Key takeaways
- Vitamin B12 shots are injections that a doctor may prescribe to treat a vitamin B12 deficiency. They may be useful for people with gastrointestinal issues, older adults, vegans, and vegetarians.
- A doctor may inject vitamin B12 shots into a person’s muscle every other day for around 2 weeks. If the deficiency is due to an underlying condition, they may require ongoing shots.
- People may not be able to take vitamin B12 shots if they have a history of sensitivity to vitamin B12. In rare cases, these shots can cause adverse side effects, including anaphylaxis.
A vitamin B12 deficiency can lead to various health problems, ranging from fatigue to permanent neurological changes.
Vitamin B12 injections are usually for people with conditions that affect the body absorption of vitamin B12 and those who have undergone gastric surgery. This is because shots enable the body to absorb vitamin B12 without going through the digestive system.
This article addresses the importance of maintaining adequate vitamin B12 levels and outlines the benefits and risks associated with vitamin B12 shots.
Vitamin B12 is an essential water-soluble vitamin that plays a role in many bodily functions,
- DNA production
- red blood cells
- nerve cells
Without vitamin B12, a person may feel tired and weak due to megaloblastic anemia.
Vitamin B12 is present in many dietary sources, such as:
- meat
- fish
- eggs
- dairy products
- nutritional yeast
- some fortified foods
Vitamin B12 shots are a form of supplementation that contains a synthetic version of vitamin B12, or cyanocobalamin. A doctor will inject the shot into the muscle or deep into the skin. If they inject it into a vein, the body may lose a high proportion as the person passes urine.
Cyanocobalamin is available in liquid, tablet, nasal spray, and capsule form. Manufacturers may fortify certain foods, such as cereals, with the synthetic form of vitamin B12.
How long do vitamin B12 shots last?
How often a person will require shots depends on what is causing their B12 deficiency. Initially, a person may need B12 supplementation shots every other day for around 2 weeks or until symptoms improve.
If a person’s B12 deficiency is due to diet, they may not require further shots or only require them once or twice per year.
In cases where a chronic condition is causing a deficiency, people may require B12 shots around every month. People may be able to administer their own injections.
Vitamin B12 shots are only available by prescription following a clinical diagnosis of low levels. However, low levels
Some people’s bodies do not produce enough stomach acid or intrinsic factor if they have a condition known as autoimmune atrophic gastritis. These people may need vitamin B12 shots to reduce their risk of deficiency, which can lead to pernicious anemia.
Other people needing shots include those who have had gastrointestinal surgery if their digestive system cannot absorb vitamin B12 efficiently.
People with symptoms of vitamin B12 deficiency
It is a good idea for anyone with the following signs and symptoms of a vitamin B12 deficiency or pernicious anemia to consult a doctor:
People with gastrointestinal issues
Conditions that affect the gastrointestinal tract may affect vitamin B12 release or absorption, including:
- pernicious anemia, which can lead to gastric atrophy, or damage to the stomach
- fish tapeworm infestation
- bowel or pancreatic cancer
- folic acid deficiency
- overgrowth of bacteria in the small intestine
- diabetes
- thyroid disease
- Crohn’s disease
- celiac disease
- chronic pancreatitis
People who have undergone gastrointestinal surgery, including weight loss, may have fewer cells necessary to secrete stomach acid and intrinsic factor. This can also affect vitamin B12 absorption.
Older adults
Vitamin B12 deficiency is
Vegetarians and vegans
Vitamin B12 mainly occurs in animal foods, so people who follow a plant-based diet have a
In some cases, a doctor may recommend injections, but
Vegetarians or vegans who are pregnant may
If the infant is entirely breastfed, they may not consume enough vitamin B12. This can lead to permanent and severe neurological issues.
To diagnose a vitamin B12 deficiency, doctors
A doctor may order blood tests if they suspect a person has a vitamin B12 deficiency, including a complete blood count and tests to check levels of B12 and folate in the blood.
In some cases, a doctor may refer a person to a specialist, such as:
- a nutritionist or dietitian
- a hematologist, who specializes in treating blood conditions
- a gastroenterologist, who specializes in treating gastrointestinal (GI) conditions
The table below contains the
| Age group | Amount |
|---|---|
| 0 to 6 months | 0.4 micrograms (mcg) |
| 7 to 12 months | 0.5 mcg |
| 1 to 3 years | 0.9 mcg |
| 4 to 8 years | 1.2 mcg |
| 9 to 13 years | 1.8 mcg |
| 14+ years | 2.4 mcg |
| Pregnant adults | 2.6 mcg |
| Breastfeeding adults | 2.8 mcg |
However, a doctor can advise on an individual’s specific needs.
A doctor may recommend vitamin B12 shots for people at risk of a deficiency or its complications, particularly if they are unable to take oral supplements.
Researchers associate a vitamin B12 deficiency with various health issues,
- megaloblastic anemia
- neurological changes and disorders
- infertility
- depression
- neural tube defects and developmental delays in children born to those with a vitamin B12 deficiency
Supplementation may help to reduce the risk of these health issues. A doctor may choose injections over oral supplementation to limit any barriers to absorption.
There is
After having a B12 shot, a person should monitor for adverse symptoms and seek medical help if they experience:
- severe pain at the injection site
- mild diarrhea
- a swelling sensation in the body
- temporary itching of the skin
In rare cases, a person may also be at risk of:
- anaphylaxis
- pulmonary edema
- congestive heart failure
- peripheral vascular thrombosis, which involves blood clots
- polycythemia vera, which is a type of blood cancer
If anyone experiences difficulty breathing, hives, or swelling, they need emergency medical help. They may be experiencing anaphylaxis, which is a severe allergic reaction.
Medications side effects
Vitamin B12
Some other prescription medications can directly cause a vitamin B12 deficiency, such as proton pump inhibitors and metformin.
Allergies and medical conditions
Those with allergies or medical conditions should always inform a doctor before receiving a vitamin B12 shot. Vitamin B12 shots may not be suitable for people with a history of:
- sensitivity to vitamin B12
- Leber’s disease, which affects the optic nerve
- kidney problems
- hypokalemia (low potassium levels)
- deficiencies in other nutrients, particularly folic acid and iron
Vitamin B12 injections typically begin to work straight away. However, it may take a number of days or weeks before a person notices improvements in their symptoms.
Precautions a person may need to take after receiving a B12 injection may depend on which side effects they experience. For example, if they experience dizziness, they should avoid driving.
A person’s doctor can provide them with information about any specific activities they may need to avoid or any other considerations. This might include limiting alcohol intake.
Most people get enough vitamin B12 from their diet, but some people have a deficiency. This can be due to having low levels of intrinsic factor in the digestive system, having a digestive condition, or following a plant-based diet.
If dietary sources are insufficient, however, a doctor may recommend supplementation through pills or injections, depending on the cause of the deficiency.