The Definitive Manual on Vitamin B12
It’s the stuff of spy movies. When about to be caught, with no way out, the spy bites on a cyanide pill, causing death to come quickly. Yet despite its toxicity, cyanide is found in most vitamin B12 supplements on the market today!
It’s a tiny amount, won’t cause any harm, and superior forms are available, so don’t let that put you off taking supplements. B12 has a boatload of functions, is needed by every cell, and plays crucial roles in many body processes.
Despite its importance, deficiency is surprisingly common, not just among those on plant-based diets but even among meat eaters, for reasons we’ll explain.
What’s shocking is that the medical authorities still have out-of-date views on what B12 deficiency looks like, so many people remain undiagnosed, leaving them at risk of irreversible harm and without hope of recovery.
It’s vital to understand the importance of B12 and the symptoms of deficiency so you can take charge of your health and aren’t failed by the medical system.
Overview
- Vitamin B12 plays crucial roles in many cellular functions, including producing healthy blood cells, DNA synthesis, energy production, and more. Untreated deficiencies can lead to severe health problems, while improving insufficient levels of B12 can increase energy, improve the functioning of the nervous system, support brain health, and help prevent heart disease.
- B12 deficiency is widespread and mostly undetected. It can occur at any age but is more prevalent in seniors, even among meat eaters, because its absorption and utilization by body cells is a multistep, delicate, and complex process that’s easily disrupted.
- Blood tests used to detect deficiency are unreliable, and experts consider the cut-off point to provide a diagnosis too low. This means many people with B12 deficiency remain untreated, risking their health.
What is Vitamin B12?

Vitamin B12 is an essential nutrient that can’t be made by the body so must come from the diet.
It’s one of eight members of the vitamin B group, which are all water soluble, allowing them to dissolve in water, travel through the bloodstream and be peed out of the body if there’s too much in the blood.
Not only is B12 the largest and most chemically complex of all vitamins, but it’s unique because it’s joined to a metal – cobalt, which is why B12 is also called cobalamin. In the body B12 appears in the active chemical form of methylcobalamin-- the methylated form-- or adenosylcobalamin. More on the different forms in a minute...
B12 is needed by every cell in the body and plays crucial roles in a vast number of cellular functions. It’s involved in the manufacture and normal functioning of blood cells, DNA formation, gene expression, nerve function, energy production, toxin removal, the metabolism of lipids (fats) and the production of the essential amino acid, methionine.
It’s essential for healthy nerves and glands, digestion, cognition and mood, blood formation, immunity, skin and mucous membranes, bones, and pregnancy. In other words, there’s almost no aspect of the body that doesn’t need B12 to function normally.
Let’s look at the role of B12 in more detail.
Health Benefits of Vitamin B12
Improves Energy and Endurance
In the form of adenosylcobalamin, B12 is needed by the mitochondria, the cell’s major energy producers. Any shortfall can cause fatigue, low energy, lethargy and exhaustion.
Historically, before B12 was discovered, severe deficiency showed up as a blood disorder where red blood cells don’t form properly. They become distorted and enlarged (megaloblastic anemia) and this was given the name, pernicious anemia. These impaired blood cells had reduced ability to carry oxygen leading to the typical symptoms of anemia which includes weakness and fatigue.
Today, megaloblastic anemia is differentiated from pernicious anemia. The former can be caused by any of many conditions that disrupt B12 absorption, whereas the latter is an autoimmune disease.
In the pernicious form the body either attacks its own stomach cells to prevent B12 being separated from food, or it attacks cells that secrete intrinsic factor - a sugar/protein molecule produced by the stomach that’s needed for B12 absorption. Pernicious anemia is usually seen in older people but there’s also a juvenile form affecting children under ten.
Since fatigue is an early symptom of B12 deficiency, if diagnosed and B12 is supplemented, fatigue lessens in a day or so and general tiredness lifts after a few weeks after which energy and endurance are restored.
Encourages Nervous System Health
The nervous system needs B12 to function normally. It’s used to produce fatty acids that are incorporated into the myelin sheath that surrounds nerves. A damaged myelin sheath will disrupt and impair signaling between brain cells. B12 is also needed to produce proteins and neurotransmitters in the central and peripheral nervous system.
