Vitamin B12 Deficiency – Sources, Causes, Symptoms, Dose

Vitamin B12 deficiency is estimated to affect between 300,000 to 3 million Americans but the exact prevalence is not known. It is believed that it may be much more common. The body sources vitamin B12 from meat and dairy and usually has sufficient stores to last a few years. However, in the elderly who are not maintaining proper nutrition and with vegans, there is a greater risk of vitamin B12 deficiency arising.

What is vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble vitamin that has a host of important roles in the human body. Therefore vitamin B12 deficiencies do not arise suddenly but are associated with a long term low vitamin B12 intake and certain chronic diseases. Depending on the severity and duration of the deficiency, insufficient vitamin B12 can affect the blood, nerves and mental health.

Supplementation of vitamin B12 is usually not necessary in people who eat a balanced diet containing animal protein. However, when a deficiency arises then oral supplementation (pills) or parenteral supplementation (injections) are necessary. A vitamin B12 deficiency can lead to serious complications and even increase the risk of certain deadly conditions. Ideally a deficiency should be prevented through dietary means.

Read more on vitamin deficiencies.

Foods High in Vitamin B12

Vitamin B12 is abundant in most animal proten. For example 2 cups of low-fat milk has sufficient vitamin B12 to meet the recommended dietary amount (RDA) for people aged 14 years and older. In addition, most breakfast cereals are fortified with sufficient vitamin B12 in just 1 serving. Therefore a breakfast of milk with fortified breakfast cereal provides more than the required dietary amount (RDA) for the day.

  • Red meat (beef, pork, lamb) including offals.
  • Poultry and eggs.
  • Milk and yogurt.
  • Fish (freshwater and saltwater) and other seafoods.

Red meat liver and clams are high in vitamin B12. Since the liver can store vitamin B12 for long periods of time, these foods do not have to be eaten daily. Occasional consumption will be sufficient to prevent a deficiency and even treat a mild deficiency provided that there are no complicating factors.

Required Dose

Most people who eat meat and/or dairy should derive sufficient vitamin B12 from a balanced diet.  The recommended dietary amounts (RDA) of vitamin B12 varies by age and physiologic state:

  • 0–6 months = 0.4 mcg
  • 7–12 months = 0.5 mcg
  • 1–3 years = 0.9 mcg
  • 4–8 years = 1.2 mcg
  • 9–13 years = 1.8 mcg
  • 14 years or older = 2.4 mcg
  • Pregnant females = 2.6 mcg
  • Breastfeeding mothers = 2.8 mcg

* mcg =micrograms

People over the age of 50 years may require supplementation with higher doses of vitamin B12. This has been discussed below under Supplementation.

Causes of B12 Deficiency

There are two main reasons for vitamin B12 deficiency – nutritional deficiencies and malabsorption syndromes. However, there are various chronic conditions that can also contribute to vitamin B12 deficieny.

Nutritional Deficiencies

Insufficient intake of dietary vitamin B12 is mainly seen in the elderly and vegans. Vitamin B12 is derived from animal protein – either by consuming meat and/or dairy. The elderly who are not consuming a balanced diet may therefore be at risk. One of the reasons is the “tea and toast” diet that some elderly people follow for a host of reasons, including difficulty preparing meals, diminished appetite, impairment with chewing or swallowing and financial restrictions. Vegans abstain from all animal protein, including diary.

Malabsorption Syndromes

For vitamin B12 to be absorbed in the gut, there has to a protein known as intrinsic factor present. It is secreted by the parietal cells in the stomach lining. In certain conditions like pernicious anemia these cells are damaged due to an autoimmune response. As a result there is a vitamin B12 deficiency. Drugs used for gastritis and peptic ulcers, such as proton pump inhibitors (PPIs) and H2-blockers, may also affect vitamin B12 absorption. It is more likely to arise in people who use these drugs for a long period.

Other Causes

  • Alcoholism
  • Atrophic gastritis
  • Bariatric surgery
  • Celiac disease
  • Chronic diarrhea
  • Crohn’s disease
  • Intestinal parasitic worms (helminths) infestation
  • Small intestine bacterial overgrowth (SIBO)
  • Whipple’s disease
  • Zollinger-Ellison syndrome

Symptoms of Vitamin B12 Deficiency

Vitamin B12 deficiency causes a host of different conditions. Therefore the signs and symptoms may be diverse. Some of the signs and symptoms that may be seen with a vitamin B12 deficiency includes:

  • Fatigue
  • Weakness
  • Dizziness
  • Palpitations
  • Shortness of breath
  • Tingling and numbness
  • Paleness (pallor)
  • Alterations in bowel habit such as constipation or diarrhea
  • Poor vision
  • Depression
  • Impaired memory

Conditions caused by vitamin B12 deficiency

A vitamin B12 deficiency is more likely to affect the following systems and give rise to these conditions. Multiple factors determine which of these conditions will arise, including the severity and duraton of the deficiency.

  • Blood
    – Leukopenia
    – Megaloblastic anemia
    – Thrombocytopenia
  • Nervous system
    – Paresthesias (tingling, numbness)
    – Peripheral neuropathy
  • Mental health
    – Dementia
    – Depression
    – Irritability
    – Memory impairment
    – Psychosis

Vitamin B12 deficiency can also increase the risk of cardiovascular diseases such as a heart attack or stroke.

Vitamin B12 Supplementation

There are two options for vitamin B12 supplementation – oral (in the form of pills) or parenteral (intramuscular injections). Contrary to popular belief, oral supplementation is as effective as parenteral supplementation. However, absorption of the vitamin B12 in the gut may be impaired to some degree in malabsorption syndromes and intramuscular injections may be the preferred option.

Oral Supplementation

Always speak to a medical professional before commencing with oral vitamin B12 supplementation.

  • Initial dose = 1,000 mcg to 2,000 mcg daily for 1 to 2 weeks
  • Maintenance dose = 1,000 mcg daily for life

The above doses are for people who have been diagnosed with a vitamin B12 deficiency, especially if one or more conditions related to the deficiency has arisen. People older than 50 years may need to constantly supplement vitamin B12 with doses of 25 to 100 mcg to prevent deficiencies.

Parenteral Supplementation

Intramuscular injections of vitamin B12 should be done by a medical professional.

  • Initial dose = 100 to 1,000 mcg daily/every second day for 1 to 2 weeks
  • Maintenance dose = 100 to 1,000 mcg every 1 to 3 months

It is important to note that supplementation may not always immediately reverse every condition that arises as a complication of vitamin B12 deficiency. Prevention of a deficiency with sufficient dietary intake of vitamin B12 is always the better option.



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