Amazing Benefits Of B12 Injections

May 16, 2024
Vitamin B12 benefits

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.

What Do B12 Injections Do For You? 

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

Helps Produce Healthy Red Blood Cells

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

A pale, tired girl

May Reduce Homocysteine And Heart Disease

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.

May Improve Cognitive Function And Reduce Dementia

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

May Reduce Pain

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 

May Improve Mood

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. 

Amazing Benefits Of B12 Injections

May Help With Weight Loss

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:

  • Methionine: protects cells from damage and supports the liver when metabolizing fats.
  • Choline: plays an important role in memory and brain function and helps reduce homocysteine levels. 
  • Inositol: is important in cell structure, metabolism, fat burning, energy storage, energy consumption, and the stress response. 
  • L-carnitine: is critical in facilitating fatty acid transport into the mitochondria, where fats are burned for energy. 

Collectively, these lipotropic nutrients can work together to help your body efficiently metabolize fat, which can help with weight loss.

What Are The Symptoms Of B12 Deficiency?

B12 deficiency causes many symptoms, including: 

Neurologic Symptoms 

  • Ringing in the ears
  • Tremors or an involuntary shaking of muscles
  • Numbness and tingling in the arms and legs
  • Confusion
  • Memory problems
  • Muscle weakness
  • Unsteady gait
  • Difficulty in maintaining balance
  • Dizziness
  • A feeling that you need to move your legs at night
  • Vision, taste, or smell disturbances

Neuropsychiatric Symptoms 

  • Psychosis
  • Hallucinations
  • Depression
  • Mania
  • Anxiety
  • Irritability
  • Sleep disturbances

Other Symptoms

  • Insomnia
  • Weakened bones and fractures
  • Abnormal heart rhythms
  • Infertility
  • Weight loss
  • Stomach pain
  • Constipation
  • Appetite loss
  • Soreness of the mouth or tongue 
  • Anemia

Why Do People Become B12 Deficient? 

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: 

  • Lack of intrinsic factor: Intrinsic factor is needed to absorb vitamin B12 into the body. A lack of intrinsic factor causes a type of megaloblastic anemia called pernicious anemia.  
  • Malabsorption: Inflammatory bowel diseases such as Crohn’s disease thicken or damage the intestinal lining and can limit B12 absorption from the gut. 
  • Medication use: Some medications, such as prolonged metformin or proton pump inhibitors, can cause B12 deficiency. 
  • Older adults: Many older adults do not produce enough hydrochloric acid in their stomachs to detach vitamin B12 from dietary proteins. 
  • Inadequate intake: older adults, vegans and vegetarians, and people who consume alcohol in excess may not consume enough vitamin B12-rich foods in their diet. 
Vitamin B12 sign

Why Is B12 Given By Injection? 

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 

  • Only about 2% of a 500-mcg dose of oral vitamin B12 is absorbed.
  • Only about 1.3% of a 1,000-mcg dose of vitamin B12 is absorbed.

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 

  • About 97% of a 10 mcg B12 injection is retained. 
  • About 55% of a 100 mcg B12 injection is retained.
  • About 15% of a 1,000 mcg B12 injection is retained.

How Long Does A B12 Injection Last? 

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. Weekly injections for four weeks are a common protocol. 

How Soon Do You Feel The Benefits Of B12 Injections? 

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. 


Exploring the benefits of B12 injections offers a promising avenue for enhancing health, from boosting energy and metabolism to supporting nerve function and mood improvement. If you’re looking to buy Vitamin B12, considering injections as a method of delivery can provide a more immediate and efficient uptake of this essential nutrient. To understand more about the remarkable advantages of B12 injections for your health and well-being, visit Invigor Medical for detailed information and options.

Frequently Asked Questions

What are the positive effects of B12 injections?

B12 injections can provide several potential benefits, including increased energy levels, improved mood, enhanced cognitive function, better sleep quality, and relief from symptoms associated with B12 deficiency, such as fatigue, weakness, and anemia.

Why do I feel better after a B12 injection?

Many people report feeling better after a B12 injection because it helps address B12 deficiency, which can lead to various health issues. The improvement in energy and mood is often attributed to the correction of this deficiency.

How soon do you feel the benefit of B12 injections?

The time it takes to feel the benefits of B12 injections can vary among individuals. Some people may experience improvements in energy and mood within a few days to a week, while others may take longer. It depends on the severity of the deficiency and how quickly your body responds to the treatment.

Why does B12 make me feel so much better?

B12 is essential for various bodily functions, including the production of red blood cells and the proper functioning of the nervous system. When you have a B12 deficiency, these processes can be impaired, leading to symptoms like fatigue and mood changes. Receiving B12 injections helps restore the necessary levels of this vitamin, which, in turn, can alleviate these symptoms and contribute to an overall sense of well-being.

Author: Leann Poston, M.D.
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