How Long Does It Take for Vitamin B12 to Work?

Many factors determine how quickly a vitamin B12 supplement will work. However, you can optimize the effectiveness of your vitamin B12 supplementation for fast, effective results by understanding some key factors such as digestion, deficiency, and different types of supplements.

Keep reading to learn more about:

• What is vitamin B12?
• The steps required for vitamin B12 absorption
• Dietary recommendations
• Vitamin B12 deficiency
• Risk factors for deficiency
• Vitamin B12 food sources and supplements
• Supplemental forms and delivery of B12 supplements
• Why choosing a sublingual option makes sense

What is Vitamin B12?

Vitamin B12 is an essential vitamin that you obtain from your diet. Vitamin B12 is unique in that it is a large molecule that contains the mineral cobalt; hence vitamin B12 is known as cobalamin. (Source 1)

Like vitamin C and other B vitamins, vitamin B12 is a water-soluble vitamin. Water-soluble vitamins aren’t readily stored in the body and require frequent replenishment through the diet.

Vitamin B12 is the cofactor required for two critical enzymes found in every cell of the body. These enzymes are:

1. Methionine synthase – a key regulator of the methylation cycle. Along with folate, the methylation cycle requires vitamin B12 to keep the cycle turning, regenerating methionine from homocysteine and synthesis of methyl donors. For a complete breakdown of this cycle, read The Methylation Cycle and Active Methyl B12 and Methyl Folate.

2. L-methymalonyl-coenzyme A mutase – a key enzyme in the citric acid cycle, which turns macronutrients from food into energy as ATP. To learn more about the citric acid cycle, read Advantages of Taking Liposomal Multivitamins with Minerals, which dives into all the micronutrients required for energy metabolism. (Source 2)

Because these enzymes require B12 to function, vitamin B12 is critical for:

• Neurotransmitter synthesis
• Brain health
• Heart health
• Nervous system health
• Immune system health
• Red blood cell production
• Energy levels
• Overall health (Source 2)

Vitamin B12 Absorption

Vitamin B12 requires some extra steps in the digestion process for optimal absorption compared to other nutrients. A well-functioning gastrointestinal system becomes critical for this nutrient to make its way into the body. (Source 1, 2)

Here are the vitamin B12 digestion and absorption steps:

1. In the stomach – Stomach acid and enzymes release vitamin B12 from animal foods. Vitamin B12 binds to R-protein produced by stomach cells.

2. In the upper small intestine – R-protein breaks down with the change of pH and pancreatic enzymes. B12 then binds to an intrinsic factor (also produced by stomach cells).

3. In the lower small intestine (ileum) – The vitamin-B12-intrinsic factor complex is absorbed into the enterocyte (cell lining intestine) with the help of calcium.

4. In the enterocyte – B12 releases from intrinsic factor and is either used by the cell or sent into circulation to be used by another cell in the body. (Source 1, 2)

Vitamin B12 Recommendations

The recommended dietary allowance (RDA) for vitamin B12 is 2.4 micrograms (mcg) per day for adults. Daily needs increase to 2.6 micrograms per day for pregnant women and 2.8 mcg per day for breastfeeding women. Only about half of this intake is absorbed. (Source 2, 3)

Because of the elaborate absorption process, the body only absorbs as much B12 as it can handle, which is why you’ll see dietary supplements containing higher doses than those naturally obtained from food.

Vitamin B12 Deficiency

Blood work is used to diagnose vitamin B12 deficiency. Low levels of serum vitamin B12 and elevated methylmalonic acid (MMA), a B12 metabolite, signify clinical deficiency. However, patients will often have blood levels within the lab range while still displaying symptoms of vitamin deficiency. (Source 4)

This type of subclinical deficiency is likely even more widespread than severe cases. (Source 1)

The classic presentation of vitamin B12 deficiency is megaloblastic anemia, where red blood cells are big and inefficient at carrying oxygen. This anemia develops because of the impaired methylation cycle during blood cell formation. (Source 4)

However, deficiency may present differently for each person. Symptoms of vitamin B12 deficiency include:

• Fatigue
• Depression
• Elevated homocysteine, a risk factor for heart disease
• Cognitive impairment, memory loss, dementia
• Impaired walking ability
• Numbness and tingling of hands and feet
• Osteoporosis
• Infertility or miscarriage
• Neural tube defects (Source 2)

In some cases, neurological symptoms may become permanent, even when the vitamin B12 deficiency is corrected because vitamin B12 is required to maintain the myelin sheath of nerve cells. (Source 1)

Who’s at Risk? Vitamin B12 Deficiency Causes

• Age. Because of impaired absorption, older adults are at increased risk for vitamin B12 deficiency. However, older adults may also eat less vitamin B12, use more medications, have higher rates of gastritis, and other factors contributing to deficiency rates. (Source 2)

How to Improve Vitamin B12 Levels with Diet and Supplements

Let’s dive into diet and supplementation strategies to replete or maintain vitamin B12 levels.

