The Truth About Vitamin B12 Deficiency

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Are vegetarians and vegans really at risk?

Vitamin B₁₂ (cobalamin) is receiving much attention these days. Vitamin B₁₂ is one of the B vitamins implicated in brain and heart health, and it is one of the vitamins most likely to be deficient in the diets of vegetarians and vegans.^[1]

The consequences of vitamin B₁₂ deficiency are profound. During pregnancy, a deficiency of B₁₂ increases the risk of preeclampsia, a serious pregnancy complication characterized by high blood pressure and organ damage.^[2] A prenatal deficiency of B₁₂ and/or folate (vitamin B₉) also increases the infant’s risk of neural tube defects (defects of the brain and spine, such as spina bifida).^[3] In adults, B₁₂ deficiency increases the risk of peripheral neuropathy, depression, osteoporosis, Alzheimer’s disease, heart disease, and stroke.^[4],[5],[6] Sadly, B₁₂ deficiency may even negate the cardiovascular benefits of a vegetarian diet.^[7]

Vitamin B₁₂ is found in significant quantities only in animal foods.

Vitamin B₁₂ is found in significant quantities only in animal foods. It is synthesized by microbes, including the bacteria that live in the rumens (first stomachs) of cows. This explains why B₁₂ is found in significant amounts in meat and dairy products.^[8] Fish acquire vitamin B₁₂ by consuming phytoplankton, which have a symbiotic relationship with bacteria that produce B₁₂. Plants, on the other hand, do not make B₁₂ and do not require it for growth. This simple fact of nature makes B₁₂ a nutrient of concern for vegetarians and especially for vegans, who avoid consuming meat, dairy products, or fish.^[9]

As more people turn to plant-based diets for many reasons, including overall health, nutritionists are raising the alarm about the risks of B₁₂ deficiency.^[10] “Of all the micronutrients, B₁₂ is the one we’re most concerned about,” says Thomas Sanders, professor emeritus of nutrition at King’s College London. “I’m concerned many people think B₁₂ deficiency is a myth.”^[11]

Indeed, some vegan advocates believe that plant foods can provide all the nutrients necessary for optimal health.^[12] We’ve even heard stories like “You can get enough B₁₂ from the soil on your vegetables if you don’t wash them,” and, “You don’t need to supplement with vitamin B₁₂, as you can get enough through the bacteria in your mouth.”

So, what’s the real status of B₁₂ in vegetarians and vegans, and how can you ensure adequate intake of this nutrient if your diet emphasizes plants rather than animal foods?

The vegetarian risk for B₁₂ deficiency

Despite the many benefits of vegetarian and vegan diets, individuals who follow such diets – whether in the UK, US, Europe, India, China, or Australia – tend to suffer from insufficient dietary B₁₂ intakes.^{[1],[13],[14],[15],[16],[17]}

Without adequate dietary or supplemental B₁₂, signs of deficiency gradually appear. These may include fatigue, weakness, constipation, problems with balance, mental fogginess, tingling and numbness in the hands and feet, depression, and megaloblastic anemia (the formation of large and structurally abnormal red blood cells).^[18]

A functional B₁₂ deficiency can occur in the presence of normal serum levels.

Since the neurological symptoms of deficiency are fairly nonspecific, vitamin B₁₂ deficiency is often overlooked in clinical practice.^[19] Many physicians do not think of testing for nutrient deficiencies, or they may think that the serum vitamin B₁₂ level is a good marker of B₁₂ status. However, studies have shown that a functional B₁₂ deficiency can occur in the presence of normal serum levels.^{[1],[7],[18],[20]}

The most accurate markers of B₁₂ status are holotranscobalamin (the biologically active form of vitamin B₁₂ in the blood) and/or methylmalonic acid (MMA), a substance produced in very small amounts during cellular metabolism.^[7] Vitamin B₁₂ is needed for the metabolism of MMA, so a buildup of MMA is a sign that cellular B₁₂ supplies are too low.^[18],[20]

In 2017, researchers evaluated vitamin B₁₂ status (MMA levels) in young adults who were either omnivores, who ate all types of food, or were vegetarians.^[21] Except for the small consumption of dairy products, the vegetarians ate no animal-sourced foods such as meat, poultry, fish, or eggs. While all the omnivores had normal MMA levels, 44% of the vegetarians had elevated levels, indicating the presence of B₁₂ deficiency.

