By Kirstie Vesseur, Registered Clinical Nutritionist (CNA), Legacy Nutrition, NZ and Australia.
Your hands tingle when you wake up. You sleep and still feel flat. You walk into a room and forget why, and your mood is lower than it should be for the life you have. These can all be quiet signs of low B12.
I see low B12 often in clinic, and it is not always in the woman you would expect. It shows up in meat eaters as well as vegetarians, because the problem is often absorption rather than intake. Here is what drives it, what to test and what actually helps.
What B12 does, and how low B12 shows up
Vitamin B12 is needed for:
making healthy red blood cells
protecting nerves (it helps maintain the myelin coating)
making DNA
methylation, a chemical process your body uses to make brain chemicals and process hormones
When B12 runs low, symptoms can creep in slowly over months or years: fatigue, pins and needles, poor memory and concentration, low mood, a sore or smooth tongue, and in more advanced cases, anaemia or balance problems. Nerve symptoms can appear even when your blood count looks normal.
Why is my B12 low? Common causes
Not enough in your diet
B12 is found reliably only in animal foods: meat, fish, shellfish, eggs and dairy. Seaweed, spirulina and fermented foods are not dependable sources. If you are vegan, B12 from a supplement or fortified foods is essential. Vegetarians who eat some eggs and dairy can still fall short.
Your liver stores B12 for several years, so a low intake can take a long time to show up on a blood test.
Low stomach acid or low intrinsic factor
To absorb B12 from food, you need stomach acid to release it, and a protein called intrinsic factor, made in the stomach, to carry it into the body. Absorption can drop with:
Pernicious anaemia, an autoimmune condition where the immune system targets the stomach cells that make intrinsic factor. It is more common in women and after 50, and more likely if you already have an autoimmune condition such as autoimmune thyroid disease (Hashimoto's).
H. pylori infection or long-term inflammation of the stomach lining (atrophic gastritis).
Low stomach acid, which is more common in older adults, mostly because of atrophic gastritis, H. pylori and long-term acid-reducing medicines.
Medications
Some common medications are known to lower B12 over time:
Metformin, prescribed for type 2 diabetes and sometimes for insulin resistance and PCOS (now also called PMOS). New Zealand metformin data sheets advise checking B12 at least yearly in people taking it long term.
Acid-reducing medications such as PPIs (for example, omeprazole) used long term.
Please do not stop or change these. If you take them, ask your GP whether regular B12 monitoring makes sense for you.
Gut conditions
B12 is absorbed at the far end of the small intestine (the ileum). Coeliac disease, Crohn's disease affecting the ileum, bowel surgery and SIBO (where bacteria use up B12 before you can) can all lower your levels. If you have ongoing gut symptoms, my article Why Am I Always Bloated? is a good next read.
Higher demand
Pregnancy and breastfeeding increase your needs. If you are vegan and pregnant or breastfeeding, talk to your midwife or GP about B12, because babies of mothers with low B12 are at risk of deficiency too. Regular heavy drinking can also lower B12 status.
What a standard test can miss
Serum B12 is the usual blood test, and it is a reasonable starting point. But most of the B12 it measures is bound to a carrier protein your cells cannot use. That means a result in the "normal" range does not always rule out a problem, especially if it sits near the lower end and you have symptoms.
Tests worth discussing with your GP include:
Active B12 (holotranscobalamin): the portion your cells can take up and use.
Homocysteine: often rises when B12 or folate is low. Raised levels are also linked with cardiovascular risk, although lowering homocysteine with B vitamins has not been shown to prevent heart disease.
Methylmalonic acid (MMA): rises when B12 is low at the cell level, though it is not always easy to access.
Intrinsic factor antibodies: to check for pernicious anaemia. A negative result does not fully rule it out. Parietal cell antibodies are sometimes tested too, but they are less specific.
Full blood count: large red blood cells can be a clue.
A note on folate: high doses of folic acid can correct the anaemia caused by low B12 without fixing the nerve effects, which can hide a deficiency. This is one reason I always look at B12 and folate together. If you are planning a pregnancy, my article on methylfolate vs folic acid explains how the two work together. Low B12 also often sits alongside low iron, so it is worth reading Why Is My Ferritin Low? if you are tired all the time.
What to eat for healthy B12
Adult women need about 2.4 mcg of B12 a day, rising to 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding. Approximate amounts in common foods:
Beef liver: about 70 mcg in 85 g cooked. A small serve once a week goes a long way.