According to the late Dr. Joseph Chandy, a British general practitioner (primary care physician) and B12 specialist, “neurological and neuropsychiatric signs and symptoms are the most frequently encountered presentations of vitamin B12 deficiency today” and are seen in three-quarters of patients with B12 deficiency. [1]
If left untreated, and severe deficiency develops, it can cause a devastating condition called sub-acute combined degeneration of the spinal cord (SACD). Symptoms include tingling and numbness, weak limbs, difficulty walking, vision problems, depression, low attention span and memory loss.
Anemia doesn’t always accompany SACD and since physicians rely on blood tests for B12 deficiency and signs of anemia, the condition is often misdiagnosed as chronic fatigue syndrome (CFS), myalgic encephalomyelitis (ME) and especially multiple sclerosis (MS), which has a very similar set of symptoms.
In fact, a recent study described a novel molecular link between vitamin B12 and MS that takes place in specialized brain cells called astrocytes. The authors recommend supplementing B12 to nourish these cells. [2]
Dr. Chandy helped many people misdiagnosed with such conditions regain their health. One was a patient who had trouble walking, often needing to use a mobility scooter, until she took B12.
Another was a 17-year-old with aches and pains all over the body and dependent on crutches or a wheelchair. After her neurologist dismissed her as an attention-seeker and thought the condition was all in her mind, she consulted Dr. Chandy who diagnosed B12 deficiency. After one month the pain had greatly diminished and she was able to walk without crutches.
Promotes a Sharper, Clearer Memory

B12 is vitally important to the health of the brain with deficiency causing a wide range of neuropsychiatric symptoms. Anemia itself, whether caused by B12 deficiency or for other reasons, puts people, especially seniors, at greater risk of dementia.
Over a century ago, nervous and mental symptoms were linked to pernicious anemia and in 1988 researchers reported that 28% of 141 consecutive patients with B12 deficiency - yet without anemia or any red blood cell anomalies - had neurological symptoms. [3] That bears repeating: The science shows that you don't have to be anemic to experience the negative effects of B12 deficiency.
And according to the Institute of Medicine, 75%–90% of people with clinically relevant B12 deficiency have neurological disorders that include dementia. In fact, there are many similarities between dementia and B12 deficiency. Both:
- increase with age
- affect the central nervous system
- promote inflammation
- have a genetic component in many instances
- cause loss of short-term memory, impaired cognitive function and confusion
The kind of symptoms seen with B12 deficiency are confusion, fogginess, irritability, apathy, depression, psychosis, impaired judgment, memory loss, mild cognitive impairment and dementia.
Not only can deficiency cause brain dysfunction but also brain shrinkage and structural damage, leading German scientists to urge clinicians “to accurately diagnose and treat early vitamin B12 deficiency to prevent irreversible structural brain damage.” [4]
An international research team found B12 levels in the brains of otherwise healthy people aged 61 to 80 were only a third as much as seen in younger adults. This means age-related cognitive and memory decline could be linked to poor uptake of B12 in some cases.
Richard Deth, who led the team said: "These are particularly significant findings because the differences we found in brain B12 with [normal] aging…are not seen in the blood, which is where B12 levels are usually measured." [5]
One reason low B12 and dementia are linked is because deficiency leads to excess homocysteine.
Essential to Lower Homocysteine
Homocysteine is an amino acid made from the essential amino acid methionine which we ingest from foods containing protein. Without enough B12, homocysteine rises too high, and this negatively impacts brain function.
In 2018 a team of expert scientists produced a paper called “Homocysteine and Dementia: An International Consensus Statement.” In it they wrote that elevated homocysteine is a risk factor for cognitive decline, dementia, and Alzheimer’s disease.
“Intervention trials in elderly with cognitive impairment” they wrote, “show that homocysteine-lowering treatment with B vitamins markedly slows the rate of whole and regional brain atrophy and also slows cognitive decline.” [6]
Nutrients that lower homocysteine are mainly vitamin B12 and B9 (folate) with the help of vitamin B6, so if we want to keep our minds sharp and memories unfaltering, this is one simple strategy for doing so.
