This article will summarize all of the must-know information about vitamin b12 nutrition for registered dietitians.
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Written by Miranda Galati, RD
Medically reviewed by Olivia Farrow, RD, MHSc
Vitamin B12 Nutrition
Vitamin B12, or ‘cobalamin’, is a water-soluble nutrient that is important for red blood cell formation and neurological function (1, 2). B12 is found in animal foods such as meat and dairy, fortified breakfast cereals, and supplements (1, 3).
Vitamin B12 is one of eight B vitamins, which are collectively important for energy metabolism and cell function (1, 4, 5, 6, 7, 8, 9, 10).
B12 Role in the Body
B12 plays many important roles in metabolism, cell formation and neurological function (2). More specifically, B12 is involved in:
- The development, myelination and function of the nervous system (1, 13, 14)
- Red blood cell formation (1)
- DNA synthesis (1)
- Different enzyme reactions as a cofactor (1, 15)
B12 Health Benefits
There is mixed evidence about whether B12 status in the body directly impacts:
- Cancer risk and prevention (1, 16, 17)
- Cardiovascular disease risk (1, 18, 19)
- Dementia and Alzhiemer’s disease risk (1, 20, 21)
More evidence is needed to determine whether B12 is relevant to the development and/or progression of these ailments (1).
There are also claims that B12 supplementation can boost energy or improve cognitive function. While B12 deficiency can certainly impact energy and cognition, supplementation is only found to improve these markers for people with suboptimal levels (1).
Learning how B12 is absorbed and utilized in the body helps to understand the cause and treatment of deficiency and choosing between the different types of b12 supplements. Here are some key points to be aware of:
- B12 is bound to proteins in food and must be released to be absorbed (1).
- The process of B12 detaching from protein mostly occurs in the stomach with the help of proteases and hydrochloric acid (HCl) (1).
- B12 must bind with intrinsic factor in the duodenum to be absorbed in the ileum (1).
B12 deficiency may have a variety of causes including:
- Diet lacking in animal products
- Abnormalities with HCl or proteases in the stomach
- Low production of intrinsic factor (pernicious anemia)
- Injuries or inflammation in the small intestine (inflammatory bowel disease, gastrointestinal surgery).
Vitamin B12 Nutrition: Food Sources
B12 is found in food sources such as fish, meat, poultry, eggs and dairy products (1). It is also found in fortified breakfast cereals and fortified nutritional yeast (1). Refer to the table below for a more complete list of food sources and their B12 content (1).
Food Sources of Vitamin B12
|Food||Serving||B12 per serving (mcg)|
|Beef liver, cooked||3 ounces or a palm-sized portion||70.6|
|Clams, cooked||3 ounces or a palm-sized portion||17|
|Tuna, bluefin, cooked||3 ounces or a palm-sized portion||9.3|
|Nutritional yeast, fortified (check label)||¼ cup||8.3-24|
|Salmon, atlantic, cooked||3 ounces or a palm-sized portion||2.6|
|Ground beef 85% lean, cooked||3 ounces or a palm-sized portion||2.4|
|Milk, 2%||1 cup||1.3|
|Yogurt, plain, fat-free||6-ounce container or ¾ cup||1.0|
|Breakfast cereals, fortified with 25% DV||1 serving||0.6|
|Cheese, cheddar||1.5 ounces or a thumb-sized portion||0.5|
|Egg, whole, cooked||1 large||0.5|
|Turkey breast, meat, roasted||3 ounces or a palm-sized portion||0.3|
*Values are approximate and may vary by database and/or brand. (1, 24)
B12 bioavailability varies, for example:
- B12 in dairy products is three times more bioavailable than B12 in meat, fish and poultry (1) However, the quantity of B12 is still lower in dairy than in most meats and fish (see table above).
- B12 from fortified foods has high bioavailability because it is in its free form and does not require separation from protein (1).
- B12 from supplements has 50% higher bioavailability than B12 from food sources for the same reason (1).
Vitamin B12 Nutrition Through Diet
Most people can obtain adequate B12 through the diet by eating a variety of animal products such as meat, fish, poultry, eggs and dairy (1). People who have limited or no intake of animal products should consider supplementation (1).
