How Much B12 Do I Need To Lose Weight

These are just three of the common myths floating around the plant-based community surrounding vitamin B12 intake and vegan diets. In fact, some popular vegan websites and publications hold the philosophy that vegans can meet all of their essential nutrient needs without the use of any supplements.

To be sure, this viewpoint isn't prevalent among all plant-based experts and websites. Most respected sources place great emphasis on supplementing the vegan diet with adequate B12 sources. The Vegetarian Resource Group suggests that vegans need to have reliable sources of vitamin B12 in their diets.1 The Vegetarian Nutrition Dietetic Practice Group (VNDPG) of the Academy of Nutrition and Dietetics (the Academy) says that all vegetarians (including vegans) should include a reliable B12 source in their diets, such as fortified foods or supplements.2 And The Vegan Society goes so far as to state, What every vegan should know about B12: the only reliable sources of B12 are foods fortified with B12 and supplements.3

It's extremely important for health care professionals—as well as clients—to understand the significance and intricacies of sufficient vitamin B12 intake for vegan diets, because deficiency of this essential micronutrient is serious business.

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Vitamin B12 is a water-soluble vitamin that contains the mineral cobalt and exists in several forms. Compounds with vitamin B12 activity are called cobalamins. Methylcobalamin and adenosylcobalamin are two forms that are active in human metabolism. The other forms are hydroxocobalamin and cyanocobalamin that must be metabolized into the two active forms to be used in human cells. B12 analogues—inactive forms—may be found in algae and some plant foods.2, 4, 5

Vitamin B12 is needed for proper red blood cell formation, neurological function, and DNA synthesis. The vitamin is a cofactor for methionine synthase, which catalyzes the conversion of homocysteine to methionine—required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 substrates, including DNA, RNA, hormones, proteins, and lipids. Methionine also is needed for the synthesis of myelin, a coating of the nerve pathways. Vitamin B12 is a cofactor for L-methylmalonyl-CoA mutase, which converts L-methylmalonyl-CoA to succinyl-CoA in the degradation of propionate, an essential biochemical reaction in fat and protein metabolism. Succinyl-CoA also is required for hemoglobin synthesis.2, 4

B12 digestion and absorption requires the adequate synthesis of hydrochloric acid, proteases (enzymes that break down proteins and peptides), and intrinsic factor (a glycoprotein secreted in the stomach). The vitamin is released from dietary proteins by pepsin (an enzyme secreted in the stomach) and activated by hydrochloric acid. B12 binds with proteins secreted in the saliva, and in the small intestine pancreatic proteases digest the proteins, liberating the B12 to form a complex with intrinsic factor. Vitamin B12 can then be absorbed into the bloodstream via endocytosis in the distal ileum, or by passive diffusion in the absence of intrinsic factor.2

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Pernicious anemia (an autoimmune disease) affects the gastric mucosa, leading to destruction of parietal cells and failure to produce intrinsic factor, resulting in vitamin B12 malabsorption and eventually deficiency. Older adults, who often suffer from decreased hydrochloric acid in the stomach, and individuals with gastrointestinal (GI) disorders may have lower absorption of B12.2, 4

Vitamin B12 deficiency may be characterized by megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, soreness of the mouth or tongue, and weight loss; and neurological conditions, such as numbness and tingling of the hands and feet, difficulty with balance, depression, confusion, dementia, and poor memory. The neurological symptoms can occur without the presence of anemia, thus early detection is important to avoid irreversible damage. Deficiency is also commonly misdiagnosed, because symptoms can mimic other conditions.2, 4

Large intake of folic acid—common in vegan diets—can mask the damaging effects of B12 deficiency by correcting anemia without addressing the neurological damage that occurs. High folic acid may even exacerbate anemia and cognitive symptoms. It isn't recommended to exceed 1, 000 mcg/day of folic acid in healthy adults.4

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Vitamin B12 is only synthesized by microorganisms. Thus, it isn't found in foods of plant origin. Natural animal food sources of vitamin B12 (which come from the animal's intestines or from their diet) include fish, meat, poultry, eggs, milk, and milk products. Though some bacteria in the small intestines produce B12, it isn't enough to maintain adequate status in humans.2, 4

