Supplement Spotlight: Vitamin B12

Vitamin B12 is an essential nutrient required for good health.

B12 deficiency, a common condition throughout the world that can lead to serious outcomes like anemia and neurological problems, can be avoided with the right approach. By learning about various B12 sources, you can achieve the recommended daily intake (1).

This article helps you decide the best approach for reaching your B12 needs.

What is Vitamin B12?

Vitamin B12, also known as cyanocobalamin or methylcobalamin, is an essential, water-soluble vitamin.

It’s found in various animal-based foods as well as fortified in foods and nutritional supplements.

This vitamin primarily acts as an enzyme cofactor, helping with DNA and energy production.  Also, B12 is necessary for proper red blood cell (RBC) formation, neurological function, and protein and fat metabolism.

Vitamin B12 Deficiency

Deficient B12 levels cause a range of health problems.

B12 deficiency symptoms include:

  • Megaloblastic anemia
  • Fatigue and weakness
  • Constipation
  • Loss of appetite and weight loss
  • Numbness and tingling in hands and feet
  • Poor balance
  • Poor memory and dementia
  • Mouth or tongue soreness
  • Depression (2, 3)

Deficiency prevalence increases with age and is primarily due to issues of malabsorption, poor dietary intake, and pernicious anemia.


Malabsorption of B12 is prevalent in people with various gastrointestinal (GI) disorders and GI surgeries.

GI disorders like celiac and inflammatory bowel disease (IBD) reduce the body’s ability to absorb and maintain healthy B12 stores. Additionally, those who undergo GI surgery like removal of intestines and gastric bypass also have difficulty with B12 absorption (4, 5).

Those with atrophic gastritis, a condition depleting stomach acid, reduces B12 absorption. It’s estimated that 10 to 30% of older adults have this condition (6).

Poor Dietary Intake

Vegetarians, particularly those restricting milk and eggs, are at higher risk of B12 deficiency because there are limited plant-based B12-food sources.

In this case, it’s important to incorporate fortified foods or supplements to meet B12 needs. It’s even more vital for pregnant or lactating women who are also vegetarian/vegan to consume enough B12 as infants are at higher risk for B12 deficiency symptoms (7). 

Pernicious Anemia

Pernicious anemia, an autoimmune disease destroying the stomach, reduces the body’s ability to produce intrinsic factor.

Intrinsic factor is a glycoprotein produced in the stomach and required for proper absorption of B12. Intramuscular B12 injections rather than oral B12 helps correct the deficiency. 

Vitamin B12 Testing

Several lab markers assess vitamin B12 status.

Typically, plasma or serum B12 levels are measured, with the ideal range for adults between 170 and 250 pg/mL. Unfortunately, this level doesn’t show B12 levels within the cells and has a low predictive ability (8).

However, homocysteine levels (>13 micromol/L), an amino acid often elevated in relation to inflammation of blood vessels, also helps predict B12 status. Homocysteine is not specific to B12 levels because it may also show folate and vitamin B6 levels. Therefore, this value is used in conjunction with plasma levels to assess B12 status.

Urinary or plasma methylmalonic acid (MMA) (>0.4 micromol/L), a substance produced in the body dependent on B12, is also helpful for detecting early stages of B12 deficiency. However, MMA levels can be elevated in thyroid and kidney conditions which limits the specificity of this test (9, 10).

Lastly, holotranscobalamin (holoTC) (42-157 pmol/L) acutely reflects B12 levels in the body. There is a likelihood of a false positive result if one has kidney issues. This test result should be used in conjunction with serum B12 and MMA and not as a sole measurement (11, 12).

Vitamin B12 Benefits

The body requires adequate B12 levels to prevent a deficiency, however the research on additional benefits of supplemental B12 doesn’t live up to the hype.

While it’s known that B12 along with B6 and folate help metabolize homocysteine levels, it’s not established that B12 supplementation reduces the risk of cardiovascular disease directly (13).

Along those lines, many assume that B12 also supports brain and cognitive function due to its ability to reduce homocysteine levels. However, two Cochrane reviews and a systematic review on this topic didn’t show sufficient evidence to support this claim (14, 15, 16).

Also, many use supplemental B12 to improve energy and physical performance. Once again, the research doesn’t show that surpassing B12 needs provides any additional benefit for these areas either (17).

On the other hand, B12 has been shown to reduce the hepatitis C virus from replicating. When patients with hepatitis C were given standard therapy or standard therapy with 5,000mcg injected B12 every 4 weeks for 48 weeks, those with the additional B12 had a better response to the treatment (18).  

Another proven benefit of B12 is reducing the risk of for acute lymphoblastic leukemia in children when pregnant mothers supplement during the last six months of pregnancy (19).

Foods High in Vitamin B12

Naturally occurring food sources of B12 are animal based like seafood, meat, poultry, eggs and dairy.