Vegetarians are more prone to developing neuropsychiatric and neurological problems than omnivores, a consequence of inadequate B₁₂ intake.

These participants were also evaluated by a neurologist, psychiatrist, and general physician. They found that the incidence of peripheral neuropathy, depression, and psychosis was three- to fourfold higher in the vegetarians than in the omnivores.^[21] Clinical depression was observed in 31% of vegetarians, compared with only 12% of omnivores. The authors concluded that vegetarians are more prone to developing neuropsychiatric and neurological problems than omnivores, a consequence of inadequate B₁₂ intake.

The good news is that early correction of B₁₂ deficiency through supplementation with vitamin B₁₂ (and other B vitamins, if they are deficient as well), can prevent the neurological problems associated with B₁₂ deficiency.^{[22],[23],[24]}

Malabsorption, age, and medications associated with B₁₂ deficiency

Lower vitamin B₁₂ intakes are associated with a greater risk of dementia and Alzheimer’s disease.

Problems with B₁₂ absorption can also cause a deficiency of the vitamin. This is quite common in older individuals, because the stomach loses its capacity to extract B₁₂ from food as we age.^[25] Lower vitamin B₁₂ intakes are associated with a greater risk of dementia and Alzheimer’s disease.^{[24],[26],[27]}

People with celiac disease, pancreatic insufficiency, or weight loss surgery may also have trouble absorbing vitamin B₁₂.^{[28],[29],[30]} Inadequate dietary intake and poor absorption contribute to deficiencies in celiac disease.^[31] Studies suggest that more than 40% of newly-diagnosed celiac disease patients may be deficient in B₁₂, making supplementation a good idea for this group.^[32]

The absorption of vitamin B₁₂ depends on the presence of a protein produced in the stomach known as intrinsic factor. In a rare but serious autoimmune condition known as pernicious anemia, the body produces antibodies to intrinsic factor, resulting in B₁₂ deficiency.^[33]

Vitamin B₁₂ absorption is also impaired by medications such as antacids, proton pump inhibitors, and the diabetes drug metformin.^{[34],[35],[36]} One study found that 22% of diabetic patients had B₁₂ deficiency, based on MMA and homocysteine levels (homocysteine is discussed later in this article).^[37]

An unfortunate contributor to B₁₂ deficiency is the use of nitrous oxide (N₂O) as a party drug. Used by hundreds of thousands of adolescents and young adults, N₂O is an anesthetic gas that inactivates vitamin B₁₂ by oxidizing the cobalt atom at the core of the B₁₂ molecule.^{[38],[39],[40]} The symptoms of overuse include tingling and numbness in the hands and feet, which may progress to spinal cord degeneration.^[41] Lasting damage can be prevented by B₁₂ supplementation if it is begun early enough.^[42]

Are vegan sources of B₁₂ reliable?

Vitamin B₁₂ intake in vegans is only 10% to 20% of the RDA.