The first step is to include vitamin B12 food sources in the diet daily. Food sources include shellfish, meat, fish, poultry, eggs, and dairy products. You’ll also find vitamin B12-fortified foods like cereals, bars, and protein powders. If you don’t eat many of these foods (or any at all), you’ll need a daily B12 supplement or multivitamin.

While working on the diet piece, consider supplementation. Both the form of vitamin B12 and the method of delivery are important.

Types of Vitamin B12 Supplements

Most vitamin B12 supplements on the market are cyanocobalamin, an inexpensive, synthetic form of vitamin B12. Cyanocobalamin requires conversion to adenosylcobalamin (adenosyl B12) and methylcobalamin (methyl B12), the active cofactor forms of this nutrient. Unfortunately, many people have poor conversion rates, especially if they have certain genetic polymorphisms.

Directly taking adenosyl B12 and methyl B12 is preferred because cells can immediately use vitamin B12. (Source 7)

Read more about the forms of vitamin B12 and why active forms are preferred here.

Side effects to vitamin B12 supplements are uncommon as excess vitamin B12 is not stored and excreted via the urine. However, some people will tolerate certain forms of vitamin B12 and folate better than others because of genetics and other factors, so be sure to work with your functional medicine healthcare provider for guidance.

Methods of Vitamin B12 Supplementation and Effectiveness

In addition to the form of vitamin B12, the delivery method will determine how quickly and effectively supplementation works.

Oral supplements must make their way through all the steps in the stomach and intestines required for absorption, which may not be optimal for some people. If the gastrointestinal system is working well, some evidence suggests it takes three to four hours for oral vitamin B12 to make its way into circulation. (Source 1)

In many cases, it makes sense to bypass the GI tract altogether by using vitamin B12 injections or sublingual supplements.

Vitamin B12 shots work very quickly to increase blood levels of vitamin B12. Many patients report an immediate sense of increased energy. It may take a week or so to see improvements in red blood cells and other symptoms.

The downside to vitamin B12 injections is cost and accessibility. However, sublingual vitamin B12 also bypasses the gastrointestinal system as it’s absorbed under the tongue directly into circulation and is immediately available to cells. In addition, it’s effective at addressing vitamin B12 deficiency and maintaining healthy levels. 

CoreMed Science Active B12 + Folate Lozenge utilizes a sublingual delivery system. It provides the active forms of vitamin B12 and folate (methylfolate, not folic acid), making it a great alternative to oral vitamin B12 supplements. The combination of vitamin B12 and folate provides optimal support for methylation and red blood cell production.

So, how fast will vitamin B12 supplements work? It depends on

• If you are vitamin B12 deficient and the extent of the deficiency
• Dietary sources of vitamin B12
• Digestive system function
• The form of vitamin B12 supplementation
• The method of supplement delivery

Taking sublingual active vitamin B12 is the most available, affordable, and effective way to improve vitamin B12 levels, prevent deficiency symptoms, and support overall well-being.

References

1. Allen, L. H., Miller, J. W., de Groot, L., Rosenberg, I. H., Smith, A. D., Refsum, H., & Raiten, D. J. (2018). Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review. The Journal of nutrition, 148(suppl_4), 1995S–2027S. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6297555/
2. Linus Pauling Institute Micronutrient Information Center. Vitamin B12. Accessed February 2, 2023. Full text: https://lpi.oregonstate.edu/mic/vitamins/vitamin-B12
3. Shipton, M. J., & Thachil, J. (2015). Vitamin B12 deficiency - A 21st century perspective . Clinical medicine (London, England), 15(2), 145–150. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4953733/
4. Wolffenbuttel, B. H. R., Wouters, H. J. C. M., Heiner-Fokkema, M. R., & van der Klauw, M. M. (2019). The Many Faces of Cobalamin (Vitamin B12) Deficiency. Mayo Clinic proceedings. Innovations, quality & outcomes, 3(2), 200–214. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6543499/
5. Esposito, G., Dottori, L., Pivetta, G., Ligato, I., Dilaghi, E., & Lahner, E. (2022). Pernicious Anemia: The Hematological Presentation of a Multifaceted Disorder Caused by Cobalamin Deficiency. Nutrients, 14(8), 1672. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9030741/
6. Infante, M., Leoni, M., Caprio, M., & Fabbri, A. (2021). Long-term metformin therapy and vitamin B12 deficiency: An association to bear in mind. World journal of diabetes, 12(7), 916–931. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8311483/
7. Paul, C., & Brady, D. M. (2017). Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integrative medicine (Encinitas, Calif.), 16(1), 42–49. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312744/