There are also fortified foods with B12 including breakfast cereals, nutritional yeast, and infant formulas.

Below is a list B12-containing foods:

FoodMicrograms (mcg)
per serving
Percent DV*
Clams, cooked, 3 ounces84.11,402
Liver, beef, cooked, 3 ounces70.71,178
Breakfast cereals, fortified with 100% of the DV for vitamin B12, 1 serving6.0100
Trout, rainbow, wild, cooked, 3 ounces5.490
Salmon, sockeye, cooked, 3 ounces4.880
Trout, rainbow, farmed, cooked, 3 ounces3.558
Tuna fish, light, canned in water, 3 ounces2.542
Cheeseburger, double patty and bun, 1 sandwich2.135
Haddock, cooked, 3 ounces1.830
Breakfast cereals, fortified with 25% of the DV for vitamin B12, 1 serving1.525
Beef, top sirloin, broiled, 3 ounces1.423
Milk, low-fat, 1 cup1.218
Yogurt, fruit, low-fat, 8 ounces1.118
Cheese, Swiss, 1 ounce0.915
Beef taco, 1 soft taco0.915
Ham, cured, roasted, 3 ounces0.610
Egg, whole, hard boiled, 1 large0.610
Chicken, breast meat, roasted, 3 ounces0.35

Adequate stomach acid and enzymes are required to free up B12 from the proteins it is bound to in food. In cases of compromised stomach functioning, B12-fortified foods and/or B12 supplements allow for better absorption of this nutrient.

Vitamin B12 Supplements

It’s vital to treat a B12 deficiency to avoid permanent nerve damage.

B12 supplements are typically present in the cyanocobalamin form, which must be converted in the body to active-B12, methylcobalamin and 5-deoxyadenosylcobalamin.

To obtain B12 from a supplement, one may explore multivitamin formulations, B-complexes, and taking it as a sole nutrient.

For generally healthy individuals with balanced diets, supplement with B12 alone if needed to correct a deficiency. Potentially supplementing with high levels of unnecessary nutrients can be contraindicated. Also, keep in mind that most foods contain a variety of B-vitamins (i.e. B1, B2, B3, B5, B6 and B7), while B12 can be more limited in the diet. 


Most products provide 500 to 1,000mcg of B12, despite the Recommended Daily Allowance (RDA) being significantly lower than this due to wide variations in absorption rates.

Table 1: Recommended Dietary Allowances (RDAs) for Vitamin B12 [5]
0–6 months*0.4 mcg0.4 mcg  
7–12 months*0.5 mcg0.5 mcg  
1–3 years0.9 mcg0.9 mcg  
4–8 years1.2 mcg1.2 mcg  
9–13 years1.8 mcg1.8 mcg  
14+ years2.4 mcg2.4 mcg2.6 mcg2.8 mcg

* Adequate Intake

Variation in B12 absorption from person to person primarily stems from internal differences, like the amount of intrinsic factor released in the stomach or genetic defects. Even changing the oral supplement to a sublingual tablet or lozenge doesn’t seem to drastically change absorption rates (20, 21).


Intramuscular B12 injections are also used to treat a deficiency. Some don’t prefer this route as it requires a medical professional to administer. However, in cases of severe nutrient malabsorption and pernicious anemia, injections are more efficient at correcting the deficiency.

There are also gel formulations of B12, available as a prescription medication, that is applied to the inside of the nose. While this is an effective method, it hasn’t been carefully studied in clinical trials (22).

High intake of folic acid can mask as B12 deficiency and exacerbate anemia. Limit folic acid intake to 1000 mcg per day from foods and supplements. Additionally, many opt to take supplemental B12 if required to take a folate supplement to avoid this risk altogether (23, 24).

Can Too Much Vitamin B12 Cause Problems?

While high serum B12 levels, also termed hypercobalaminemia (950pg/mL), don’t directly cause side-effects, it can indicate more serious conditions.

Conditions like chronic myelogeneous leukemia, promyelocytic leukemia, polycythemia vera and hypereosinophilic syndrome have all been associated with high B12 levels (25).

Currently there is no established Upper Limit for B12 due to the low potential for toxicity.  


Vitamin B12 is commonly deficient and should be efficiently corrected.

Issues related to malabsorption, poor dietary intake, and pernicious anemia typically cause a B12 deficiency. For those with severe malabsorption due to GI disease or surgery, as well as those with pernicious anemia, it’s ideal to use intramuscular B12-injections. In the case of poor dietary intake, B12 supplements, B12-fortified foods, and natural B12-food sources are all helpful.

While adequate B12 levels are essential for good health, excessive intake is unnecessary and will not provide additional health benefits.

Overall, eating a balanced diet with smart supplementation keeps your B12 levels in check.


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