News reports surrounding the tragic death of a university student, where Vitamin B12 deficiency has been discussed as a possible contributing factor, have brought this often-overlooked nutrient into the spotlight.
For many people, Vitamin B12 deficiency seems like a simple issue. If you eat animal products, surely you are getting enough. If you are vegan or vegetarian, perhaps you need a supplement.
But in nutritional medicine, the story is rarely that straightforward. Unfortunately, we see B12 deficiencies/insufficiencies becoming more common, especially in children who are labelled as ‘picky eaters’ and yet parents are unaware.
We all love a bullet point summary
- Vitamin B12 deficiency is not just a vegan or vegetarian issue.
- Meat-eaters can also become deficient due to poor digestion, low stomach acid, gut dysfunction, medications, autoimmune conditions, or genetic differences.
- Symptoms may include fatigue, brain fog, memory problems, pins and needles, numbness, low mood, poor concentration, dizziness, and neurological changes.
- A ‘normal’ blood B12 result does not always mean your cells have enough B12.
- Functional markers such as Active B12, Methylmalonic Acid (MMA), and Homocysteine can provide additional insight into how B12 is being utilised within the body.
- Vitamin B12 works closely with folate, vitamin B6, iron, and healthy methylationMethylation is one of the body's most important ‘behind-the-scenes’ processes. Happening millions of times every second, it helps regulate everything from energy production and hormone balance to detoxification, neurotransmitters, DNA repair, and how we respond to stress. Yes, it is literally involves in every reaction in your body. At its heart, methylation is the process of transferring tiny chemical tags, called methyl groups (one carbon with 3 hydrogens if you like a bit of chemistry), from one molecule to another. To do this efficiently, the body relies on nutrients such as folate, vitamin B12, vitamin B6, zinc, choline, methionine and more. Together, these nutrients help produce a molecule called SAMe, which acts as one of the body's main methyl donors. pathways.
- Nutritional Therapists often look at patterns across multiple markers rather than relying on a single laboratory result.
What is on your plate is only one piece of the puzzle
Vitamin B12 deficiency can affect vegans, vegetarians, meat-eaters, young adults, older adults, and people who believe they are eating a healthy diet. The reason is quite simple, obtaining B12 and using B12 are two very different things.
At the New School of Nutritional Medicine, B12 is one of the many examples we use to teach students the concept of biochemical individuality. Two people can eat the same foods, have similar blood test results, and yet experience very different levels of cellular nutrient sufficiency.
Understanding Vitamin B12 requires us to look beyond food and into digestion, absorption, genetics, transport systems, cellular function, and the interconnected nature of human physiology.
Why is vitamin B12 so important?
Vitamin B12 plays a critical role throughout the body. It is involved in:
- Energy production
- Nervous system function
- DNA synthesis
- Red blood cell formation
- Methylation pathways
- Neurotransmitter production
- Myelin sheath maintenance
The myelin sheath acts like insulation around nerve cells, helping messages travel efficiently throughout the nervous system. When B12 becomes insufficient, nerve communication can begin to suffer.
B12 is also required for healthy methylation pathways, biochemical reactions involved in producing neurotransmitters such as serotonin, dopamine and melatonin. When these pathways are compromised, symptoms may extend beyond fatigue and affect mood, cognition, sleep and neurological function.
The symptoms often develop slowly
One reason B12 deficiency can be difficult to recognise is that the liver stores several years’ worth of Vitamin B12. As a result, symptoms may develop gradually. Early signs may include:
- Fatigue
- Brain fog
- Difficulty concentrating
- Word-finding difficulties
- Memory lapses
- Pins and needles
- A sore or unusually red tongue
As deficiency progresses, symptoms may become more severe:
- Muscle weakness
- Persistent numbness
- Balance problems
- Dizziness
- Mood changes
- Depression
- Cognitive decline
In severe cases, profound neurological and psychiatric symptoms can develop. Historically, severe B12 deficiency was associated with a condition sometimes referred to as “megaloblastic madness”, where neurological dysfunction led to paranoia, hallucinations, confusion and symptoms that could resemble dementia.
Why do people become deficient/insufficient?
Most assume B12 deficiency is simply caused by not eating enough animal products. While diet can certainly play a role, it is far from the only reason. Here are some factors that can be playing a vital role in B12 deficiency/insufficiency
1. Reduced dietary intake
Vitamin B12 is found predominantly in animal foods such as:
- Meat
- Fish
- Eggs
- Dairy products
People following vegan diets are at increased risk unless they consume fortified foods or supplements.