B12 and homocysteine are also linked to heart and circulatory disorders.
Supports a Healthy Heart

The American Heart Association accepts that excess homocysteine is linked to a greater risk of stroke and other blood vessel disorders.
A study that pooled the results of twelve previous studies involving over 23,000 adults found that as homocysteine levels rose so did the risk of cardiovascular death. Compared to adults with the lowest levels of homocysteine, those with the highest levels, had a 68% increased risk of death from cardiovascular disease. [7]
In a recently published study containing 5,200 participants, scientists reported “solid evidence” that heart disease mortality increases in line with rising homocysteine levels. [8]
One would think supplementing with B12 and other B vitamins would therefore lower the risk, yet most intervention trials found that while supplementation reduced the risk of stroke by a small amount, it didn’t reduce the risk of a heart attack. The reason for this was suggested in a recent scientific review. Researchers pointed to the “substantial limitations” in trials assessing B vitamins and their role in heart disease prevention and treatment.
In the scientists’ assessment, B vitamins had their greatest cardiac benefit in people with normal kidney function, without unstable angina, and who haven’t had a type of heart attack called non-ST-elevation. So while B12, folate and B6 will help the vast majority of people, their research suggests those with these complaints may not experience dramatic benefits [9]
The role of B12 goes beyond its effect on homocysteine. It’s necessary for various metabolic processes and contributes to DNA synthesis. If these are disrupted because B12 is in short supply, cardiovascular diseases and other illnesses can result.
So, what can you do?
Increasing Your Intake of Vitamin B12
Food Sources
Vitamin B12 doesn't come from food exactly. Believe it or not, vitamin B12 is made by microbes in the digestive tract of animals and then distributed throughout the animal's tissues. That's why meat is the main source of vitamin B12. However, those on a plant based diet can also obtain B12 from fortified foods. For example:
Animal sources:
- Meats of all kinds
- Liver
- Fish
- Shellfish
- Eggs
- Milk
- Yogurt
- Cheese
Plant sources:
- Seaweed – some species
- Silk® organic unsweet soymilk
- Fortified breakfast cereals
- Fortified nutritional yeast
- Fortified soy products
- Enriched plant milks
Dietary Supplements

Since B12 plays so many essential roles in the brain and body, many people choose to take B12 supplements. This is especially important for those of us who eat only plant foods.
In fact, the Vegan Society recommends eating either fortified foods two or three times a day, or taking a one a day vitamin B12 supplement providing at least 10 micrograms or a weekly vitamin B12 supplement providing at least 2000 micrograms. [10] You can also self-administer vitamin B12 shots with the help of a functional medical doctor.
Forms of Vitamin B12
When you're shopping for vitamin B12 supplements, you'll encounter two main categories:
- Nature's Own: These are the ready-to-use forms your body prefers - methylcobalamin and adenosylcobalamin. Think of them as pre-assembled furniture, ready to be placed in your home immediately.
- Lab-Created Helpers: Then there are cyanocobalamin and hydroxocobalamin. These are synthetic versions, like flat-pack furniture that needs some assembly. Once inside your body, these forms undergo a transformation process, eventually becoming the same active forms as their natural counterparts.
Both types can support your B12 needs, but they take slightly different routes to get there. The natural forms are immediately recognized and put to work, while the synthetic forms require a bit of processing by your body first.
Cyanocobalamin
Cyanocobalamin combines cobalamin with cyanide and is the cheapest form of B12. Uptake isn’t optimal as it’s lost from the body very quickly. This is because the body recognizes cyanide as a poison and rapidly excretes it through the kidneys, so you won’t be harmed from taking B12 in this synthetic form. In fact, in cases of cyanide poisoning, cobalamin is used to flush it out of the body!
Even so, cyanocobalamin can cause mild headaches and some people just don’t benefit from it. For these reasons Dr. Chandy didn’t recommend taking B12 in this form but as either of the active forms or as hydroxocobalamin which converts more easily into the active forms.
Methylcobalamin
Picture methylcobalamin as the VIP guest at your body's nutrient party. This form of B12 doesn't need a special invitation or to change outfits - it's ready to mingle with your cells right away. Unlike its synthetic cousin cyan