Vitamin B12 deficiency: Neither fish nor fowl

5. February 2015
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It is a known fact that many older people suffer from vitamin B12 deficiency. Nonetheless this vitamin deficiency is something to which attention should be paid when thinking about younger people as well. Particularly at risk are vegans and vegetarians. In addition, every third or fourth blood test gives a false normal result.

In cases where patients show unexplained neurological disorders, a vitamin B12 deficiency should be taken into consideration as a potential cause. This is because the typical neurological symptoms – such as paraesthesia, pallor, fatigue, difficulty in concentrating, memory impairment and depression – are not always accompanied by the classic megaloblastic anaemia of vitamin B12 deficiency. And only in the late stages of vitamin B12 deficiency does the full clinical picture of funicularmyelosis make its appearance.

Vitamin B12 (cobalamin) is essential for blood formation, cell division and functioning of the nervous system. The German Society for Nutrition, to choose an example, recommends an intake of 3 micrograms per day; other countries take a slightly less demanding stance with their recommendations. Older people and pregnant women do however have higher vitamin B12 needs. The highest vitamin B12 content are contained in animal products, most notably meat, fish, dairy products and eggs.

90 Percent of vegans have vitamin B12 deficiency

The body’s storage of vitamin B12 – up to 2 mg in the liver and another 2 mg in other organs – in the instance of complete abstinence lasts for about three years. Nevertheless, many more people are suffering from vitamin B12 deficiency than previously thought. In a study published in November 2014 Flavia Fayet-Moore and colleagues studied vitamin B12 intake for 308 healthy Australian female students aged 18 to 35 years. The study reveals that 11.3% of the women studied showed an abnormally low vitamin B12 concentration of less than 120 pmol/l in the blood. If the limit is instead set to 185 pmol/l, the number of women affected rises to 42.1%. In addition, 4.7% of the women showed an elevated value of greater than 0.34 μmol/l for methylmalonic acid, a functional indicator of the vitamin B12 supply. The reason for this is probably changing eating habits, more and more people are dieting or refrain entirely from eating meat or any animal products.

A case example from Germany: “The daily intake of vitamin B12 here is on average about 5 micrograms”, explains Prof. Claus Leitzmann, Emeritus nutritionist at the University of Giessen, Germany. Nevertheless, many groups of people are affected by vitamin B12 deficiency. Vegans in particular are at risk: “We have in one study found 70 percent of vegetarians and 90 percent of vegans to have vitamin B12 deficiency”, reports Prof. Rima Obeid of the University Hospital of Saarbrücken. Plant products contain vitamin B12 only in exceptional cases; most vegan products are therefore not suitable to ensure a sufficient intake of vitamin B12. Accordingly, ovo-lacto vegetarians are less at risk of suffering a Vitamin B12 deficiency if they eat eggs and dairy products regularly.

Ill despite adequate vitamin B12 intake

Vitamin B12 deficiency can also be caused by certain diseases. A deficit of intrinsic factor which is crucial for the absorption of vitamin B12, caused for example by chronic gastritis (initiated by the formation of autoantibodies against parietal cells or intrinsic factor), or brought about by a gastric resection. What’s more the terminal ileum may be impaired in its function, for example by a resection or through inflammatory bowel diseases such as Crohn’s disease.

Yet medications can also have a negative effect on the vitamin B12 provision: this is precisely what two independently published studies in June show, in that metformin, taken by patients suffering from type 2 diabetes mellitus or polycystic ovary syndrome, leads to a statistically significant reduction of the vitamin B12 levels in the blood, and that the extent of reduction is dependent on the dose of metformin as administered. In addition, medications used for inhibition of gastric acid secretion, for example proton pump inhibitors and H2 blockers, cause a vitamin B12 deficiency, as Lam and colleagues show in a study from 2013.

Controversy over the correct vitamin B12 test

Vitamin B12 is present in the blood in two forms: bound to transcobalamin (TC) or bound to haptocorrin (holohaptocorrin). The form bound to TC (holotranscobalamin: Holo-TC) represents the metabolically active form of vitamin B12. This form however accounts for only about 20% of the vitamin B12 quantity, the remaining 80% being present as holohaptocorrin. Although there assays do exist which can distinguish between these two forms, often for cost reasons only the total vitamin B12 level is determined – a normal value is considered to be 150-800 pmol/l.

However, the accuracy of these tests is controversial: the authors Carmel and Agrawal already found in a study published in 2012 that the immunoassays tested (competitive-binding luminescence-based assays: CBLAs) in 22 to 35% of cases yielded a false-negative result. In this case the main problem appears to be the presence of intrinsic-factor autoantibodies in serum, which interfere with the assay antibody. A Roche Diagnostics-funded study  on the other hand could not find any evidence that Roche’s CBLA system (Elecsys®) leads to false-negative results.

In view of these results, the experts agree that only a determination of the holo-TC value is really meaningful: “Only the Holo-TC reveals how much usable vitamin B12 is available to the body’s cells”, emphasises Prof. Obeid. She explains: “In comparison to any costs emerging from the (potential) consequences, the expense of the approximately 50 Euro Holo-TC determination test is not significant”.

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2 comments:

Dr. Robert Goodbary Robert Goodbary
Dr. Robert Goodbary Robert Goodbary

what is the normal dose of injectable vit. B-12. How many cc’s or M.L.

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Mrs Jenny O’Neill
Mrs Jenny O’Neill

I wonder if there is any genetic or familial link – I would be interested to know

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