Lax, ägg, mjölk och yoghurt, livsmedel som innehåller vitamin B12

B12 deficiency: the signs, the tests and who actually runs low

In Swedish primary care, a person who books an appointment for tiredness is usually offered one blood test for vitamin B12, reported as S-B12. The value comes back inside the reference interval, the visit ends, and the tiredness is unchanged. The pattern is common enough that the British national guideline warns clinicians not to rule out B12 deficiency on a normal blood count alone, because nerve damage can arrive before the blood count moves.

This article goes through what low B12 looks like, why the signs are easy to misread, how S-B12, homocysteine and methylmalonic acid differ, and who genuinely runs low. It then explains the difference between a treatment dose and the 10 micrograms in a daily supplement. Health Royals makes a daily supplement that contains B12, and that is why we want to be precise about where a daily supplement belongs.

Health Royals Peak Performance, supplement with vitamin D3, K2 as MenaQ7, folate as Quatrefolic and omega-3 from algal oil

B12 at Health Royals

Peak Performance Formula provides 10 µg of vitamin B12 per daily dose as MecobalActive® methylcobalamin, together with 200 µg folate as Quatrefolic® and ten other named components, for everyday intake. Vitamin B12 contributes to the reduction of tiredness and fatigue.

See Peak Performance, multivitamin for women with omega 3

What are the signs of low vitamin B12?

They cluster into three groups, blood, nerves and mucous membranes, and not one of them is specific to B12.

The blood picture is the classic one. Red cells become larger and fewer, which shows up as anaemia with a raised mean cell volume, and the person feels tired, breathless on stairs, dizzy or pale. The Swedish patient information service 1177 lists tiredness, poor concentration, dizziness, breathlessness, palpitations, headache and tinnitus among the common complaints.

The nerve picture matters most, because it can become permanent. It usually starts as pins and needles, numbness and reduced sensation in the feet, and it can move upward. Peripheral neuropathy, visual problems from optic nerve involvement and cognitive difficulty all appear in NICE guideline NG239 as findings that should prompt a test.

The mucous membrane picture is smaller, but people notice it: cracks at the corners of the mouth and a sore or burning tongue, both described by 1177, and glossitis, which is on the NICE list.

Why are the symptoms of B12 deficiency so hard to interpret?

Because every one of them has a dozen other explanations that are statistically more likely.

Tiredness, poor concentration and low mood are where iron deficiency, thyroid disease, sleep apnoea, depression, long-term stress and too little sleep all end up. Numb feet can come from diabetes, alcohol or a trapped nerve. A sore tongue can be a fungal infection or a reaction to toothpaste.

That is why a symptom list is close to useless as a self-test, and why the lists of B12 symptoms online match almost everyone who reads them. We have written separately about how stress physiology, sleep and energy interact, because that pathway explains a great deal of everyday tiredness.

Symptoms decide whether a test is worth taking. They do not decide the answer.

What does the S-B12 test actually measure?

It measures all the B12 circulating in serum, both the fraction your cells can use and the fraction they cannot.

Most circulating B12 is bound to haptocorrin and never reaches the tissues. Only the part bound to transcobalamin, measured as holotranscobalamin or active B12, is available to cells. A reassuring total can therefore sit on top of a poor supply, and a low total can occur in people with no functional problem at all.

In its 2014 guidance on cobalamin and folate disorders, the British Society for Haematology writes that there is no gold standard test to define deficiency, that the clinical picture is the most important factor in assessing results, and that definitive cut-offs are not possible across assay methods. A 2014 BMJ review by Hunt, Harrington and Robinson says the same in one line: there is no ideal test.

NICE accepts either total or active B12 as the first test in adults, and active B12 in pregnancy. It treats a total B12 between 180 and 350 ng/L, in British units, as indeterminate rather than normal: the grey zone that sends people home without an answer. Swedish laboratories report in pmol/L against their own intervals, and your printout has to be read against that range.

What is the difference between S-B12, homocysteine and MMA?

S-B12 and active B12 measure how much vitamin is present. Homocysteine and methylmalonic acid measure whether the vitamin is doing its job.

