You may be vitamin B12 deficient and not even know it! Vitamin B12 deficiency is common and underdiagnosed. In the United States, one in five people over age 40 and 6% of people under age 40 are thought to be B12 deficient.1 In most people, B12 deficiency is mild, and therefore the symptoms may be nonspecific.2 Supplementing vitamin B12 or taking vitamin B12 injections, when your body is low on this key nutrient, can restore your energy and provide other health benefits.
In This Article
Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is necessary for red blood cell formation, DNA production, and proper nerve function. Vitamin B12 can come from dietary sources, fortified foods, or supplements. Most vitamin B12 is stored in the liver.
Vitamin B12 is a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase. It helps speed up chemical reactions that are used to form almost one hundred different substrates used in the body, including DNA, RNA, proteins, and lipids. Vitamin B12 helps your body convert nutrients into energy in a form your cells can use.2
A lack of vitamin B12 can cause red blood cells to be overly large and misshapen. Abnormally formed red blood cells cannot move from your bone marrow (where they are produced) to your bloodstream (where they are needed) efficiently, causing megaloblastic anemia. Megaloblastic anemia can cause difficulty breathing, weakness, pale skin color, fatigue, and jaundice (yellow color to the skin or eyes).
When your body does not have enough functional red blood cells, vital organs like the heart, brain, and skeletal muscles may not get enough oxygen. This can cause weakness, brain fog, and fatigue.3
Vitamin B12 deficiency increases homocysteine levels, which has effects throughout the body.4 High homocysteine levels have been linked to an increased risk of heart disease.5 Supplementing with vitamin B12 may help reduce homocysteine.6
Two reviews of scientific studies so far have not found an association between vitamin B12 intake and the risk of heart disease or stroke.2 More research is needed to see if there is a direct link between vitamin B12 deficiency, increased homocysteine, and heart disease.
There may also be a link between elevated homocysteine levels and Alzheimer’s disease and dementia. A combination of low vitamin B12 alone or in combination with low folate concentrations may negatively affect cognitive function.
Clinical trials are needed to better understand the relationship between vitamin B12 and cognitive function, but as of now, according to the National Institute of Health Office of Dietary Supplements, there is no evidence that vitamin B12 supplementation can improve cognitive function, reduce the risk for dementia, or slow the progression of dementia or Alzheimer’s disease.2
Vitamin B12 is essential for optimal nerve function. A lack of vitamin B12 can cause paresthesias, which are sensations of numbness and tingling. Vitamin B12 injections may help reduce pain and paresthesias.7
In one study, patients with severe nerve pain due to the herpes virus experienced relief after a B12 injection.8
Persistently high blood sugar in patients with diabetes can cause paresthesias and nerve pain. Vitamin B12 may reduce these symptoms. More research is needed to determine whether vitamin B12 is an effective treatment for diabetic neuropathy and nerve pain.7
While the link between vitamin B12 supplementation and mood is not fully understood, B12 does play a role in producing serotonin. In an analysis of multiple studies, scientists concluded that short-term B12 use did not improve depressive symptoms. However, long-term use decreased the risk of depression relapse and reduced the risk of developing depressive symptoms.9
More clinical trials are needed to better understand the relationship between vitamin B12, serotonin, and mood.
Vitamin B12 is involved in converting nutrients in food into energy. In an extensive study conducted in the U.S., researchers found an inverse relationship between vitamin B12 deficiency and obesity. Further studies are needed to determine whether it is a causal relationship or whether other variables are involved.10,11
Other vitamins also play an important role in metabolism, so many times vitamin B12 is combined with other nutrients to support weight management, including:
B12 deficiency causes many symptoms, including:
B12 is bound to proteins in foods. Some vitamin B12 is released from foods in the mouth when they are mixed with saliva. After it is released, it binds to haptocorrin, a protein that binds B12 and other cobalamins.
More vitamin B12 is released in the stomach by hydrochloric acid and an enzyme called gastric protease. When B12 is taken as a supplement, it is already in its free form and does not need to be released. Once B12 is in its free form, it binds to intrinsic factor in the stomach and duodenum.
Intrinsic factor is a glycoprotein secreted by specialized cells lining the stomach called parietal cells. The intrinsic factor/vitamin B12 complex is absorbed into the body in the ileum, which is the most distal part of the small intestine. Vitamin B12 then binds to trans-cobalamin, and the complex moves through the bloodstream. The B12/trans-cobalamin complex is then absorbed into your body cells.12 Unfortunately, this multistep process for B12 absorption means that it is much more likely for people to have B12 deficiency than to have deficiencies of more easily absorbed nutrients.
Most people need 2.4 mcg of vitamin B12 per day. Fish, meat, poultry, eggs, dairy products, and fortified cereals are rich in vitamin B12.2
Vitamin B12 deficiency is more common in people with the following conditions:
Vitamin B12 is an essential vitamin that is typically supplied in the diet, as supplements, or by injection. Because of the multi-step absorption process needed to absorb vitamin B12, many people are deficient.
