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Vitamin b12


Vitamin B12 injections have become increasingly popular, as observed by the growing number of clinics offering this service. This deficiency is likely underdiagnosed due to lack of obvious symptoms, but current estimates report that about 1.5-15% of the population are deficient in Vitamin B12 1. Clinical symptoms that may present with a deficiency include fatigue and muscle weakness, constipation, loss of appetite, weight loss, megaloblastic anemia, peripheral hypoesthesia, poor balance, poor concentration and memory, and pain in the mouth and tongue, and in infants may present with failure to thrive, motor deficits, delayed development 2. Most individuals with a Vitamin B12 deficiency have subclinical symptoms 2, and would need diagnostic lab testing to determine if they are deficient.

The recommended daily intakes of Vitamin B12 in each life stage are as follows 1:

Birth to 6 months-0.4 mcg

Infants 7–12 months-0.5 mcg

Children 1–3 years-0.9 mcg

Children 4–8 years-1.2 mcg

Children 9–13 years-1.8 mcg

Teens 14–18 years-2.4 mcg

Adults-2.4 mcg

Pregnant teens and women-2.6 mcg

Breastfeeding teens and women-2.8 mcg

The practice of Vitamin B12 injection is likely associated with growing awareness of the prevalence of Vitamin B12 deficiency. Its absorption decreases with age especially due to the declining hydrochloric acid levels in the stomach, which is required to release Vitamin B12 from food. There are also other conditions that may further increase the risk of Vitamin B12 absorption such as pernicious anemia, gastric resection, ileocecal resection, celiac disease, or Crohn's disease. Different conditions can interfere by reducing the amount of hydrochloric acid (stomach acid), pancreatic enzymes, intrinsic factor (required for absorption of B12), or a disruption at the site of absorption at the terminal ileum (junction of the small and large intestine). Individuals with conditions such as these, will absorb only about 1-2% of Vitamin B12 obtained through diet and oral supplementation through passive diffusion 3. Vitamin B12 is also only naturally found in animal products such as beef, poultry, fish, eggs, and dairy products, or in fortified foods such as cereal or juice 2, and in cases where individuals do not consume animal products, or in low amounts, there is a greater risk of deficiency.

Although Vitamin B12 injections are increasingly popular, there is preliminary evidence showing that large doses of oral Vitamin B12 of 2,000 mcg per day is more effective than daily injections 4, 3. Opting for oral intake of Vitamin B12 as a supplement may be a better alternative for a number of reasons, which include barriers to traveling to a clinic such as those with disabilities or older individuals for whom commuting is more difficult, individuals that may be on anti-coagulant therapies, cost saving from injection over supplements, and the possible discomfort of the injection 4 5.

Another reason I see individuals opting to receive Vitamin B12 injections is for an energy and metabolism boost. It is being advertised to help increase energy levels and increase weight loss. This is a claim for which there is little evidence. Vitamin B12 does play an important role in the formation of red blood cells that carry oxygen throughout the body, DNA synthesis, neurological function, as well as supporting enzymatic process of fat and protein metabolism. Due to its role in the many different processes within the body, a deficiency will manifest in symptoms as stated earlier, which include fatigue and muscle weakness. If an individual is chronically deficient they may begin to think that state of fatigue and weakness is normal, and having a B12 injection that normalizes their body is seen as a boost.

Is this bad? No. It means at the very least they are addressing a nutritional deficiency, but I do want to clarify what’s going on deeper within the body. Individuals may opt to receive Vitamin B12 for boosting their energy and metabolism, and it may also aid in the reduction of subclinical Vitamin B12 deficiencies 6. If an individual experiences these benefits with a Vitamin B12 injection, they may want to consider receiving diagnostic testing to determine if they are deficient, and the reason why they are deficient. Once they identify a cause, then a proper plan can be set into motion to prevent becoming deficient in the future. This may very well be Vitamin B12 injections, or possibly oral supplementation, or even the reduction of antacid intake.

To conclude, based on currently available scientific evidence, receiving Vitamin B12 injections may not be the most cost effective option, and oral supplementation in higher doses may be as effective as injections, but the research is preliminary. I would first recommend diagnostic labs for individuals that are concerned with their energy levels, and also if they fall into categories of risk for Vitamin B12 deficiency. Cases of deficiency may be addressed in the early stages with high dose supplements and possibly followed up with a recommendation for injection therapy.


1. Vitamin B12 - Consumer. National Institutes of Health. June 24, 2011. https://ods.od.nih.gov/factsheets/vitaminb12-consumer/. Accessed July 11, 2015.

2. CDC - History, Vitamin B12 Deficiency - NCBDDD. Centers for Disease Control. June 29, 2009. http://www.cdc.gov/ncbddd/b12/history.html. Accessed July 11, 2015.

3. Butler CC, Vidal-Alaball J, Cannings-John R, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency: a systematic review of randomized controlled trials. Family Practice. March 2006:279-285.

4. Shatsky M. Evidence for the Use of Intramuscular Injections in Outpatient Practice. American Family Physician. 2009;4:297-300.

5. Sanz-Cuesta T. Oral versus intramuscular administration of vitamin B12 for the treatment of patients with vitamin B12 deficiency: a pragmatic, randomised, multicentre, non-inferiority clinical trial undertaken in the primary healthcare setting. Public Health. 2012;12:1-11.

6. Environmental Nutrition. B Vitamin-Laced Drinks Not Likely to Be Beneficial for an Energy Boost. Environmental Nutrition. April 2009:7.