Press releases, taken over by newspapers, as a result of UMCG research1 regarding mortality in combination with high B12 values, have led to a lack of clarity and great commotion among patients. We want to allay the concerns of patients and possibly doctors. We can report the following to patients with a B12 deficiency who take supplements (oral or injections): fear of ‘too high values due to supplementation’ is unfounded. The researchers themselves say in an explanatory newspaper report (which was unfortunately published afterwards):

Question: But does this mean that people with a B12 deficiency, who regularly receive injections with B12, must now stop immediately?

‘No,’ Bakker says, firmly. ‘It still applies that it is good to supplement B12 deficiency if medically necessary.’

For the enthusiast, we dig a little further: How does such news come to us? First of all via Twitter,2  where reference is made to the press release of the UMCG:3 

‘For a long time we thought there was no danger in an overdose of vitamin B12. Researcher José Luis Flores-Guerrero and Professor of Internal Medicine Stephan Bakker are now warning of the health risks of too high a B12 level.’

Overdose is: as ingestion. Mirror is: value. Ingestion mortality has neither been studied nor differentiated. Quote from the UMCG press release:3

‘Until now there were no known adverse effects of excessive doses of vitamin B12.’

‘The researchers at the UMCG warn people who take supplements or receive injections to prevent a vitamin B12 deficiency. Many people believe that there is no danger in overdosing on B12 and assume “the more, the better”. Websites about vitamins and also the Health Council and the Nutrition Center indicate that the chance of adverse effects from too much vitamin B12 is very small. However, the thought “if it doesn’t work, it won’t harm” is no longer tenable with the results of this study, say the researchers.’

Do they mean too high a dose or too high values? Too high a dose suggests: too high intake.

Although no causal relationship has been found and the research says nothing about the mechanisms underlying the relationship found, according to the researchers the results are in any case reason to believe that too much vitamin B12 can be taken and that too high a B12 levels pose health risks.

The researchers do not come up with anything new here: it has long been known that a higher mortality can be present at higher values ​​of B12. But it is caused by the underlying clinical picture. We list a number of studies and articles in which this phenomenon is discussed:

  • ‘The significance of a cobalamin in the blood that is too high’4
  • ‘The pathophysiology of elevated vitamin B12 in clinical practice’5

An online message from RTV-Noord6 had the headline: ‘Signal that the dose of B12 must be maximized.’

But it has never been proven that the intake of B12 without a B12 deficiency leads to higher mortality. All that has been proven is that high B12 levels are linked to all-cause mortality. And that is old news.

Patients with chronic myeloid leukemia, acute promyelocytic leukemia, polycythemia vera and / h hypereosinophilic syndrome, which causes a high level of B12, are not mentioned in the report from the UMCG. Also the patients with elevated haptocorinne or FUT2 mutation (genetic disorders) who have a high B12 level in their blood are not included in the study.

Furthermore, the ‘high B12 value’, what the UMCG is talking about, actually still falls under the ‘normal values’. The plasma concentration from the study has been converted from 229 to 367 pmol / L. Normal reference values ​​in this: 148-650 pmol / L. We regularly encounter these values ​​in patients who have complaints and who have received oral supplementation in case of a previously established B12 deficiency, without these complaints having improved sufficiently. Perhaps this cohort is under-treated?

What we do worry about – and we share that concern with the researchers – is the unbridled increase in (multi) vitamin intake by people who have no deficiencies or complaints, or by whom this has never been studied. This can lead to opposite effects, especially with multivitamins to which folic acid and vitamin B6 have been added: an increased dose of which can lead to toxicity. This is not possible with B12, because this vitamin is cleared renally.


The reporting and presentation of the UMCG research is poorly communicated, namely without references and explanations. The researchers should have communicated better on the tricky subject of B12 deficiency. It has misled many patients with B12 deficiency and unnecessarily frightened or confused them.