B12 is a cofactor for two reactions. One converts homocysteine to methionine, the other converts methylmalonyl-CoA to succinyl-CoA. When the supply of B12 inside the cell falls, both substrates accumulate, so plasma homocysteine and serum methylmalonic acid rise. They are called functional markers for that reason.

Methylmalonic acid is the more specific of the two. Homocysteine also rises in folate deficiency, in B6 deficiency, in kidney impairment and with age, which makes it a weaker second-line test, and the haematology guideline says so directly.

The advantage of the functional markers is smaller than the marketing around private blood panels suggests. In a study of 11,833 samples with all four markers measured at once, published in Disease Markers in 2020, Jarquin Campos and colleagues found areas under the curve of 0.92 for holotranscobalamin, 0.91 for methylmalonic acid, 0.90 for total B12 and 0.78 for homocysteine. In men and in women under 50 there was no significant difference between holotranscobalamin, total B12 and methylmalonic acid. Only in women aged 50 and over did holotranscobalamin come out ahead.

The Nordic Nutrition Recommendations 2023 chapter on vitamin B12 states the practical conclusion plainly: all four biomarkers have limitations on their own, and a combination is the most suitable approach.

Which groups actually run low on B12?

Four groups, and they overlap less than people assume: those who eat no animal foods, those whose stomachs no longer absorb it, those on certain long-term medicines, and older adults.

Vitamin B12 is produced by microorganisms and reaches us through animal foods, so a diet with no meat, fish, eggs or dairy supplies almost none. In a review of 18 studies in Nutrition Reviews in 2013, Pawlak and colleagues reported deficiency in 62 percent of pregnant vegetarians, 25 to 86 percent of children, 21 to 41 percent of adolescents and 11 to 90 percent of elderly vegetarians, with higher rates among vegans than among vegetarians.

Absorption is the second route. B12 needs intrinsic factor, made in the stomach lining, to be absorbed in the last part of the small intestine. Autoimmune atrophic gastritis destroys the cells that make it and causes pernicious anaemia; coeliac disease, inflammatory bowel disease and stomach or bowel surgery interfere further down. NICE lists all of these, with a family history of autoimmune disease, among the common risk factors.

Age works through the same mechanism: NNR 2023 names older adults as a risk group because of malabsorption from atrophic gastritis, alongside vegetarians and vegans, infants and young children, and pregnant and lactating women. Average B12 intake in the Nordic countries ranges from 2.9 to 8.9 micrograms per day, but average intake and individual absorption are different questions. We have looked at the Swedish figures in our piece on what the national dietary surveys actually show.

Can medicines cause vitamin B12 deficiency?

Yes, and three are common enough in Sweden to be worth naming. Metformin is the best documented. In the Diabetes Prevention Program Outcomes Study, reported by Aroda and colleagues in 2016, low B12 was more frequent on metformin than on placebo at five years, 4.3 percent against 2.3 percent. Including borderline values, the gap was 19.1 percent against 9.5 percent at five years and 20.3 percent against 15.6 percent at thirteen years, and the authors recommended routine B12 testing on metformin.

Acid suppression is the second. In a case-control study of 25,956 people with B12 deficiency and 184,199 controls in JAMA in 2013, Lam and colleagues found that two years or more of proton pump inhibitors carried an odds ratio of 1.65, and two years or more of H2 receptor antagonists 1.25. That is an association, not a reason to stop a prescribed medicine, and the decision belongs with the prescriber.

Nitrous oxide is the third and the most abrupt. Recreational use oxidises the cobalt atom in cobalamin and inactivates it, producing a functional deficiency with neurological injury. A 2024 review in BMC Neurology notes that a normal B12 level can be found in this syndrome, which is why NICE tells clinicians to use homocysteine or methylmalonic acid, not total B12, in nitrous oxide users. NICE also lists colchicine, topiramate and pregabalin among medicines associated with low B12.

What is the difference between treating a deficiency and taking B12 every day?

A confirmed deficiency is treated in healthcare, with doses and routes decided by a clinician. A daily supplement carries a nutritional amount, chosen to keep an ordinary intake steady. Neither can stand in for the other.

