Choosing the Best Vitamin B12 for Energy and Brain Health

Low energy. Tingling or numbness in the feet. Brain fog. Poor balance.

These are just a few possible symptoms of low vitamin B12. Some signs are subtle and may be overlooked, potentially resulting in serious damage.¹

Taking oral B12 may help provide a safety net by ensuring adequate B12 status.² However, not all forms are the same.

Only two types of B12 are active in cells:

Adenosylcobalamin and Methylcobalamin.³

These bioactive forms may help address common age-related conditions, including neurological dysfunction:

• In preclinical models of Parkinson's disease, adenosylcobalamin helped protect dopa mine-producing neurons.⁴
• In a human study, oral methylcobalamin was associated with improvements in nerve pain in adults with diabetic peripheral neuropathy, which is commonly experienced by people with diabetes.⁵

Together, oral methylcobalamin and adenosylco balamin can help optimize the body's vitamin B12 status

The Importance of B12

Vitamin B12 is critical for the development and maintenance of the central nervous system. A deficiency can lead to neurological concerns, including nerve damage, balance issues, cognitive impairment, and dementia.⁶

Vitamin B12 is found primarily in foods of animal origin, including meat, poultry, some eggs, and dairy products.⁷

The need for supplementation is rising as more people move to plant-based diets,^8,9 and due to the decreased absorption of food-based B12, which many people face as they age.^8-10

Two bioactive forms of vitamin B12 are:

• Adenosylcobalamin, which is active in the mitochondria, the energy powerhouse within each cell,¹¹ and
• Methylcobalamin, which is active in the cytosol (gel-like fluid) inside the body's cells.^11,12

B12 is needed to form healthy red blood cells, DNA, and the myelin covering of nerves.^12,13

Some individuals have genetic variants that can impair the body's ability to convert vitamin B12 into its active forms. That may make the bioactive B12 forms preferable.¹⁴

People generally don't know their B12-related genetics. Oral intake of both adenosylcobalamin and methylcobalamin may help support B12 levels.¹⁴

Adenosylcobalamin Against Parkinson's Disease

Low levels of vitamin B12 have been associated with progression of Parkinson's disease.¹⁵

Parkinson's involves the progressive loss of neurons that produce the neurotransmitter dopamine in the brain.¹⁶ This gradually impairs muscle control, balance, mobility, and cognitive function.¹⁷

A mutation resulting in overactivity of the LRRK2 enzyme and destruction of dopamine-producing neurons is a top genetic cause of Parkinson's disease.¹⁸

In preclinical research, scientists discovered that adenosylcobalamin inhibited LRRK2 activity and reduced markers of neurotoxicity in experimental models involving dopamine neurons.⁴

In these studies, scientists tested adenosylcobalamin in roundworms genetically modified to express the LRRK2 gene mutation. These worms exhibited symptoms (age-dependent dopaminergic neurodegeneration and behavioral deficits) similar to human Parkinson's disease.⁴

When the young worms were given adenosylcobalamin, it prevented the destruction of dopamine neurons and related symptoms when they became adults. Similar neuroprotection was found in fruit flies.

In mice, adenosylcobalamin alleviated deficits in dopamine release sustainability caused by LRRK2 disease variants.⁴

Methylcobalamin and Neurological Health

Older adults with elevated levels of homocysteine are at increased risk of stroke¹⁹ and dementia.^20,21

Vitamin B12 serves as a cofactor to help lower homocysteine levels.^22,23

Clinical (human) research has shown benefits of methylcobalamin for diabetic peripheral neuropathy, a condition marked by painful tingling, burning, or hot/cold sensations in the arms, legs, hands, and feet.⁵

Peripheral neuropathy commonly affects people with diabetes and can occur in prediabetes.²⁴ The nerve pain and other symptoms can also be triggered by physical injuries²⁵ and insufficient vitamin B12 levels.^25,26

In a one-year clinical trial, researchers gave 1,000 mcg of oral methylcobalamin or a placebo daily to 90 adults with type 2 diabetes who had diabetic neuropathy and vitamin B12 blood levels below 400 picomoles (pmol)/L.⁵

All subjects had been taking metformin—a diabetes drug that can impair B12 absorption—for at least four years. In the methylcobalamin group, neuropathy pain scores significantly improved, while the placebo group's pain scores significantly worsened.

In addition, the B12 treatment group raised their serum B12 levels from 232.0 pmol/L at baseline to 776.7 pmol/L. B12 levels did not significantly change in the placebo group.⁵

Though vitamin B12 levels below 148 pmol/L are typically used as the threshold for diagnosing deficiency,²⁷ neurological dysfunction can occur even in individuals with levels higher than this.^27,28

A randomized, double-blind, placebo-controlled trial enrolled patients with type 2 diabetes on metformin who had B12 levels below 400 pmol/L and demonstrated that B12 supplementation improved neuropathy outcomes, suggesting that even levels considered "sufficient" by conventional standards may be suboptimal in this population.⁵

Additional research published in 2025 found that even vitamin B12 levels within the normal range were linked to markers of neurological injury and reduced function in healthy older adults, suggesting that current definitions of optimal B12 levels may need to be re-evaluated.²⁸

Oral intake of 1,000 mcg of a combination of adenosylcobalamin and methylcobalamin may help support vitamin B12 status and neurological health.

Summary

Vitamin B12 is critical for maintaining neurological health and other essential functions.

Several forms of oral vitamin B12 are available. Methylcobalamin and adenosylcobalamin are the two forms used directly by enzymes in the body.

Preclinical data show that adenosylcobalamin may help preserve dopamine levels. Loss of dopamine is tied to the development of Parkinson's disease.

In a clinical study, oral methylcobalamin improved peripheral neuropathy pain in adults with diabetic peripheral neuropathy.

Combining these two bioactive forms of B12 may help support optimal levels for brain and nerve function, as well as overall health.

If you have any questions on the scientific content of this article, please call a Life Extension Wellness Specialist at 1-866-864-3027.

