but dose and duration depend on the indication. Standard preconception prophylaxis is 400 micrograms daily, whereas treatment of deficiency and high risk regimens use different doses according to guidelines. Doses of 5 to 15 mg daily are not appropriate as a general regimen.

Specific clinical settings:

• Pregnancy and prevention of neural tube defects: 400 micrograms daily from the preconception period in standard risk women. Doses of 4 to 5 mg daily are reserved for defined high risk conditions, such as a previous pregnancy affected by a neural tube defect, according to national guidance.
• Chronic hemolysis: continuous supplementation may be considered when diet, requirements and laboratory data indicate risk or deficiency; high doses are not automatic.
• Chronic dialysis: folate supplementation at moderate or high doses is not routine and should be reserved for documented deficiency or specific protocols.
• Oncology: during chemotherapy protocols with antimetabolites, folinic acid, or leucovorin, is used as rescue to limit bone marrow toxicity induced by methotrexate and other antifolate agents.

Advanced strategies and management of resistance:

If there is no response to folate, the diagnosis, adherence, malabsorption, combined B12 deficiency, alcohol use and folate antagonist medications, particularly some anticonvulsants, should be reassessed. Antacids are not a generally documented cause of failure of folate therapy.

Treatment risks and monitoring:

The main risk of inappropriate folate supplementation is masking hematologic manifestations of concomitant vitamin B12 deficiency while neurologic complications of untreated vitamin B12 deficiency may progress. Specialist monitoring includes clinical and hematologic response and, when useful, folate levels. Serum vitamin B12 should not be routinely repeated as a measure of response during effective supplementation, especially intramuscular treatment. Clinical surveillance for symptoms suggestive of neuropathy remains essential.

Practical conclusions:

Correction of folate deficiency restores erythropoiesis when deficiency is causal. Maternal fetal prevention and use in oncology or nephrology require specific indications and protocols rather than generalized supplementation.

Management of inadequate response and integration with advanced therapeutic strategies

Failure to achieve treatment goals after supplementation with iron, vitamin B12 or folate is one of the most complex challenges in modern hematology. A suboptimal response, defined as absence of a significant increase in hemoglobin, for example less than 1 g/dL in 4 weeks of iron therapy, requires activation of a second level diagnostic and treatment algorithm aimed not only at restoring deficiencies but also at correcting interfering factors and underlying disorders.

Practical specialist reassessment algorithm:

• Verify adherence and correct administration: review dose and specific interactions, including acid suppression for iron or B12, metformin for B12 and anticonvulsants for folate. Oral antibiotics are not a general category causing malabsorption.
• Investigate intestinal malabsorption: perform targeted testing for celiac disease, villous atrophy, resections and parasitic infections, especially when response to oral therapy is absent or transient.
• Identify occult blood loss: endoscopic investigations, assessment for gynecologic or urinary bleeding and evaluation of chronic vascular disorders, especially in older patients.
• Exclude combined deficiencies: measure iron, vitamin B12 and folate concurrently and, when necessary, copper, zinc and vitamin C.
• Assess chronic inflammatory status: measure CRP, ESR, alpha1 acid glycoprotein and ferritin using an appropriately higher cutoff; in anemia of chronic disease, supplementation should be integrated with management of the underlying disorder.
• Screen for primary or secondary bone marrow disorders: consider myelodysplasia, bone marrow infiltration, malignancy, chronic viral infections and myelotoxic medications.

Integration with stimulating therapies and transfusion strategies:

In patients with inadequate response despite appropriate supplementation, adding erythropoietin or analogs, or using blood transfusions , should be considered according to the clinical picture, severity of symptoms and prospects for hematologic recovery. The combined approach should be individualized by integrating laboratory data, clinical signs and quality of life.

Role of additional supplements and current controversies:

Supplementation with vitamin C to optimize iron absorption, copper and zinc is indicated only for documented deficiencies or in patients receiving prolonged parenteral nutrition, after extensive bariatric surgery or with severe chronic disease at risk of multiple deficiencies. Empirical supplementation is not recommended by international guidelines and may in some cases impair absorption of other micronutrients or cause toxicity.

Pharmacoeconomics, adherence and prevention of errors:

Optimal management of supplementation also requires attention to cost effectiveness, including choice of agent, route of administration and monitoring frequency, patient adherence through education and management of adverse effects, and prevention of risks from overtreatment or undertreatment, particularly in chronic or multimorbid settings.

In summary, specialist monitoring, rapid identification of causes of inadequate response and rational integration with advanced therapeutic strategies are the pillars of effective and safe treatment of iron, vitamin B12 and folate deficiency anemias.

Practical conclusions

Therapeutic management of deficiencies of iron, vitamin B12 and folate now requires a highly specialist approach based on careful selection of agents, personalization of routes of administration, multidimensional monitoring of response and continuous assessment of the risks of over or undertreatment. Rational integration of these micronutrients into a treatment algorithm that considers comorbidities, inflammation, drug interactions and the need for synergy with other antianemic strategies is key to achieving stable hematologic recovery, preventing complications and optimizing prognosis across the main clinical settings.

Only mastery of the most current protocols, the ability to adapt therapy to dynamic patient responses and active surveillance for adverse effects and resistance can achieve outcomes comparable with those of leading international referral centers. Iron, vitamin B12 and folate supplementation should therefore be regarded not as a routine prescribing act, but as a strategic component of precision hematology.

Bibliography
1. Snook J, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. 2021;70(11):2030–2051.
2. World Health Organization. Guideline: Daily iron supplementation in adult women and adolescent girls. Geneva: WHO. 2016.
3. Camaschella C. Iron-deficiency anemia. N Engl J Med. 2015;372(19):1832–1843.
4. Kidney Disease: Improving Global Outcomes Anemia Work Group. KDIGO 2026 Clinical Practice Guideline for the Management of Anemia in Chronic Kidney Disease. Kidney Int. 2026;109(1S):S1–S99.
5. National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239. 2024.
6. O’Leary F, Samman S. Vitamin B12 in health and disease. Nutrients. 2010;2(3):299–316.
7. Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149–160.
8. Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood. 2017;129(19):2603–2611.
9. Fletcher A, Forbes A, Svenson N, Thomas DW; British Society for Haematology. Guideline for the laboratory diagnosis of iron deficiency in adults (excluding pregnancy) and children. Br J Haematol. 2022;196(3):523–529.
10. Devalia V, Hamilton MS, Molloy AM. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. 2014;166(4):496–513.