Vitamin B12 and Cognitive Health: What Pharmacists Should Know

Vitamin B12, or cyanocobalamin, is an essential vitamin naturally produced by bacteria. It is chemically classified as a “corrinoid”, a family of compounds containing a cobalt-centered complex. Peak plasma concentrations are reached 1 hour after B12 injection and 8 to 12 hours after tablet ingestion. It is partially excreted in the urine and the gastrointestinal tract daily through bile and has a biological half-life of about 6 days. Vitamin B12 is primarily distributed in the tissues and stored in the liver and bone marrow to help improve red blood cell formation and decrease risks of major birth defects.^1,2

The Annals of Case Reports and Medical Images defines vitamin B12 deficiency as a B12 level under 200pg/mL.³ Deficiency of vitamin B12 leads to an increased risk of macular degeneration, osteoporosis, and memory loss. Individuals most likely at risk for vitamin B12 deficiency are older adults, people with Crohn’s or celiac disease, patients on long-term metformin, those taking proton pump inhibitors, and those on a strict vegetarian diet.²

Prescription B12 can be given in 3 forms:^4,5

1. Tablet: 25 to 2000mcg orally daily
2. Injectable: 100 to 200mcg intramuscular (IM) monthly
3. Nasal spray: 500mcg once weekly

When comparing oral and injectable B12 levels, normalization of serum levels are about the same.⁶ In a 2003 prospective case series, the patient sample was treated with IM B12, 1000mcg injections every 3 months with serum levels monitored at weeks 2,4, 8, and 12. When the serum levels reached the 25^th percentile, 418pg/mL, the patients were switched to oral B12. The study found that the serum B12 levels at the start of oral therapy increased and then normalized at 3 months, with no one meeting the criteria to restart IM B12 injections.⁶

In the presence of pneumococcal meningitis, B12 can ignite anti-inflammatory pathways that would otherwise be inhibited by the meningitis infection.⁷ Meningitis can cause cognitive deficits in survivors, affecting epigenetic regulation and host response. B12 can increase DNA methylation and positively alter histone methylation patterns. Ultimately, mitigating hippocampal damage and neuroinflammation seen in pneumococcal meningitis.⁷

It has also been found that patients with long COVID can develop visuoconstructive deficit (VCD)—defined in a study as “an impaired ability to visually perceive complex visual-spatial designs or tasks.”⁸ VCD is linked to upregulation of the CCL11 mRNA gene, which is associated with age-related cognitive decline, psychiatric disorders, Alzheimer disease, and multiple sclerosis (MS). B12 can normalize serum levels of the CCL11 gene through methyl-dependent epigenetic mechanisms.⁸

In conclusion, vitamin B12 is essential in various functions of the body and deficiency can lead to serious complications. So, the next time a customer comes in and asks, “what can I take over the counter for cognitive health?” Vitamin B12 should be one of your answers.

REFERENCES

1. National Center for Biotechnology Information. PubChem Compound Summary for CID 166596686, Cyanocobalamin. https://pubchem.ncbi.nlm.nih.gov/compound/Cyanocobalamin. Accessed January 19, 2026.

2. Berkhesier K, Bernstein A. Health benefits of vitamin B12, based on science. Healthline. Published January 30, 2024. Accessed January 21, 2026. https://www.healthline.com/nutrition/vitamin-b12-benefits

3. Andres E, Jannot X, Terrade JE, Villalba NL. Definition of vitamin B12 deficiency: Concepts, biomarkers, grey zones, subclinical states, and diagnostic perspectives. Ann Case Rep Med Images. 2025; 2(2): 1055. https://anncrmi.org/articles/CRMI-1055.pdf.

4. Cyanocobalamin dosage. Drugs.com. December 4, 2025. Accessed January 22, 2026. https://www.drugs.com/dosage/cyanocobalamin.html#Usual_Adult_Dose_for_B12_Nutritional_Deficiency

5. Vitamin B12, Athlete (cyanocobalamin) dosing, indications, interactions, adverse effects, and more. Medscape. July 15, 2024. Accessed January 22, 2026. https://reference.medscape.com/drug/vitamin-b12-nascobal-cyanocobalamin-344418?_gl=1*10luhg9*_gcl_au*MTg4MDc5NjM4LjE3NjQ4ODI5MDc.

6. Mounsey A, Brendle D, Flowers K. Oral vs. Intramuscular vitamin B12 for treating vitamin B12 deficiency. American Family Physician. 2022;105(6):663-664. Accessed January 21, 2026. file:///C:/Users/Juvaria/Downloads/b12%20deificency%20article.pdf.

7. Cassiano LMG, Oliveira MdS, de Queiroz KB, et al. Uncovering the neuroprotective effect of vitamin B12 in pneumococcal meningitis: insights into its pleiotropic mode of action at the transcriptional level. Front. Immunol. 14:1250055. doi: 10.3389/fimmu.2023.1250055.

8. Cassiano LMG, de Paula JJ, Rosa DV, Miranda DM, Romano-Silva MA, Coimbra RS. Vitamin B12 as an epidrug for regulating peripheral blood biomarkers in long COVID-associated visuoconstructive deficit. Sci Rep. March 19, 2025. doi: 10.1038/s41598-025-86637-0