If the problem is an absorption failure such as pernicious anaemia, the intrinsic factor route is gone, and no ordinary supplement restores it. Treatment, whether tablets at doses of a different order or injections that bypass the gut, is set by the clinician who made the diagnosis. For someone whose absorption works but whose intake is thin, a nutritional amount taken daily covers the days the diet gives less, and that is where B12 belongs in a daily supplement.

The form matters as much as the amount. Most supplements use cyanocobalamin, a stable synthetic form that the body converts before use, and it is a serviceable form. Methylcobalamin is one of the two forms the body's own enzymes use, the cofactor for the reaction that turns homocysteine into methionine.

We chose it for that reason. When Health Royals selected the B12 for Peak Performance, we started with the form, the one found in food and used by the enzyme, and then with the raw material: MecobalActive®, a branded methylcobalamin made by HealthTech BioActives in Spain, a specialist ingredient manufacturer with a defined specification for its material. Health Royals works with specialist manufacturers, researchers and supplier networks when raw materials are selected. For us, the ingredient cannot be separated from its source, its manufacturer and the reasoning behind its dose.

The dose is 10 micrograms per daily dose: a nutritional level, deliberately above the 4 microgram reference intake set by EFSA and NNR, and far below anything used as treatment. A higher number is not automatically a better dose. It sits alongside folate as Quatrefolic® 5-MTHF at 200 micrograms for a reason: the two vitamins meet in the same homocysteine reaction, which is why a folate shortfall raises the same marker. For a person who eats little animal food, or who is older and eats less, that level keeps a daily intake steady. For a person with pernicious anaemia, metformin-related malabsorption or nitrous oxide injury, the appointment comes first.

What does the research show?

It is clearest where B12 status is low or borderline.

A 2026 review in Nutrients by Yepes-Calderon and colleagues found that the effects of supplementation showed up in subgroups such as people with raised homocysteine or borderline status.

The Nature Reviews Disease Primers overview by Green and colleagues puts subclinical deficiency at between 2.5 and 26 percent of the population depending on the definition used. That range shows how much the definition, and a proper test, matter.

The same review notes observational associations between higher circulating B12 and increased cancer risk, while stressing that the findings are inconsistent and that reverse causation is a serious confounder. Long-term data on high doses are limited, which is one reason we chose a nutritional level.

The overall picture is clear. Deficiency is real, its risk groups are well defined and its nerve damage can be permanent. The biomarkers work in combination, and an ordinary total B12 performs almost as well as the more expensive markers in most people. Uncertainty about the grey zone is an argument for testing properly, not for ignoring the question.

What should you do if you suspect you have B12 deficiency?

Book an appointment and ask for a test, rather than starting supplements first.

The order matters. Taking B12 before the blood sample can normalise the numbers and hide the picture the clinician needs, and if the problem is an absorption failure, ordinary oral doses will not solve it. 1177 advises contacting a health centre if you suspect anaemia. Numbness, unsteadiness or a change in vision deserve prompt attention.

Tell the clinician whether you eat animal foods, what medicines you take, any stomach or bowel surgery, autoimmune disease in the family and any nitrous oxide use. Those details change which test is ordered and how the result is read.

On intake, the reference points are modest. EFSA set an adequate intake of 4 micrograms per day for adults in 2015, 4.5 micrograms in pregnancy and 5 micrograms during lactation, and NNR 2023 landed on the same 4.0 micrograms per day for adults, with a provisional average requirement of 3.2 micrograms.

Among the authorised health claims for vitamin B12 in Regulation 432/2012, the one relevant here reads: vitamin B12 contributes to the reduction of tiredness and fatigue.

So for a person whose diet or medication makes a shortfall plausible, and whose tests are in order, a daily supplement at a nutritional level is a reasonable part of a plan agreed with a clinician. For a person with a confirmed deficiency, treatment comes first.

Our wellbeing page collects the wider context. Peak Performance contains MecobalActive® methylcobalamin at 10 micrograms per daily dose, alongside folate as Quatrefolic® 5-MTHF at 200 micrograms and ten further named constituents, each amount on the label. We publish the form, the dose and the reasoning behind them. We have done the selection so that you do not have to.

See Peak Performance Formula

Further reading

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