Vitamin B12 and Vegetarian Diets

Vitamin B12 (B12) is essential in the synthesis of all new cells and maintenance of myelin, a coating of the nerve pathways. B12 deficiency is a worldwide problem. A deficiency may result from inadequate intake, malabsorption or a genetic mutation. Depending on the study, 11 to 94% of vegetarians were reported as having a deficiency. Deficiency rates often exceed 50%. Two studies assessed B12 status among members of the Seventh-day Adventist Church. There was a 40% deficiency prevalence among the 25 vegans included in the first study. Similarly, close to 50% of vegans and close to one third of lacto-ovo-vegetarians, participants of the Adventist Health Study II, were reported as having a deficiency. About one-third of non-vegetarian Adventists also had B12 deficiency. Although a higher deficiency prevalence is usually reported among vegans, compared to other vegetarians, most studies found high deficiency prevalence in all vegetarians, regardless of other factors, such as demographic characteristics, place of residency, or age.

Especially worrisome should be a high number of published case studies with B12 deficiency among infants and children born to vegan women. Long-term complications, related especially to neurological manifestations, that often include severe developmental delays, are not uncommon. Case reports among vegetarian, especially vegan, adults are also common.

Deficiency symptoms include manifestations in blood cells, skin, gastrointestinal tract, neurological and psychiatric. B12 deficiency is associated with high serum homocysteine concentration, a substance that has been associated with increased risk of cardiovascular disease, bone fractures, dementia, diabetes complications (e.g. abnormal eye, kidney and nerve function), and some forms of birth defects, such as spina bifida. B12 deficiency leads to infertility and/or spontaneous abortion. B12 deficiency in infants and children leads to severe, long-term neurological complications and developmental delays. Other B12 deficiency symptoms include lack of energy, weakness, fatigue, forgetfulness, lightheadedness, tingling and burning sensation, numbness, muscle imbalance, tremors, changes in skin color, synthesis of large and immature red blood cells, glossy and “beefy” color of the tongue, and myelin deterioration. If untreated, even more severe complications, such as paralysis, paranoia, hallucinations, stroke and dementia may occur.

B12 is not found in foods of plant origin. Very small amounts of B12 may be found in some plant foods due to contamination during processing, the addition of small amounts of animal-derived ingredients or fortification. However, the amount of B12 found in these foods, except for foods that have been fortified, is negligible. Milk, dairy products and eggs contain small amounts of B12. However, B12 intake from these products is likely inadequate to maintain sufficient serum B12 concentration. Fermented soy products, such as tempeh and other plant foods, do not contain biologically active forms of B12. B12 synthesis by bacteria in the small intestine is negligible. Similarly, the use of probiotics does not improve vitamin B12 status. Research findings regarding algae, such as spirulina, nori, kombu and Chlorella showed that they are not reliable in improving B12 status. Furthermore, some of these products contain large amounts of pseudo vitamin B12 which may interfere with true B12 metabolism.

Vegetarians need to ensure they ingest a reliable B12 source. Relying on ingesting eggs, milk and dairy products does not ensure adequate B12 status. Although fortified foods may help to delay the onset of deficiency, deficiencies have been reported among vegetarians who used fortified foods and even among those who used supplements (perhaps indicating inadequate dose of a supplement). Because food fortification practices change and B12 content of eggs and dairy products is variable and subjected to food preparation (e.g. cooking destroys B12), the most reliable way for vegetarians to ensure adequate B12 status is to use adequate dose of vitamin B12 via supplements. The dose of a supplement depends on age and lifecycle. Higher doses (e.g. 500 μg/day) should be used by pregnant women and elderly individuals. Lower doses (e.g. 25 to 250 μg/day) should be adequate for most adults. Doses between 5 to 25 μg/day will likely be sufficient for most children and teens.

Vegetarians should periodically (e.g. every 6 to 12 months) check their B12 status. B12 status can be determined using several techniques, including serum or plasma B12, holotranscobalamin II (holoTCII), serum or urinary methylmalonic acid (MMA), serum homocysteine (tHcy), and mean corpuscular volume (MCV). HoloTCII and MMA are the most accurate, whereas serum or plasma B12 and, especially MCV, are less reliable. Reference values for these biomarkers are given in the table below.

b12 assessment table

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