2. Low stomach acid
The absorption of B12 begins in the stomach. Stomach acid is required to release B12 from food proteinsProtein is one of the three main macronutrients, alongside fats and carbohydrates, yet for many years it was often the forgotten member of the trio. More recently, protein has become something of a celebrity in the nutrition world, appearing in everything from snack bars and cereals to coffee and desserts. Whilst the marketing can sometimes get a little carried away, the truth is that protein is essential for human health. Every cell in the body relies on it. Protein helps build and repair tissues, supports immune function, forms enzymes and hormones, transports nutrients, and helps maintain muscle mass, particularly as we age. before it can be absorbed further down the digestive tract. Factors that may reduce stomach acid include:
- Ageing
- Long-term stress
- Proton pump inhibitor medications
- H2 blockers
- Gastritis
3. Pernicious anaemia
Pernicious anaemia occurs when the immune system attacks the stomach cells that produce intrinsic factor, a protein required for B12 absorption. Without an intrinsic factor, B12 absorption becomes severely impaired regardless of dietary intake.
4. Gut dysfunction
The gut plays a major role in nutrient absorption. Conditions that may impair B12 status include:
- Coeliac disease
- Crohn’s disease
- Small intestinal bacterial overgrowth (SIBO)
- Chronic gut inflammation
- Previous bowel surgery
This is one reason why nutritional therapists often investigate digestive health when B12 deficiency is suspected.
5. Medications 
Certain medications may interfere with B12 absorption or metabolismMetabolism is not a calorie-burning furnace that sits somewhere near your belly button, deciding whether you can fit into last year's jeans. Metabolism is the set of chemical processes taking place inside your body every second of every day, keeping you alive., including:
- Metformin
- Proton pump inhibitors
- H2 blockers
6. Genetic differences
Not everyone handles nutrients in the same way. One genetic variation that has received attention is the FUT2 gene. FUT2 influences what is known as secretor status and affects interactions between the gut lining and the microbiomeWhen you hear the word microbiome, you probably think of the gut. Fair enough, it gets most of the attention. But what if we told you that microbes are not just hanging out 'down under'? They are everywhere. There is the oral microbiome living in your mouth, the skin microbiome covering every inch of your body, the urogenital microbiome, the lung microbiome, and, of course, the celebrity of the microbial world, the gut microbiome. These tiny organisms are not unwanted guests infact, truth be known, we are their guests. They are part of you, which helps keep you alive.. Research suggests that some FUT2 variants may influence circulating B12 levels.
Interestingly, some individuals may have apparently ‘good’ B12 blood levels yet still experience symptoms of poor cellular utilisation. Looking at a single marker in isolation can sometimes be misleading, and genetics also matters.
When a normal B12 blood test misses the ‘mark’
One of the most important concepts we teach at the New School is that laboratory interpretation is about patterns, not individual numbers. A standard NHS B12 test measures total B12.
However, B12 travels through the bloodstream attached to transport proteins. Much of the measured B12 is bound to a protein called haptocorrin and is not immediately available for cellular use. A smaller proportion is bound to transcobalamin, forming active B12 (transcobalamin + B12 equals holotranscobalamin), which can be delivered into cells.
This means a person may have, normal serum B12 or high serum B12 or even borderline serum B12 while still experiencing a functional or cellular deficiency. Having B12 circulating in the bloodstream is not the same as successfully delivering it into cells where it is needed.
The functional nutrition approach
Rather than asking: “Is the B12 normal?” A functional nutrition practitioner does not only ask ‘Are the B12 levels normal?’ They are more likely to ask:
- Is the nutrient available?
- Is it being transported correctly?
- Is it entering the cells?
- Is it performing its functions?
- Is there evidence of tissue response?
To answer these questions, several markers may be evaluated together.
Serum B12: Provides information about the amount of B12 circulating in the bloodstream.
Active B12 (holotranscobalamin): Measures the fraction of B12 available for delivery into cells.
Methylmalonic Acid (MMA): One of the most useful functional markers of cellular B12 status. When B12-dependent pathways are not functioning efficiently, MMA tends to rise. This is particularly important because MMA may reveal cellular deficiency even when serum B12 appears adequate.
Homocysteine: Elevated homocysteine may indicate difficulties in methylation pathways involving vitamin B12, folate and vitamin B6.
