How much do you know about Vitamin B12?

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Vitamin B12, one of the eight B vitamins, is vital to the healthy function of every cell in the body. Insufficient vitamin B12 intake – or insufficient absorption in the gastrointestinal system – can cause a wide range of health problems. In addition, some of these can be confused with complications related to diabetes, so it’s important to know the possible causes, signs, and symptoms of deficiency. How much do you know about vitamin B12? Take this quiz and find out!


1. The primary functions of vitamin B12 in the body are the formation of red blood cells and the maintenance of a healthy nervous system.

2. Vitamin B12 is naturally available in which of the following foods? (More than one answer may be correct.)
A. Salmon.
B. Beef.
C. Potatoes.
D. Lettuce.

3. Insufficient amounts of B12 in the body can cause which of the following symptoms? (More than one answer may be correct.)
A. Tingling or numbness in the hands or feet.
B. Diarrhea or constipation.
C. Nausea.
D. Weakness and fatigue.
E. Confusion, memory loss, or dementia.

4. B12 deficiency is a common side effect of long-term treatment with which of the following diabetes drugs?
A. Thiazolidinediones (brand names Actos, Avandia).
B. Metformin (Glucophage, Glucophage XR, Riomet, Fortamet, Glumetza).
C. Sulfonyureas (DiaBeta, Glynase, Micronase, Glucotrol, Glucotrol XL, Amaryl).
D. DPP-4 inhibitors (Januvia, Onglyza).

5.Vitamin B12 supplements can be taken in which of the following ways? (More than one answer may be correct.)
A. By injection.
B. By pill, either swallowed or sublingually (absorbed under the tongue).
C. By nasal spray.
D. In B12-fortified foods, such as certain breakfast cereals.

6. Bodily damage from B12 deficiency can be permanent.


1. TRUE. Vitamin B12, along with related B vitamins B6 and B9 (better known as folic acid), is important in the formation of hemoglobin, the oxygen-carrying component of red blood cells. It also plays a key role in making the fats and proteins that form myelin, the material that covers and insulates the nerves in the brain and spinal cord. Additionally, vitamin B12 has a part in almost a hundred different reactions that govern metabolism and tissue synthesis, growth, and repair. Along with vitamin B6 and folic acid, it also aids in the formation of hormones and neurotransmitters, chemicals that nerve cells use to send signals to each other.

2. A and B. Vitamin B12 is naturally present in all foods of animal origin, including fish, meat, eggs, and dairy products. Vitamin B12 is generally absent in plant-based foods, but many processed foods such as cereal, nutrition bars, and some beverages and snacks are fortified with vitamin B12. The Dietary Reference Intake for men and nonpregnant or lactating women 14 years of age and older is 2.4 micrograms (mcg) per day. Three ounces of baked trout has 14.7 mcg of vitamin B12, a large hard-boiled egg has 0.6 mcg, and an ounce of low-fat Cheddar cheese has 0.2 mcg.

Lettuce and potatoes are not sources of vitamin B12. However, dark leafy lettuces (such as endive, Boston, or Bibb) and potatoes are sources of folic acid, one of the B vitamins that works with vitamin B12 in many of its functions.

3. A, B, D, and E. There are many symptoms of vitamin B12 deficiency. These include fatigue, weakness, poor balance and coordination, loss of appetite, weight loss, soreness of the mouth and tongue, diarrhea or constipation, and numbness, burning, and tingling in the hands and feet, which can be mistaken for diabetic neuropathy. Some of these symptoms occur as a result of anemia caused by vitamin B12 deficiency, but the neurological changes (numbness, tingling, etc.) can occur even in the absence of anemia. Early identification of B12 deficiency and intervention is therefore important. Vitamin B12 deficiency does not cause nausea.

4. B. Metformin – and any combination pill that contains it (such as Metaglip, Actoplus Met, or Avandamet) – can cause vitamin B12 deficiency. How metformin reduces absorption of B12 is not yet clear, but it’s likely related to changes in intestinal mobility, small bowel bacterial overgrowth, and/or changes in B12 absorption by intestinal cells (a process that requires calcium to take place). In some cases, taking calcium supplements improves vitamin B12 absorption.

The longer a person is on metformin or combination drugs that include it, and the higher the dose, the greater the likelihood of developing a vitamin B12 deficiency. Use of prescription or over-the-counter antacid medicines called histamine-2 receptor antagonists (such as Pepcid, Zantac, or Tagamet) or proton pump inhibitors (including Prilosec, Prilosec OTC, and Prevacid) while taking metformin further increases the risk of B12 deficiency. Additionally, certain other health conditions increase the probability of B12 deficiency for various reasons, including diseases of the gastrointestinal tract (such as Crohn disease or ulcerative colitis), gastric bypass surgery, HIV, multiple sclerosis, and some autoimmune diseases. Thiazolidinediones, sulfonylureas, and DPP-4 inhibitors do not cause vitamin B12 deficiency.

5. A, B, C, and D. Everyone should consume a wide variety of either naturally occurring or fortified food sources of vitamin B12, but if supplementation is needed, a person’s symptoms, drug history, and overall health determine the best way to boost his intake. People with clear clinical deficiency and its associated symptoms (especially neurological symptoms), as well as people at high risk of deficiency and those with conditions that make it impossible to absorb enough B12 from the digestive process should receive injections of vitamin B12. Individuals who are asymptomatic but at low or moderate risk for B12 deficiency typically can supplement their intake orally with pills or nasally with a spray or gel. A skin patch is also available.

6. TRUE. The saying “An ounce of prevention is worth a pound of cure” rings true when it comes to vitamin B12 deficiency. Restoration of vitamin B12 levels in the blood resolves the anemia, fatigue, weakness, and gastrointestinal maladies associated with vitamin B12 deficiency, but the neurological and mental symptoms (poor memory, depression, irritability) may be permanent. If the deficiency is identified and treated early enough, these abnormalities typically improve. However, the longer the symptoms have been present and the more intense the symptoms are, the lower the likelihood of reversal.

Originally Published June 6, 2011

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