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Understanding Vitamin B12 and Its Role in Metabolism

Don't let a B12 deficiency steal your energy. Explore how this essential vitamin fuels your metabolism for overall well-being.

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By Christina Manian
Jovan Mijailovic
Edited by Jovan Mijailovic

Published June 20, 2024.

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Crash diets, endless gym sessions, and the struggle for a faster metabolism feel like a never-ending cycle. We chase the latest weight loss trends, bombarded with miracle cures and conflicting information.

» Struggling to lose weight? Learn how hormones might be impacting your weight loss efforts.

Vitamin B12 has become a hot topic, with claims that it can supercharge your metabolism and melt fat. But is it actually the missing piece of the weight loss puzzle?

» Optimize your metabolism with a personalized blood analysis. from InsideTracker that looks into your vitamin B12 levels.

Vitamin B12: An essential factor of cellular metabolism

Vitamin B12 plays a vital role in how our bodies produce energy and build critical cellular components. [1] It converts a form called succinyl CoA, which is essential for the citric acid that powers our cells by creating the energy they need to function.

When it comes to breaking down fats for energy, vitamin B12 acts as a helper molecule called a cofactor or coenzyme. It supports the enzyme called methyl malonyl CoA mutase, which regulates how the system transports long-chain fatty acids into the mitochondria. This process is crucial because that's where they turn into energy through cellular respiration.

» Replenish your energy and recover faster after your workouts. Learn what to eat to optimize your post-workout nutrition.

Vitamin B12 doesn't just help with fat metabolism [2]; it's also involved in how our bodies process carbohydrates. [3] It affects our insulin response, which is how the body regulates blood sugar levels after eating carbs. It's also involved in glycogen storage, keeping glucose for later use as fuel.

» Take control of your blood sugar for a sharper mind and healthier body.

B12 also influences protein metabolism by facilitating the production of an enzyme that regulates homocysteine levels.—an amino acid that is their building block. [4,5]

Note: Elevated homocysteine may lead to increased risks of cardiovascular disease, metabolic syndrome, obesity, or stroke. [6]

Effects of vitamin B12 deficiency

  • Impaired glucose metabolism: Vitamin B12 deficiency causes impaired fatty acid synthesis and adverse effects that could lead to insulin resistance. [7,8]
  • Increased inflammation: Research also shows that it may lead to increased cytokine—a pro-inflammatory agent—production in fat tissue as well. [9]
  • Disrupted protein and fat breakdown: Because B12 plays a crucial role in protein and fat metabolism, as it is required for the creation of certain enzymes, a deficiency would significantly negatively impact the process. [10]
  • Pernicious anemia: Because vitamin B12 is required to form red blood cells, deficiency over long periods can lead to pernicious anemia, which is an autoimmune condition that inhibits proper intestinal absorption of vitamin B12. [11]

How vitamin B12 helps form our DNA

Beyond carb and fat metabolism, B12 is required to make an enzyme called methionine synthase. It supports vital one-carbon and folate biochemical cycles, which act as factory production lines for synthesizing critical biomolecules. [12]

Through them, it helps form our DNA, amino acids (the building blocks of proteins), and critical lipids like phospholipids that make up cell membranes. [13] It even allows for the creation of energy transport molecules like creatine.

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Vitamin B12 also plays crucial roles in processes related to our cellular replication. [14] It assists enzymes involved in building nucleotides, the molecular letters that make up our DNA code. It also helps control how that DNA gets methylated, which impacts how we express our genes. [15]

Nucleotide synthesis and DNA methylation are vital for accurately replicating our genes when cells divide. They also help our system correctly transcribe DNA into RNA molecules that turn into proteins. Disruptions in these processes can lead to genetic mutations.

» Learn how much DNA really matters for your perfect eating plan.

Ensuring adequate vitamin B12 intake

Given how essential vitamin B12 is for so many critical bodily functions, it's crucial to ensure you get enough. The good news is that supplements are widely available over-the-counter as standalone pills or as part of B-complex formulations. [16]

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For those looking to get B12 through food sources, some great options are animal products like poultry, red meat, fish, eggs, and dairy. But there are also decent plant-based sources like lentils, beans, seeds, nuts, tofu, and nutritional yeast.

» Learn about one dietitian's experience with vegan keto.

Getting enough vitamin B12 into your body involves more than just altering your diet. There's also one more critical step. To properly absorb B12 from your diet, your stomach needs to produce a special protein called intrinsic factor. It essentially helps shuttle the B12 from your digestive system into your bloodstream.

But, chronic ulcers, stomach parts removed during weight-loss surgery, pernicious anemia, or even some genetic factors can disrupt it. [17] When intrinsic factors are lacking, your body can't absorb B12 properly, no matter how much you consume, causing a deficiency. [18]

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Note: For most adults over age 14, the recommended daily amount of B12 to meet all its vital roles is 2.4 micrograms. [16] Hitting this target maximizes your chances of avoiding deficiency and its adverse impacts on metabolism.

Our verdict on B12: A partner, not a solution

While B12 plays a vital role in metabolism, it's not a magic bullet for weight loss. A balanced diet, regular exercise, and a healthy lifestyle remain the cornerstones of sustainable weight management.

But, ensuring adequate B12 intake can support your body's natural metabolic processes and contribute to overall health and well-being. If you suspect a deficiency, consult a doctor to determine the best course of action.