Clams, mussels and oysters: some of the richest sources of all. A serve of green-lipped mussels is an easy NZ option.
Salmon: about 2.6 mcg in an 85 g fillet.
Beef mince: about 2.4 mcg in 85 g cooked.
Milk: about 1.3 mcg in a glass (around 250 ml).
Eggs: about 0.5 mcg each.
As an example, two eggs at breakfast, a salmon fillet at dinner and a glass of milk gives you roughly 5 mcg, about double the daily target. If you are plant based, choose B12-fortified foods and plan on a supplement. For easy high-protein meals built around these foods, have a look at Legacy's Kitchen.
Supplements: form and dose
Which form?
Cyanocobalamin, methylcobalamin and hydroxocobalamin all work. Cyanocobalamin is the most studied, and there is no good evidence that one oral form is better than another, so choose the one that suits you and your budget.
How much?
To correct a low level when your GP agrees oral B12 is suitable: guidelines commonly use at least 1,000 mcg (1 mg) a day when absorption is the problem. Your GP will advise on dose and how long to take it. Oral doses of 1,000 to 2,000 mcg a day raised blood levels about as well as injections in a Cochrane review, although the evidence is limited.
If you eat no animal foods: take a daily B12 supplement or use fortified foods every day. No upper limit has been set for B12 in New Zealand or Australia because it has low toxicity.
Injections: if you have pernicious anaemia, injections are usually needed for life. If you have nerve symptoms such as numbness, tingling or balance problems, treatment starts with injections. In New Zealand, hydroxocobalamin injections are funded and arranged through your GP (usual GP or nurse fees may apply).
Ideally get tested before you start, as supplementing first can make your results harder to interpret. Check with your GP or pharmacist if you take medication, are pregnant or breastfeeding.
Treat the cause
If H. pylori, coeliac disease or SIBO is part of the picture, treating the cause is what helps keep levels up over the long term. Studies show B12 levels tend to rise after H. pylori is treated. Your GP can test for both H. pylori and coeliac disease.
Frequently asked questions
What is the difference between serum B12 and active B12?
Serum B12 measures all the B12 in your blood. Active B12 measures only the fraction your cells can take up and use. It is possible to have a normal serum result while active B12 is low, so active B12 can add useful detail when symptoms do not match your results.
Can low B12 affect my mood?
It can. B12 is involved in making brain chemicals and protecting nerves, and low B12 has been linked with low mood and depression in research. Correcting a deficiency can help, but low mood usually has more than one cause, so please also talk to your GP. If you are struggling or having thoughts of harming yourself, contact your GP, or call or text 1737 any time to talk to a trained counsellor in New Zealand. In Australia, call Lifeline on 13 11 14.
How quickly will I feel better?
Many people start to feel better within a few weeks of treatment, though it can take up to three months. Tell your GP if you feel worse. Nerve symptoms such as tingling can take several months or longer to improve, and may not fully resolve if they have been there a long time. This is why it pays to find low B12 early.
Where to start
If you have symptoms that fit, or you have been supplementing without feeling much difference, it is worth looking at why your B12 is low in the first place. My free Check Your Bloods page is a good place to start.
Want help with this one-on-one? See how I work with women on DNA-based nutrition (nutrigenomics), or browse all my services.
This article is general education, not personal medical advice. Please talk with your GP before starting supplements or changing medication.
References
National Institute for Health and Care Excellence (NICE). Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). 2024. https://www.nice.org.uk/guidance/ng239
Wang H, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database of Systematic Reviews. 2018. https://www.cochrane.org/CD004655
NIH Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Accessed 2026. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
NHMRC. Nutrient Reference Values for Australia and New Zealand: Vitamin B12. Accessed 2026. https://www.eatforhealth.gov.au/node/87
Medsafe. Metformin (Mylan) New Zealand data sheet. Accessed 2026. https://www.medsafe.govt.nz/profs/Datasheet/m/metforminmylantab.pdf
Pharmac. Hydroxocobalamin injection: medicine notice. Accessed 2026. https://pharmac.govt.nz/medicine-funding-and-supply/medicine-notices/hydroxocobalamin
Healthify He Puna Waiora. Pernicious anaemia. Accessed 2026. https://healthify.nz/health-a-z/p/pernicious-anaemia
