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 tissues and stored in the liver and bone marrow to help improve red blood cell formation and decrease the risk of major birth defects.^1,2

The Annals of Case Reports and Medical Images defines vitamin B₁₂ deficiency as a B₁₂ level under 200 pg/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 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 200 μg orally daily
2. Injectable: 100 to 200 μg intramuscular (IM) monthly
3. Nasal spray: 500 μg once weekly

When comparing oral and injectable B₁₂ levels, normalization of serum levels is about the same.⁶ In a 2003 prospective case series, the patient sample was treated with IM B₁₂, 1000-μg injections every 3 months with serum levels monitored at weeks 2,4, 8, and 12. When the serum levels reached the 25th percentile, 418 pg/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. B₁₂ can normalize serum levels of the CCL11 gene through methyl-dependent epigenetic mechanisms.⁸

In conclusion, vitamin B₁₂ is essential for 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. Cyanocobalamin. PubChem. Accessed January 19, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/Cyanocobalamin

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

3. Andres E, Jannot X, Terrade JE, Lorenzo-Villalba N. Definition of vitamin B12 deficiency: concepts, biomarkers, grey zones, subclinical states, and diagnostic perspectives. Ann Case Rep Med Images. 2025;2(2):1055.

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

5. Cyanocobalamin (Rx, OTC). Medscape. July 15, 2024. Accessed January 22, 2026. https://reference.medscape.com/drug/vitamin-b12-nascobal-cyanocobalamin-344418#0

6. Mounsey A, Brendle DC, Flowers K. Oral vs. intramuscular vitamin B12 for treating vitamin B12 deficiency. Am Fam Physician. 2022;105(6):663-664. Accessed January 21, 2026.

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. 2023;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. 2025;15(1):9438. doi:10.1038/s41598-025-86637-0