So, ditch the quick fixes and focus on building a healthy relationship with food and your body. By prioritizing a balanced approach, you can unlock your body's natural potential for a healthy metabolism.

» Unlock your metabolic potential! Get personalized insights and data-driven plans to optimize vitamin B12 with InsideTracker's Ultimate plan


[1] M. Botlagunta, “Nutraceuticals-loaded chitosan nanoparticles for chemoprevention and cancer fatigue,” in Elsevier eBooks, 2016, pp. 783–839. doi: 10.1016/b978-0-12-804305-9.00020-8. Available:

[2] A. Khaire, R. Rathod, A. Kale, and S. Joshi, “Vitamin B12 and omega-3 fatty acids together regulate lipid metabolism in Wistar rats,” Prostaglandins, Leukotrienes and Essential Fatty Acids/Prostaglandins, Leukotrienes, and Essential Fatty Acids, vol. 99, pp. 7–17, Aug. 2015, doi: 10.1016/j.plefa.2015.04.006. Available:

[3] J. Boachie, A. Adaikalakoteswari, J. Samavat, and P. Saravanan, “Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies,” Nutrients, vol. 12, no. 7, p. 1925, Jun. 2020, doi: 10.3390/nu12071925. Available:

[4] J. I. Toohey, “Vitamin B12and methionine synthesis: A critical review. Is nature’s most beautiful cofactor misunderstood?,” BioFactors, vol. 26, no. 1, pp. 45–57, Jan. 2006, doi: 10.1002/biof.5520260105. Available:

[5] B. Shane, “Folate and vitamin B12 function,” in Elsevier eBooks, 2013, pp. 324–328. doi: 10.1016/b978-0-12-378630-2.00039-6. Available:

[6] H. Refsum, P. M. Ueland, O. Nygård, and S. E. Vollset, “Homocysteine and cardiovascular disease,” Annual Review of Medicine, vol. 49, no. 1, pp. 31–62, Feb. 1998, doi: 10.1146/ Available:

[7] A. Ankar and A. Kumar, “Vitamin B12 deficiency,” StatPearls - NCBI Bookshelf, Oct. 22, 2022. Available:

[8] E. Neal, V. Kumar, K. Borges, and J. S. Cuffe, “Vitamin B12 deficiency induces glucose intolerance, delays peak insulin levels and promotes ketogenesis in female rats,” Journal of Endocrinology/Journal of Endocrinology, Dec. 2022, doi: 10.1530/joe-22-0158. Available:

[9] J. Samavat, A. Adaikalakoteswari, J. Boachie, and P. Saravanan, “Increased pro-inflammatory cytokine production in vitamin B12 deficient adipocytes,” Endocrine Abstracts, Nov. 2018, doi: 10.1530/endoabs.59.p158. Available:

[10] A. R. Mathew et al., “Vitamin B12 Deficiency and the Nervous System: Beyond Metabolic Decompensation—Comparing Biological Models and Gaining New Insights into Molecular and Cellular Mechanisms,” International Journal of Molecular Sciences, vol. 25, no. 1, p. 590, Jan. 2024, doi: 10.3390/ijms25010590. Available:

[11] G. Esposito, L. Dottori, G. Pivetta, I. Ligato, E. Dilaghi, and E. Lahner, “Pernicious anemia: the hematological presentation of a multifaceted disorder caused by cobalamin deficiency,” Nutrients, vol. 14, no. 8, p. 1672, Apr. 2022, doi: 10.3390/nu14081672. Available:

[12] A. G. Maynard, B. Petrova, and N. Kanarek, “Notes from the 2022 Folate, Vitamin B12, and One-Carbon Metabolism Conference,” Metabolites, vol. 13, no. 4, p. 486, Mar. 2023, doi: 10.3390/metabo13040486. Available:

[13] C. E. Clare, A. H. Brassington, W. Y. Kwong, and K. D. Sinclair, “One-Carbon Metabolism: linking nutritional biochemistry to epigenetic programming of Long-Term development,” Annual Review of Animal Biosciences, vol. 7, no. 1, pp. 263–287, Feb. 2019, doi: 10.1146/annurev-animal-020518-115206. Available:

[14] K. Halczuk, J. Kaźmierczak-Barańska, B. T. Karwowski, A. Karmańska, and M. Cieślak, “Vitamin B12—Multifaceted in vivo functions and in vitro applications,” Nutrients, vol. 15, no. 12, p. 2734, Jun. 2023, doi: 10.3390/nu15122734. Available:

[15] Z. Rzepka et al., “Response of human glioblastoma cells to vitamin B12 deficiency: a study using the Non-Toxic Cobalamin antagonist,” Biology, vol. 10, no. 1, p. 69, Jan. 2021, doi: 10.3390/biology10010069. Available:

[16] “Office of Dietary Supplements - Vitamin B12.” Available:

[17] J.-L. Guéant, R.-M. Guéant-Rodriguez, and D. H. Alpers, “Vitamin B12 absorption and malabsorption,” in Vitamins and hormones, 2022, pp. 241–274. doi: 10.1016/bs.vh.2022.01.016. Available:

[18] R. Green, “Vitamin B12 deficiency from the perspective of a practicing hematologist,” Blood, vol. 129, no. 19, pp. 2603–2611, May 2017, doi: 10.1182/blood-2016-10-569186. Available: