Vitamin B12 is necessary for a laundry list of crucial functions, including DNA synthesis, red blood cell production, and the development and maintenance of the nervous system. It is also a vitamin that many of us do not have sufficient levels of. Because of the variability and general nature of deficiency symptoms, and current testing standards that are set so low, a diagnosis is often missed, leading to increased neurological deterioration and possibly irreversible neurological damage.

B12 is often thought of as an energy booster, and while it is necessary to make energy, we are doing ourselves a huge disservice by stopping the conversation there. Did you know that the normal structure and function of the entire nervous system (including the brain) depends on sufficient levels of the vitamin—from the time we are conceived to old age? It is required for neurotransmitter production and the synthesis and maintenance of the myelin sheath, the protective covering that surrounds nerves and facilitates communication between neurons. It should come as no surprise then, that many of the symptoms of a B12 deficiency are neurological in nature.^{1 2 3} The vitamin is so important to health that severe deficiencies can lead to birth defects in infants and resemble Alzheimer’s disease in adults.⁴

Signs of a B12 deficiency can be easily overlooked, as they can be general, slow to develop, and may be confused with other health conditions (especially if blood levels fall in the normal or low-normal range). Symptoms can include deep fatigue, numbness and tingling in the hands and feet, difficulty walking, dizziness, irritability, depression, and poor memory or memory loss. Extreme deficiency can lead to dementia and may resemble Alzheimer’s disease. Deficiency in infants may manifest as failure to thrive, developmental delays, and megaloblastic anemia, while children with deficient levels may experience social and cognitive delays and stunted growth.^{5 6 7 8}

How common are deficiencies? Because current U.S. testing levels are set so low (<200 pg/mL), many experts believe that the true number of deficiencies is underestimated. If the Framingham Offspring Study—a large population study including 2,999 subjects between the ages of 26 and 83—is any indication, then nearly 40 percent of us have marginal levels—levels at which many people begin to experience neurological symptoms. The study also found that 17 percent were near deficient, and nine percent had an outright deficiency. A surprising find was that younger people were just as likely to have low levels as the elderly, refuting the notion that only older adults are at risk for a B12 deficiency. It is notable that those who took B12 supplements were significantly less likely to be deficient compared to those who did not supplement.¹⁰

Possibly even more worrisome than an outright deficiency—which is easier to diagnose and correct by current testing standards—is a “functional” B12 deficiency. In a functional deficiency, blood levels look normal but patients still exhibit deficiency symptoms; however, because their B12 levels fall in the normal range, they are not treated as if they have a true deficiency, leaving the door open for neurological deterioration if B12 levels are not restored. According to the CDC, these functional deficiencies are far more common than outright deficiencies, and could play a role in the early stages of the development of a number of neurological conditions. Studies have suggested that a daily dose of 500-1,000 mcg can correct a functional deficiency, though some people may need more.^{11 12 13 14}

It is interesting to note that in Japan, where the lower limit for a B12 deficiency is set much higher than the United States (between 500-550 pg/mL vs. <200 pg/mL), the rates of Alzheimer’s and dementia are very low. Some experts speculate that these low rates are due in part to Japan’s proactive policy of recognizing and treating B12 deficiencies.¹⁵

The list of those at risk for a deficiency or functional deficiency is long and varied and includes: vegetarians and vegans; carriers of certain genetic mutations such as the MTHFR variation; those with pernicious anemia (an autoimmune disorder in which the body cannot absorb vitamin B12); anyone with an unhealthy gut (e.g. celiac, Crohn’s, bacterial overgrowth); older adults; heavy drinkers; frequent users of common medications such as antacids, acid blockers, aspirin, and the diabetic drug metformin; and anyone who has had stomach stapling surgery for weight loss.^{16 17 18}

Furthermore, B12 requirements increase for pregnant and lactating women—low or marginal vitamin B12 levels during pregnancy significantly increase the risk for neural tube birth defects, birth defects that occur during the development of the brain and spinal cord.²⁰ Low levels in mothers can also lead to deficiencies or insufficient levels in their infants, which can negatively affect growth and cognitive development, even years down the road.²¹

An especially striking find from the Framingham Offspring Study was that those who consumed the most meat, the main food source of B12, did not have higher blood levels of the vitamin, leading the researchers to conclude that the B12 is simply not being absorbed.²² The way that our bodies absorb B12 from food is a complex process, one that requires sufficient hydrochloric acid and intrinsic factor protein in the stomach—in other words, it a process that requires a healthy gut. So the problem is not a lack of the vitamin in our diets (unless you are vegan) but rather, a modern lifestyle that has created a lot of unhealthy guts, which prevent the vitamin from being absorbed. The bottom line is this: If you regularly take aspirin, antacids, proton-pump inhibitors such as Prilosec, or the diabetic drug metformin, you aren’t absorbing enough vitamin B12, even if you eat a lot of animal products. Further, if you have gastrointestinal issues such as Crohn’s disease, celiac, gastritis, H. pylori infection, or bacterial overgrowth, you are not absorbing B12. If you have low stomach acid (extremely common in older adults), you are not properly absorbing B12. Or if you are a heavy drinker, you are not absorbing enough B12. Many people simply can’t absorb enough B12 from food, no matter how much B12-containing food they eat.

The National Institutes of Health considers someone to be vitamin B12 deficient when their blood serum levels fall below 200 pg/mL (too low, according to many experts), but notes that deficiency symptoms may appear at serum levels between 200-500 pg/mL, which is within the “normal” range.²³ While blood tests are used to confirm an obvious deficiency, they miss functional deficiencies. Malabsorption issues especially can result in body tissues not receiving enough B12 even when serum levels appear normal. Much more accurate test for homocysteine and methylmalonic acid (MMA), which will confirm tissue B12 deficiencies when blood serum levels are in the normal range.^{24 25} A number of studies have shown that patients in the low-normal range who exhibit neurological symptoms show significant improvement with vitamin B12 supplementation.^{26 27}

There are several forms of B12 supplements available, including cyanocobalamin, hydroxocobalamin, and methylcobalamin. The latter is the biologically active form and is the better choice for those with genetic mutations such as MTHFR variation and other absorption issues. Vitamin B12 is considered safe, and has not been shown to be toxic, even at levels much higher than the recommended dose. ^{28 29}

If you suspect that you have low levels of B12, be proactive. Get tested, know what your levels are, and work with your healthcare practitioner to figure out what may be causing it. Once you have this bit of information, it is easy to work toward restoring your B12 levels, while potentially halting bigger problems that could manifest down the road if you don’t.

Are you vegan? Are you supplementing with vitamin B12? If not, you are jeopardizing your health. The only foods that naturally contain vitamin B12 are meat, eggs, dairy, and other animal products—plants do not contain B12. According to The Vegan Society, an organization whose mission is to promote the vegan diet, “B12 is the only vitamin that is not recognized as being reliably supplied from a varied wholefood, plant-based diet…”³⁰ This puts vegans (and some strict vegetarians) at a high risk for developing a B12 deficiency. In fact, studies consistently show that vegans have high rates of B12 deficiencies.^{31 32 33 34 35} Especially worrisome is the effect that a B12 deficiency has on children. One study found that 65 percent of adolescents who ate a vegan diet until the age of six still had a B12 deficiency many years later, even after they began eating meat products. Other research found that older children (10-18 years old) who ate a vegan diet until the age of six scored significantly lower on cognitive tests compared to omnivorous controls, specifically in areas involving reasoning, problem-solving, and the ability to learn.^{36 37}

Some argue that algae, spirulina, brewer’s yeast, and other plant foods supply B12, but they contain B12 analogs that can block the uptake and metabolism of true B12, further reducing B12 status. It is crucially important for vegans of all ages to supplement with B12 to avoid a dangerous deficiency. If you are vegan you should have your B12 levels tested annually; opt for a homocysteine or methylmalonic acid (MMA) test, as a blood serum test can mistake B12 analogs for true B12, providing unreliable results.

The United States is experiencing a mental health crisis—diagnoses of depression, anxiety, bipolar disorder, and dementia are steadily increasing each year, and alarmingly so in children and young adults. While mental illness is a very real and serious health issue, we are coming to understand that low levels of vitamin B12 can lead to some of the same symptoms as these neurological illnesses. According to Glenn Catalano, MD, a psychiatrist at the University of South Florida College of Medicine, B12 deficiency is a commonly overlooked cause of psychiatric illness, including depression, irritability, anxiety, and dementia. In order to avoid the development of neuropsychiatric symptoms, some experts recommend that B12 levels should be at least 600 pg/mL, and over 1,000 pg/mL to maximize mental functioning.³⁸

References available upon request