Vitamin B12 supplements may also contain other B-complex vitamins. B12 supplement doses range from 5 to 1,000 mcg. Vitamin B12 must be bound to intrinsic factor to be absorbed. This limits the amount of B12 that can be absorbed from a single supplement dose.
When vitamin B12 supplements contain 1 to 2 mcg of B12, about 50% of it is absorbed. As B12 doses in supplements increase, the percentage absorbed decreases. For example:13
Absorption of B12 by B12 injections is not limited by the carrying capacity of intrinsic factor, so the amount of vitamin B12 available for your body to use after an injection is much higher. For example:13
The effects of a B12 injection may be noticed within about 48 to 72 hours in people who are vitamin B12 deficient. People who are not B12 deficient are unlikely to notice any effects. Each person metabolizes nutrients and vitamins slightly differently, but in most people, B12 injections are metabolized within a week.
Depending on your symptoms and treatment goals, doctors suggest B12 injection frequencies and dosages. Once weekly dosages for four weeks is a common protocol.
If you are vitamin B12 deficient, you will probably notice benefits from vitamin B12 injections within two to three days. For more severe vitamin B12 deficiency, the time to symptom improvement may be longer, with more severe cases taking two to three months to resolve.14
Vitamin B12 is involved in hundreds of chemical reactions, including metabolizing nutrients into energy. Unfortunately, a large proportion of the population is vitamin B12 deficient. There is no international consensus on the lower limits of B12 to define B12 deficiency or how to test for B12 deficiency.
Low vitamin B12 has been linked to an increased risk of cardiovascular disease, metabolic syndrome, obesity, insulin resistance, and abnormal fat metabolism. The link between low vitamin B12 levels and obesity is likely to be due to epigenetic changes in DNA that change metabolism and lead to high insulin levels and fat accumulation.11
Further research is needed to fully understand the effects of vitamin B12 deficiency and the benefits of B12 supplementation.
Start a treatment plan with Lipo B12 injections today!
1. Hunt, Harrington D, Robinson S. Vitamin B12 deficiency. BMJ : British Medical Journal. 2014;349:g5226. doi:10.1136/bmj.g5226
2. National Institute of Health Office of Dietary Supplements. Vitamin B12. Accessed August 2, 2022. https://ods.od.nih.gov/factsheets/vitaminb12-healthprofessional/
3. Rodriguez NM, Shackelford K. Pernicious Anemia. StatPearls. StatPearls Publishing Copyright © 2022, StatPearls Publishing LLC.; 2022.
4. Clarke R, Refsum H, Birks J, et al. Screening for vitamin B-12 and folate deficiency in older persons. The American Journal of Clinical Nutrition. 2003;77(5):1241-1247. doi:10.1093/ajcn/77.5.1241
5. Liu C, Yang Y, Peng D, Chen L, Luo J. Hyperhomocysteinemia as a metabolic disorder parameter is independently associated with the severity of coronary heart disease. Saudi Med J. Jul 2015;36(7):839-46. doi:10.15537/smj.2015.7.11453
6. Robertson J, Iemolo F, Stabler SP, Allen RH, Spence JD. Vitamin B12, homocysteine and carotid plaque in the era of folic acid fortification of enriched cereal grain products. Cmaj. Jun 7 2005;172(12):1569-73. doi:10.1503/cmaj.045055
7. Sun Y, Lai MS, Lu CJ. Effectiveness of vitamin B12 on diabetic neuropathy: systematic review of clinical controlled trials. Acta Neurol Taiwan. Jun 2005;14(2):48-54.
8. Xu G, Lv ZW, Feng Y, Tang WZ, Xu GX. A single-center randomized controlled trial of local methylcobalamin injection for subacute herpetic neuralgia. Pain Med. Jun 2013;14(6):884-94. doi:10.1111/pme.12081
9. Almeida OP, Ford AH, Flicker L. Systematic review and meta-analysis of randomized placebo-controlled trials of folate and vitamin B12 for depression. Int Psychogeriatr. May 2015;27(5):727-37. doi:10.1017/s1041610215000046
10. Sun Y, Sun M, Liu B, et al. Inverse Association Between Serum Vitamin B12 Concentration and Obesity Among Adults in the United States. Front Endocrinol (Lausanne). 2019;10:414. doi:10.3389/fendo.2019.00414
11. Boachie J, Adaikalakoteswari A, Samavat J, Saravanan P. Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies. Nutrients. Jun 29 2020;12(7)doi:10.3390/nu12071925
12. Allen LH, Miller JW, de Groot L, et al. Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review. J Nutr. Dec 1 2018;148(suppl_4):1995s-2027s. doi:10.1093/jn/nxy201
13. Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood. Sep 15 2008;112(6):2214-21. doi:10.1182/blood-2008-03-040253
14. Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. Sep 15 2017;96(6):384-389.