Folate: Folate works closely alongside B12. A deficiency in one nutrient can sometimes influence the interpretation of another.
Iron markers: Iron and B12 are both involved in healthy red blood cell production. Deficiencies in either nutrient may contribute to fatigue, poor concentration and reduced energy.
Full blood count and red cell indices: Markers such as:
- MCV (Mean Cell Volume)
- MCH (Mean Cell Haemoglobin)
Both can provide clues about how the bone marrow is responding and whether larger-than-normal red blood cells are developing which can be indicative of low B12 (folate could be low too).
Different types of B12 supplements
Not all B12 supplements are the same. The question we ask ‘is the B12 performing it’s function?’ Vitamin B12 can come in different forms, and each form may behave slightly differently in the body.
Methylcobalamin is an active form of B12 involved in methylation pathways. It is often used when supporting homocysteine metabolism, mood, cognition, and nervous system function.
Adenosylcobalamin is another active form of B12, used inside the mitochon
dria, where it supports energy production.
Hydroxocobalamin is a naturally occurring form of B12 that can be converted by the body into the active forms it needs. It is often considered a gentler option and may be useful for people who are sensitive to methylated nutrients.
Cyanocobalamin is a synthetic form of B12 commonly found in cheaper supplements and fortified foods. The body has to convert it into active forms before it can be used.
This is why the “best” B12 supplement is not always the same for everyone. Some people feel better with methylcobalamin, some tolerate hydroxocobalamin better, and others may need a combination of methylcobalamin and adenosylcobalamin.
As always, the form, dose and route of B12 should be considered alongside symptoms, test results, medical history, medications, and the reason the deficiency or insufficiency is there in the first place.
We look for patterns in your story
One of the challenges in modern healthcare is that we often become fixated on individual markers.
We know that the body does not communicate through a single number. It communicates through a whole mind, body-wide ‘web’. A symptom is rarely caused by a single pathway, nutrient deficiency rarely exists in isolation and a laboratory result does not tell the whole story.
The role of nutritional medicine is to understand how physiology, biochemistry, genetics, digestion, lifestyle and environment interact.
This approach to health and wellbeing, allows us to move beyond asking whether a number is inside a reference range and instead ask what the body is doing or rather communicating.
Nutrient deficiency/insufficiency is not about taking this for that
Vitamin B12 deficiency is far more complex than many people realise. It is not simply a vegan issue AND it is not always obvious on routine blood work. It also is not always explained by dietary intake alone.
The recent attention surrounding B12 deficiency serves as an important reminder that symptoms should never be ignored and that nutrient status is influenced by far more than what we eat.
At the New School of Nutritional Medicine, we teach students to recognise patterns, understand physiology, psychology, appreciate biochemical individuality, and most importantly, see the person behind the laboratory results. Ultimately, good healthcare is not about treating ‘blood markers’ or functional testsIf you have ever been told, ‘your blood tests are normal’, not ‘normal’ or not yourself, then you have already discovered one of the reasons functional testing has become so popular. Functional tests are designed to provide additional information about how the body is functioning. They may explore areas such as hormones, digestion, nutrient status, fatty acids, the microbiome, genetics, metabolism, or stress physiology. Think of them as gathering more pieces of the health puzzle, ideally before a dis-ease ‘shows up’. Sadly, most people turn to functional tests, once they have a dis-ease. , but about understanding the human being sitting in front of you.
Most importantly, finding a deficiency is only the beginning. The next question we ask, is ‘why is it there?’
- Is it low intake?
- Poor absorption?
- Low stomach acid?
- Medication use?
- Gut dysfunction?
- Autoimmunity?
- Genetics?
Understanding the reason behind that result is what helps create lasting change.
Could this be the beginning of your next chapter?
If you have found yourself reading this thinking, “Why has nobody ever explained B12 like this before?” then you have just ‘experienced’ nutrition medicine.
At the New School of Nutritional Medicine, we teach you how to understand why something is happening, not simply what suppleme
nt to take. Pernicious anemia is on the rise, and this is an autoimmune condition; taking B12 is vital; however, supporting the whole person and addressing the ‘hypervigilant’ immune system is also crucial.
Whether you are a healthcare practitioner wanting to deepen your knowledge, or someone who has fallen in love with understanding health through the lens of nutrition, functional medicine, and coaching (both psychological and health), start your journey at the New School.
Our new academic year begins on 19th September 2026, and we have a few places remaining. Apply now.
To Health!