References

1. Wolffenbuttel BHR, McCaddon A, Ahmadi KR, et al. A Brief Overview of the Diagnosis and Treatment of Cobalamin (B12) Deficiency. Food Nutr Bull. 2024 Jun;45(1_suppl):S40-S9.
2. Available at: https://www.aafp.org/afp/2025/0900/vitamin-b12-deficiency. Accessed June 22, 2026.
3. Behringer CR, Kulkarni A, Weinstein A. Vitamin B12: A Comprehensive Review of Natural vs Synthetic Forms of Consumption and Supplementation. Cureus. 2025 Nov;17(11):e96258.
4. Schaffner A, Li X, Gomez-Llorente Y, et al. Vitamin B(12) modulates Parkinson's disease LRRK2 kinase activity through allosteric regulation and confers neuroprotection. Cell Res. 2019 Apr;29(4):313-29.
5. Didangelos T, Karlafti E, Kotzakioulafi E, et al. Vitamin B12 Supplementation in Diabetic Neuropathy: A 1-Year, Randomized, Double-Blind, Placebo-Controlled Trial. Nutrients. 2021 Jan 27;13(2).
6. Green R, Allen LH, Bjorke-Monsen AL, et al. Vitamin B(12) deficiency. Nat Rev Dis Primers. 2017 Jun 29;3:17040.
7. Available at: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/#:~:text=Vitamin%20B12%20is%20present%20in,bioavailability%20%5B13%2C14%5D. Accessed June 23, 2026.
8. Niklewicz A, Smith AD, Smith A, et al. The importance of vitamin B(12) for individuals choosing plant-based diets. Eur J Nutr. 2023 Apr;62(3):1551-9.
9. Allen LH. Micronutrients - Assessment, Requirements, Deficiencies, and Interventions. N Engl J Med. 2025 Mar 6;392(10):1006-16.
10. Andrès E, Terrade JE, Alonso Ortiz MB, et al. Unraveling the Enigma: Food Cobalamin Malabsorption and the Persistent Shadow of Cobalamin Deficiency. J Clin Med. 2025 Apr 8;14(8).
11. Mascarenhas R, Gouda H, Ruetz M, et al. Human B(12)-dependent enzymes: Methionine synthase and Methylmalonyl-CoA mutase. Methods Enzymol. 2022;668:309-26.
12. Calderon-Ospina CA, Nava-Mesa MO. B Vitamins in the nervous system: Current knowledge of the biochemical modes of action and synergies of thiamine, pyridoxine, and cobalamin. CNS Neurosci Ther. 2020 Jan;26(1):5-13.
13. Stabler SP. Clinical practice. Vitamin B12 deficiency. N Engl J Med. 2013 Jan 10;368(2):149-60.
14. Paul C, Brady DM. Comparative Bioavailability and Utilization of Particular Forms of B(12) Supplements With Potential to Mitigate B(12)-related Genetic Polymorphisms. Integr Med (Encinitas). 2017 Feb;16(1):42-9.
15. Rekik A, Santoro C, Poplawska-Domaszewicz K, et al. Parkinson's disease and vitamins: a focus on vitamin B12. J Neural Transm (Vienna). 2024 Dec;131(12):1495-509.
16. Bloem BR, Okun MS, Klein C. Parkinson's disease. Lancet. 2021 Jun 12;397(10291):2284-303.
17. Tanner CM, Ostrem JL. Parkinson's Disease. N Engl J Med. 2024 Aug 1;391(5):442-52.
18. De Wit T, Baekelandt V, Lobbestael E. LRRK2 Phosphorylation: Behind the Scenes. Neuroscientist. 2018 Oct;24(5):486-500.
19. Gueant JL, Gueant-Rodriguez RM, Oussalah A, et al. Hyperhomocysteinemia in Cardiovascular Diseases: Revisiting Observational Studies and Clinical Trials. Thromb Haemost. 2023 Mar;123(3):270-82.
20. Goldstein LB, Adams R, Alberts MJ, et al. Primary Prevention of Ischemic Stroke. Stroke. 2006 2006/06/01;37(6):1583-633.
21. Wu X, Zhou Q, Chen Q, et al. Association of homocysteine level with risk of stroke: A dose-response meta-analysis of prospective cohort studies. Nutr Metab Cardiovasc Dis. 2020 Oct 30;30(11):1861-9.
22. Sohouli MH, Almuqayyid F, Alfardous Alazm A, et al. A comprehensive review and meta-regression analysis of randomized controlled trials examining the impact of vitamin B12 supplementation on homocysteine levels. Nutr Rev. 2024 May 10;82(6):726-37.
23. Freeman AM, Morris PB, Aspry K, et al. A Clinician's Guide for Trending Cardiovascular Nutrition Controversies: Part II. J Am Coll Cardiol. 2018 Jul 31;72(5):553-68.
24. Kirthi V, Perumbalath A, Brown E, et al. Prevalence of peripheral neuropathy in pre-diabetes: a systematic review. BMJ Open Diabetes Res Care. 2021 May;9(1).
25. Castelli G, Desai KM, Cantone RE. Peripheral Neuropathy: Evaluation and Differential Diagnosis. Am Fam Physician. 2020 Dec 15;102(12):732-9.
26. Stein J, Geisel J, Obeid R. Association between neuropathy and B-vitamins: A systematic review and meta-analysis. Eur J Neurol. 2021 Jun;28(6):2054-64.
27. Harrington DJ. Laboratory assessment of vitamin B12 status. J Clin Pathol. 2017 Feb;70(2):168-73.
28. Beaudry-Richard A, Abdelhak A, Saloner R, et al. Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous System Injury in Older Adults. Ann Neurol. 2025 Jun;97(6):1190-204.