Nutritional analyses confirm that vegan meal plans do not meet the Recommended Daily Allowance (RDA) for vitamin B₁₂ without supplementation.^[43] As a result, vitamin B₁₂ intake in vegans is only 10% to 20% of the RDA, as shown in a systematic review of 48 published studies.^[44]

Some plant milks, tofu, and other prepared vegetarian foods are fortified with vitamin B₁₂. However, it would be necessary to consume large amounts of these products to reach the desired levels.^[45]

Vegan proponents often claim that spirulina, chlorella, certain mushrooms, seaweed, and/or fermented foods can be used to meet the B₁₂ needs of vegans. However, the B₁₂ content of such foods may vary by 100-fold, making them unreliable sources of this vitamin.^{[25],[46],[47]} Additionally, spirulina and some algae contain inactive forms of B₁₂ that can attach to B₁₂ receptors, preventing absorption of the nutrient and promoting deficiency.^[45]

Chlorella (green algae) has been touted as solving the “B₁₂ problem” for vegans.  To support this claim, a clinical study examined the effects of Chlorella pyrenoidosa supplementation in 17 vegans who had elevated MMA levels.^[48] The ingestion of chlorella (9 grams/day) helped reduce average MMA levels after one to two months. However, functional B₁₂ deficiencies (elevated MMA levels) persisted in 41% of the subjects after 60 days. Moreover, the protocol required that participants consume 45 tablets of Chlorella every day.  Needless to say, swallowing that many tablets on a daily basis would be challenging over the long term.

Studies of thousands of vegetarians and vegans have shown that they are susceptible to B₁₂ deficiency unless they take supplements containing the vitamin.

The myths about vitamin B₁₂ – that you can get enough B₁₂ from the soil on your vegetables if you don’t wash them, or that you don’t need to supplement with vitamin B₁₂ as you can get enough through the bacteria in your mouth – have been debunked.^[49] Studies of thousands of vegetarians and vegans have shown that they are susceptible to B₁₂ deficiency unless they take supplements containing the vitamin.^{[25],[45],[50],[51],[52]}

In addition to providing adequate B₁₂ for neurological function, supplemental vitamin B₁₂ helps maintain normal levels of homocysteine, a byproduct of amino acid metabolism within the body. Elevated homocysteine levels increase the risk of blood clotting, heart disease, and stroke, and B vitamin supplementation has been suggested to reduce these risks.^{[6],[53],[54]}

How much vitamin B₁₂ should we consume?

The Academy of Nutrition and Dietetics, which represents over 100,000 credentialed practitioners, has issued the following recommendations for vegetarians and vegans:^[55]

• Vegetarians and vegans should be screened periodically for B₁₂ deficiency.
• Vegans should take 250 mcg per day of a vitamin B₁₂ supplement. (This amount is about 100 times higher than the RDA, due to the fact that only about 1% of ingested B₁₂ from supplements is absorbed.)
• Lacto-ovo vegetarians (those who consume milk and eggs, but not meat) should consider taking 250 mcg of a B₁₂ supplement a few times per week.

Due to problems with B₁₂ absorption with age, many nutritionists also recommend that older adults supplement with B₁₂ to avoid deficiency.^[56],[57] The preferred form of vitamin B₁₂ for supplementation is methylcobalamin, a biologically active form, as compared to cyanocobalamin, which is not found in nature and must be metabolized.^[6]

If you are diagnosed with B₁₂ deficiency, your doctor may recommend higher supplemental doses of up to 1,000 mcg/day to correct MMA levels.^{[7],[58],[59],[60]} Fortunately, oral vitamin B₁₂ doses have been shown to be safe and effective, and injections are generally not required.^[59],[61]

In conclusion, it’s worth paying attention to your B₁₂ intake, regardless of the type of diet you typically consume. Vegetarians and vegans, older adults, individuals with celiac disease, and many other groups are at risk for B₁₂ deficiency, and the consequences of inadequate intakes can be profound. Regular supplementation with B₁₂ and other essential micronutrients helps ensure adequacy and promote overall health throughout life.

If you enjoyed this article, you may also be interested in the following posts:

• Is a Vegan Diet Healthy? The pros and cons of going vegan.
• Breaking Bad: Homocysteine and Aging: The role of B vitamins in cardiovascular and neurological health.
• B Vitamins for Brain Health: Simple-yet-powerful nutrients to fight depression, dementia, and more.

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