Vitamin B12 Deficiency
Deficiency of vitamin B12 is one of the commoner deficiencies encountered in general practice. Severe deficiency can result in the picture of pernicious anaemia with a mixture of neurological changes and severe anaemia, which prior to the discovery of its treatment by the administration of raw liver sandwiches and a high red meat diet, resulted in serious disability and death.
Nowadays regular use of specialised oral supplements or injections of vitamin B12 will treat or prevent deficiency completely. Mild deficiency can still cause neurological impairment and may be missed if not assessed carefully. In addition there is real concern that the imminent fortification of some foods with folic acid as has been proposed by the Food Standards Agency [link FSA] will result in delayed recognition of vitamin B12 deficiency by many doctors.
Folic acid from foods, fortified foods and supplements will treat the haematological changes but not the neurological and mental ones which are often not reversible and thus the appearance of this deficiency will be masked and diagnosis and treatment may be delayed.
Prevalence of Vitamin B12 Deficiency
|Vitamin B12 Deficiency
Plasma B12 <118pmol/l
MCV > 101fl
Causes of Vitamin B 12 Deficiency
The main causes of vitamin B 12 deficiency are:
- Poor dietary intake – vegan or poor quality vegetarian diet
- Failure to absorb food-derived vitamin B12 as a result of declining acid production by the stomach in those aged >50 years
- Pernicious anaemia – specific antibodies that interfere with vitamin B12 absorption
- Following bowel surgery with loss of either the stomach, gastric bypass or resection of the distal part of the small bowel
- Bowel disease – coeliac disease, Crohn’s and bacterial bowel overgrowth
- Pancreatic disease
- Drug-induced – omeprazole, metformin, colchicine, neomycin and nitrous oxide
- Genetic disorders of transcobalamin II a transport protein in the blood
The commonest cause in the general population would appear to be a relative failure to absorb food-derived vitamin B12 probably due to the natural decline in acid production by the stomach with increasing age. As a result mild vitamin B12 deficiency develops often without anaemia but with fatigue and other symptoms. As a result of this common situation in the US the Institute of Medicine of the National Academies now recommends that all aged over 50 years take a supplement or consume food that has been fortified with crystalline vitamin B12.
Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic acid, Biotin and Choline. 1998. http://books.nap.edu/openbook.php?record_id=6015&page=R1
Important Facts about Vitamin B12 Deficiency and its Treatment
- Early symptoms of deficiency include: fatigue, weight loss, a sore painful tongue, poor concentration, mood change, loss of sensation in the feet, loss of balance when the eyes are closed or in the dark and difficulty walking
- A macrocytic anaemia may develop but often not until late in the disease and only in a minority
- Despite this the guidelines from NICE, National Centre for Health and Clinical Excellence, for the assessment and treatment of Chronic Fatigue Syndrome, CFS/ME, specifically advise against measuring serum vitamin B12 unless the patient is anaemic. www.nice.org.uk/CG53
- Treatment of deficiency typically involves injections of relatively large doses of vitamin B12 1000ug, 1mg, in the form of hydroxycobalamin alternate days in those with neurological involvement and every 2 to 4 days in those without. Usually after 6 injections the frequency can be reduced to once every 2 to 3 months. However in those with neurological involvement alternate day injections may need to be continued until there is no further improvement
- Well absorbed oral preparations of vitamin B12 can now sometimes be used as an alternative to vitamin B12 injections and both haematological and neurological response may be a s good with oral as with injection. However these later may still be preferred in the initial correction of severe deficiency and may be a more reliable form of treatment in the very elderly and those who are forgetful or unable to regularly take their medication. www.cochrane.org/reviews/en/ab004655.html
- If anaemia is present in an individual who is at risk of potassium deficiency due to weight loss, poor muscle bulk or use of diuretic medication the effect of the initial vitamin B12 injections can be to stimulate a marked production of red blood cells which greatly increases the demand for potassium and can precipitate a deficiency. Pre-treatment with potassium supplements, and a potassium rich diet (fruit and vegetables, especially bananas and potatoes) is advisable.
- Mild vitamin B12 deficiency (<133 pmol/l) was found in 13% of free-living elderly aged >75 years living in the region of Banbury, Oxford, England. Low levels of vitamin B12 were associated with an increase in the risk of cognitive decline and a small increase in the risk of peripheral nerve damage in the lower limbs as evidenced by an absent ankle jerk. Whilst some of the decline may be part of ageing some may be due to lack of vitamin B12 and possibly other nutrients and thus may be prove to be preventable.
Hin H et al. Clinical relevance of low serum vitamin B12 concentrations in older people: the Banbury vitamin B12 study. Age and Ageing. 2006; 35(4):416-422