Vitamin B12 : tips for family physicians

NOTE and DISCLAIMER:

This article is for general interest of qualified family physicians only. It is NOT for their diagnostic or therapeutic use.

It is definitely NOT for any public use whatever, nor intended in any way to be taken as advice for any medical or health condition.

Marginal vitamin B12 deficiency may be seen in vegetarians and the elderly.
It should be taken seriously, as it has clinical consequences.

Vitamin B12 is one of the more interesting nutrients in medicine. Although it has generally been thought that B12 deficiency is relatively rare and mainly found in cases of pernicious anaemia, it is also a well documented fact that family physicians give more B12 injections than almost any other vitamin supplements and this seems to be the case in many countries around the world.

The patient group to whom these injections are most often given is the elderly, and the indication usually such vague complaints as tiredness. Many high minded articles have been written cricitising this practice, which is generally portrayed as unscientific hogwash, based on anecdotal effects for a common and non-specific complaints.

New evidence

But the wheel is slowly turning for vitamin B12. For a start, it is important to know that, however high minded the criticism of family physician practice, the value of giving B12 for tiredness has never really been scientifically disproved. In fact there have been only two small studies that I am aware of, neither of which could be said to have discredited the anecdotal evidence. In one, vitamin B12 supplementation was given to patients with low serum B12 levels and the effects on tiredness noted. The results were positive, but so was the effect of placebo, with no significant difference between the two [Ref.1]. In a second study, however, the results were more positive: in a small sample of patients who complained of tiredness but had normal serum B12 levels, B12 supplements produced improvement in tiredness and well being significantly greater than placebo [Ref.2].

Marginal deficiency

In recent years a growing body of evidence has begun to show that marginal vitamin B12 deficiency is indeed a common problem, particularly amongst the elderly. In an ambulant elderly population in New Zealand, for example, nearly 20% had sub-normal serum B12 levels [Ref.3]. It also is becoming clearer that this condition can have clinical consequences. Recent studies have linked marginal B12 deficiency to abnormalities in immune response and neurological function, even without any changes in the blood count. Another important study published last year found significant changes in more sensitive metabolic indicators of B12 status when patients with `normal' B12 levels were given B12 supplements, suggesting that so-called `normal' serum B12 levels may not be so normal after all [Ref.4].

The family physician's perspective

What does this all mean to the family physician? Firstly that, whilst the traditional risk factors for B12 deficiency are still valid (vegetarianism, pernicious anaemia, gastric atrophy, gastric or small bowel resection etc.), the elderly are another risk group to seriously consider. The reasons for this are not entirely clear, but seem to be related to malabsorption. This may be due to a mild gastric atrophy in a section of the population genetically predisposed to it. Symptoms which could arouse your suspicions might include: tiredness, impaired immunity, mild dementia and any peripheral neuropathic symptoms.

In considering the differential diagnosis of mild dementia, it has been clearly shown that B12 deficiency can cause CNS damage without there being any macrocytosis or anaemia in the blood count. However, the important clue in such cases is that there is often some subtle degree of peripheral neurological defect or symptomatology and this usually can be elicited by careful history and examination if the patient is able to cooperate. As far as confirming the situation in the laboratory, the situation at present is currently somewhat in flux. There is a red cell B12 assay available, but the place of this assay is not as clear cut as it is, for example for red cell folate. It is clear that levels of serum B12 which would previously have been thought of as borderline to low normal must be treated with some degree of suspicion where the clinical picture warrants it. More sensitive metabolic tests such as methylmalonic acid excretion are available, but not in common use, particularly amongst family physicians. However, these tests may well become more widely used in the near future.

Vegetarians

As far as vegetarians are concerned, there have also been a few common misconceptions about their vitamin B12 levels which need to be laid to rest. It has conventionally been said that the body has enough B12 in its liver stores to last at least 2 years. Hence B12 deficiency in vegetarianism, even strict vegans, is unlikely in the early phases of their dietary habit. However, in practice the relation between intake and serum levels is subject to a good deal of individual variability. I have personally seen vegetarians with low B12 levels after only 6 months of vegetarian practice. It is important to routinely check B12 levels in vegetarians. This particularly applies to women of childbearing age, since low B12 in a pregnant woman can be associated with neurological damage in the newborn.

Practice tips
  • Think of marginal B12 deficiency in any elderly patient with dementia, peripheral neurological symptoms or impaired immunity.

  • Check serum B12 levels routinely in all vegetarians.

  • Marginal serum B12 levels should be taken seriously.

References:

  1. Br Med J 1970 2:458-60
  2. Br J Nutr 1973:30:277-283
  3. NZ Med J 1989;102:402-4
  4. Lancet 1995;346:85-89

    Some material on the Internet

    Vitamin B12 deficiency: haematological findings
    Vegetarian Pages

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