Causes of B12 Deficiency
There are many factors that may contribute to B12 deficiency or low B12 levels, including:
- Low B12 intake due to vegetarian diet, vegan diet, chronic alcoholism or old age (22)
- Autoimmune conditions such as pernicious anemia and Sjorgren’s syndrome
- Malabsorption due to gastritis, small intestinal bacterial overgrowth (SIBO), chronic pancreatic insufficiency, Crohn’s disease and celiac disease (22)
- Surgery such as post-gastrectomy or ileal resection (22)
- Obstetric or gynecological factors such as oral contraceptives, hormone replacement therapy and pregnancy (22)
- Genetic factors such as a transcobalamin II deficiency (22)
- Use of certain drugs such as metformin, proton pump inhibitors, and histamine H2 receptor antagonists (22)
B12 deficiency may be characterized by:
- Glossitis of the tongue (1)
- Fatigue or pale skin (1)
- Heart palpitations (1)
- Weight loss (1)
- Mouth ulcers (28)
- Dementia or depression (1, 22)
- Neurological changes such as tingling of the hands and feet (1)
Symptoms of B12 deficiency can take years to appear. This is because the body stores 1-5 mg of B12, which is 400-2000 times the RDA(1). For this reason, providers should be proactive in looking for signs and risk factors of suboptimal intake or blood levels (1).
Impacts of B12 Deficiency
Long-term B12 deficiency may lead to megaloblastic anemia, which is characterized by unusually large red blood cells (1, 29). With or without the development of megaloblastic anemia, B12 deficiency may lead to serious and sometimes irreversible health complications, including:
- Neurological problems such as poor memory, paresthesias, vision loss, ataxia, and peripheral neuropathy (29)
- Infertility (29)
- Gastric cancer (29)
- Neural tube defects in fetuses that may lead to spina bifida or anencephaly (29).
Supplementation is important at the first signs of deficiency to minimize any long-term impacts (1).
Indications for B12 Supplementation
Individuals with diagnosed B12 deficiency or those at risk for deficiency may consider supplementation. This includes:
- Older adults due to low intake or malabsorption (22).
- Individuals with pernicious anemia due to low production of intrinsic factor and malabsorption (22).
- Individuals with gastrointestinal disorders due to malabsorption (22).
- Individuals who have had gastrointestinal surgery due to malabsorption (22).
- Exclusively breast-fed infants of vegan mothers if the mother has low B12 reserves (22).
- Women who are pregnant or breastfeeding due to increased needs (1).
- Individuals following a vegan or vegetarian diet due to low intake (22).
B12 Supplementation Instructions and Dosages
Individuals with diagnosed B12 deficiency are often treated with prescription intramuscular B12 injections (1). This is done to bypass any potential issues with absorption that may be contributing to ongoing deficiency (1). Some evidence suggests that very high doses (1000-2000 mcg) through oral supplementation may adequately treat deficiency (1, 30). The best treatment method for vitamin B12 deficiency is at the discretion of the physician (1).
Individuals at risk for deficiency may consider oral supplementation (1), with the following guidelines in mind:
- Choose a B12 supplement and not a B vitamin complex unless a physician has indicated the need for additional B vitamin supplementation (1).
- Dosages of 500-1000 mcg should be sufficient unless an individual is facing severe malabsorption concerns (1).
- The most common form of B12 in supplements is cyanocobalamin, this and the other types of b12 supplements (adenosylcobalamin, methylcobalamin, and hydroxycobalamin) are reviewed thoroughly in DSC’s B12 summary guide for dietitians.
- Only 50% or less of B12 from oral supplements may be absorbed, despite having higher bioavailability than B12 from food (1).
B12 Supplementation Contraindications and Risks
The risks of oral B12 supplementation are limited. B12 has low potential for toxicity because the body does not store excess amounts, so the concern for high intake is minimal (1).
Concern for medication interactions are mainly because certain drugs can inhibit B12 absorption and increase the risk of deficiency. These medications include:
- Oral contraceptives (22)
- Metformin used for prediabetes and diabetes (1)
- Proton pump inhibitors used for reflux or peptic ulcer disease (1, 22)
- Histamine H2 receptor antagonists used for ulcers (22)
Encourage your clients to consult their healthcare provider, pharmacist and/or dietitian before beginning a new supplement.
Vitamin B12 Nutrition: Take-Home Messages for Dietitians:
- Vitamin B12 is a water-soluble nutrient involved in energy metabolism, cell function and neurological activity.
- B12 from food must be separated from protein, combined with intrinsic factor, and absorbed in the small intestine to be used in the body. Health conditions that impact one of these processes can lead to deficiency.
- Vitamin B12 is found in animal-based foods such as fish, poultry, meat, eggs and dairy products. It is also found in fortified foods, supplements, and prescription medication delivered intravenously.
- B12 deficiency may be caused by low intake, medication interactions or malabsorption. People at highest risk of deficiency include individuals with pernicious anemia, individuals with gastrointestinal disorders or surgery, breast-fed infants of vegan mothers, individuals following a vegan or vegetarian diet, and the elderly.
- Oral supplementation of vitamin B12 in dosages of 500-1000 mcg per day is generally regarded as safe.
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