According to Jack Norris, RD, a vegan expert and coauthor of Vegan for Life: Everything You Need to Know to Be Healthy and Fit on a Plant-Based Diet, there are no reliable sources of B12 in plants, contrary to many rumors about sources such as tempeh, seaweeds, and organic produce. Plants have no B12 requirement; therefore, they don't have any active mechanisms to make or store it. When you find B12 in plants, it's due to contamination and thus isn't a reliable source. Many seaweeds have B12 analogues through their symbiotic relationship with cobalamin-producing bacteria; however, the evidence isn't clear that this form is active B12 in humans. And fermented foods, such as tempeh, aren't fermented through B12-producing bacteria, thus they aren't a source of B12. Rumors about bacteria on the surface of organic produce producing B12 haven't been verified. Chlorella may improve B12 status, but it's by such a small amount that I wouldn't rely on chlorella for B12, Norris adds. He stresses that unless a food obtained from multiple regions consistently improves B12 status, it shouldn't be relied upon as a source of B12.5

Naturally, vegetarians—especially vegans—are at risk of vitamin B12 deficiency. In fact, there's a high prevalence of low serum vitamin B12 among vegetarians, in particular vegans, where prevalence ranges at levels between 43% and 88%.6 Going back as far as 1955, studies have shown that vegans have experienced vitamin B12 deficiency.7 In addition, B12 crosses the placenta during pregnancy and is present in breast milk—thus, if the mother doesn't receive adequate B12 intake, infants may suffer from B12 deficiency, which can lead to severe, permanent neurological damage.4

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Norris says the story doesn't end there. He reports that most vegans show adequate B12 levels to make clinical deficiency unlikely, but they may show restricted activity of B12-related enzymes, leading to elevated homocysteine levels, which has been linked to increased risk of heart disease and stroke. Thus, he warns that repeated observations of elevated homocysteine levels in vegans show that B12 intake must be addressed.

The RDA for B12 in adults is 2.4 mcg per day (see Table 1), which assumes a 50% absorption rate from the amount ingested in foods. However, higher levels may be recommended to prevent potential deficiency symptoms in vegans. Intake of higher doses doesn't appear to be associated with detrimental health problems.2

Norris recommends vegan adults 18 to 65 years old should take one of the following regimens: two doses per day of 2 to 3.5 mcg per serving, one dose per day of 25 to 100 mcg per serving, or two doses per week of 1, 000 mcg per serving. To read his full recommendations, visit http://veganhealth.org/b12/rec.8

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In supplements, B12 is usually present as cyanocobalamin—a form the body readily converts into the active forms methylcobalamin and adenosylcobalamin. Other forms may be present in supplements, such as methylcobalamin and hydroxocobalamin. The vitamin B12 forms cyanocobalamin and occasionally hydroxocobalamin can be administered by intramuscular injection to treat deficiency or cases of malabsorption. While absorption may not differ among forms of B12, the body's ability to absorb the vitamin is largely limited by the capacity of intrinsic factor.2, 4

Many foods are fortified with B12, including breakfast cereals, meat analogues, soymilk, and nutritional yeast (see Table 2). They may be fortified from small amounts to more than 200% of the RDA. It's important to read labels, as not all of these products are fortified, and fortification can change in products over time.2 Norris reports that amounts listed on a nutrition label are based on 6 mcg per day. For example, a food that provides 25% DV for B12 would provide 1.5 mcg.8

The status of B12 typically is assessed through serum or plasma B12 levels. Values below 170 to 250 pg/mL for adults indicate a deficiency. However, this indicator may be influenced by other factors, such as low vitamin B6 or folate levels. Elevated MMA levels (greater or equal to 0.4 mcmol/L) may be a more reliable indicator of B12 status, because it indicates metabolic changes more specific to B12 deficiency.4

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Norris recommends MMA and serum vitamin B12 tests for vegans, adding, You don't need to get tested just because you're vegan; rather, you should make sure you follow the recommendations for intake.

Reed Mangels, PhD, RD, LDN, a vegan nutrition expert and associate professor of nutrition at the University of Massachusetts Amherst, also looks at MMA, as well as homocysteine levels, to see if B12 status is adequate. B12 works with other B vitamins in many biochemical cycles, so it's important to understand the whole picture and look at a variety of nutrients, she says.

So, what can dietitians do to clear up confusions on B12? The first step may be identifying some of the common myths. Norris says, There's less confusion than during the 1990s and early 2000s, but there's still a lot. Many

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