Condition
Functional Medicine for B12 Deficiency
Persistent exhaustion, brain fog, pins and needles or breathlessness can all point towards low vitamin B12, yet many people are told their level is normal and sent away without an explanation. At Mosaic Medical, our functional medicine doctors work with patients across the UK to test B12 properly, find out why it is low, and treat the cause rather than the number alone.
What B12 does, and why deficiency matters
Vitamin B12 is needed to make healthy red blood cells, maintain the protective sheath around your nerves, and run the methylation reactions your body uses to build and repair DNA. Because it touches so many systems, a shortfall can affect your energy, your nervous system and your mood at the same time.
Typical symptoms include:
- Persistent fatigue and weakness
- Brain fog, poor concentration or memory changes
- Pins and needles, numbness or altered sensation in the hands and feet
- Low mood, anxiety or irritability
- Breathlessness, palpitations or pale skin
- Sore tongue, mouth ulcers or altered taste
- Unsteadiness or changes to balance
Symptoms often develop slowly and are easily attributed to stress or ageing, which is one reason deficiency can go unrecognised for years.
Why B12 Deficiency Is Often Missed
A standard serum B12 test measures the total B12 circulating in your blood, including the portion your cells cannot actually use. Someone can sit inside the reference range and still be functionally deficient at a cellular level. That is why we look wider, and why we take symptoms seriously even when a result looks acceptable. Our article on what to do when your tests are normal but you still feel unwell explains the principle. We also had a podcast episode on our channel where 2 of our doctors discuss this here.
Depending on your picture, testing may include:
- Active B12 (holotranscobalamin), which reflects the B12 available to your cells
- Methylmalonic acid and homocysteine, which rise when B12 is functionally low
- Full blood count and red cell indices
- Folate, ferritin and iron studies, which interact closely with B12
- Intrinsic factor and parietal cell antibodies, where pernicious anaemia is suspected
- Coeliac screening, thyroid function and inflammatory markers where relevant
Common Root Causes We Investigate
B12 deficiency is a finding, not a diagnosis. The important question is why your levels have fallen, and the answer shapes your treatment.
- Pernicious anaemia, an autoimmune condition in which the immune system affects the stomach cells that produce intrinsic factor, the protein needed to absorb B12
- Absorption problems linked to gut health, including atrophic gastritis, low stomach acid, coeliac disease, inflammatory bowel disease and SIBO
- Previous gastric or small bowel surgery
- Long-term use of medicines that reduce absorption, including proton pump inhibitors and metformin
- Dietary intake, particularly on vegan or strictly plant-based diets
- Increased demand or depletion, including pregnancy, breastfeeding and alcohol use
- Genetic variations affecting B12 transport and methylation, alongside related nutrients such as thiamine and folate
Our Functional Medicine Approach
Your first appointment is a 90-minute consultation. Your doctor reviews your history in advance, then works through your symptom timeline, diet, medications, gut health and any previous results with you.
- We confirm whether there is a true deficiency using active B12 and functional markers, rather than serum B12 alone
- We look for the underlying cause, including autoimmune, gut and medication-related reasons
- We discuss the treatment options that are appropriate for you, which may involve dietary change, supplementation, or prescribed treatment, and we explain the pros and cons of each
- We address what sits alongside the deficiency, such as iron, folate, thyroid function and gut repair
- We monitor your response and adjust, rather than treating once and discharging you
- Where nutrition is central to your recovery, our registered nutritional therapist works alongside your doctor
What Makes Our Approach Different
- Testing that goes beyond serum B12, so functional deficiency is not missed
- A focus on the cause, not just correcting the number
- GMC-registered doctors who can prescribe and who work alongside your GP
- A whole-picture view that connects B12 with fatigue, gut health and mood
- Clear explanations, so you understand your own results
Online B12 Appointments Across the UK
Every consultation is held by secure video call, so you can work with us wherever you live.
- Your initial consultation lasts 90 minutes, with your history reviewed beforehand
- Blood tests are arranged remotely, using home kits or a local blood draw
- We share findings with your GP so that any ongoing treatment is joined up
- You can read about our doctors on the Meet the Team page, and see fees on our pricing page
FAQs About B12 Deficiency
My GP said my B12 is normal. Can you still help?
Yes. A normal serum B12 does not always rule out a functional deficiency, and we can test active B12 and related markers to get a clearer answer. If your symptoms turn out to have another cause, we will look for that instead.
Do I need to stop supplements before testing?
Supplements can affect results, so we will tell you what to pause and for how long before any test is arranged.
Is pernicious anaemia the same as B12 deficiency?
No. Pernicious anaemia is one cause of B12 deficiency, in which an autoimmune process interferes with absorption. It is confirmed with antibody testing, and it changes how long treatment is needed.
Will I need treatment for life?
It depends on the cause. Deficiency caused by diet can often be corrected and maintained, while absorption problems or pernicious anaemia usually need ongoing treatment. Your doctor will explain what applies to you.
Can you work with my GP?
Yes. We share our findings and recommendations with your GP, and we encourage joined-up care.
Do you offer remote consultations?
Yes. We work virtually with patients throughout the UK.
Does the appointment price include testing?
Testing is personalised and arranged separately. We only recommend tests that will make a genuine difference to your care.
Ready to Find Out What Is Behind Your Symptoms?
We recommend starting with a free discovery call with one of our doctors. You can share your story, ask questions, and decide whether our approach is right for you.