What are the symptoms of Vitamin B12 deficiency?

From the Guidelines

Vitamin B12 deficiency can cause a range of symptoms including abnormal findings on a blood count, cognitive difficulties, and eyesight problems related to optic nerve dysfunction, such as blurred vision, as outlined in the most recent guideline summary from 2024 1. These symptoms develop gradually as B12 levels decline and can worsen over time. The deficiency affects multiple body systems because B12 is essential for red blood cell formation, neurological function, and DNA synthesis.

• Common symptoms and signs of vitamin B12 deficiency include:
  • Abnormal findings, such as anaemia or macrocytosis, on a blood count
  • Cognitive difficulties, such as difficulty concentrating or short term memory loss
  • Eyesight problems related to optic nerve dysfunction, such as blurred vision According to the latest guidelines, treatment typically involves B12 supplementation, with the route depending on the cause and severity of the deficiency, and people with absorption issues may require lifelong supplementation 1.
• Treatment options for vitamin B12 deficiency include:
  • Hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement, then administer hydroxocobalamin 1 mg intramuscularly every 2 months for people with neurological involvement
  • Hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks for people with no neurological involvement
  • Maintenance treatment with 1 mg intramuscularly every 2–3 months lifelong after treatment of vitamin B12 deficiency.

From the FDA Drug Label

CLINICAL PHARMACOLOGY Vitamin B12 is essential to growth, cell reproduction, hematopoiesis, and nucleoprotein and myelin synthesis. Intrinsic factor deficiency causes pernicious anemia, which may be associated with subacute combined degeneration of the spinal cord Prompt parenteral administration of vitamin B12 prevents progression of neurologic damage.

The symptoms of B12 deficiency include pernicious anemia and subacute combined degeneration of the spinal cord.

• Pernicious anemia is caused by intrinsic factor deficiency.
• Subacute combined degeneration of the spinal cord is a neurologic damage that can be prevented by prompt parenteral administration of vitamin B12 2.

From the Research

Symptoms of B12 Deficiency

The symptoms of B12 deficiency are not explicitly stated in the provided studies. However, the studies discuss the importance of prompt diagnosis and treatment of B12 deficiency, suggesting that it can have significant clinical implications if left untreated.

Diagnosis of B12 Deficiency

• The diagnosis of B12 deficiency can be complex, and several biomarkers are used to detect it, including vitamin B12, holotranscobalamin, methylmalonic acid, and homocysteine 3, 4, 5, 6, 7.
• The studies suggest that a single biomarker may not be sufficient to diagnose B12 deficiency, and a combination of markers may be more accurate 5, 6, 7.
• The use of a diagnostic testing cascade is recommended to improve compliance and accuracy in diagnosing B12 deficiency 5.

Biomarkers for B12 Deficiency

• Methylmalonic acid (MMA) and homocysteine (HC) have been identified as better indicators of B12 deficiency than serum vitamin B12 levels alone 6.
• Holotranscobalamin (HoloTC) has been suggested as a preferred first-line marker for detecting subclinical B12 deficiency in women 50 years and older 7.
• The diagnostic accuracy of these biomarkers can vary depending on the population being studied and the cutoff values used 6, 7.

Clinical Implications

• B12 deficiency can have significant clinical implications if left untreated, including hematologic and neurologic responses 5.
• A thorough clinical assessment is important to identify patients who may have risk factors and/or symptoms suggestive of B12 deficiency 6.