Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency

BACKGROUND

Vitamin B12 deficiency is common and rises with age. Most people with vitamin B12 deficiency are treated in primary care with intramuscular vitamin B12 which is a considerable source of work for health care professionals. Several case control and case series studies have reported equal efficacy of oral administration of vitamin B12 but it is rarely prescribed in this form, other than in Sweden and Canada. Doctors may not be prescribing oral formulations because they are unaware of this option or have concerns regarding effectiveness.

OBJECTIVES

To assess the effectiveness of oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency.

SEARCH STRATEGY

Searches were undertaken of The Cochrane Library, MEDLINE, EMBASE and Lilacs in early 2005. The bibliographies of all relevant papers identified using this strategy were searched. In addition we contacted authors of relevant identified studies and Vitamin B12 research and pharmaceutical companies to enquire about other published or unpublished studies and ongoing trials.

SELECTION CRITERIA

Randomised controlled trials (RCTs) examining the use of oral or intramuscular vitamin B12 to treat vitamin B12 deficiency.

DATA COLLECTION AND ANALYSIS

All abstracts or titles identified by the electronic searches were independently scrutinised by two reviewers. When a difference between reviewers arose, we obtained and reviewed a hard copy of the papers and made decisions by consensus. We obtained a copy of all pre-selected papers and two researchers independently extracted the data from these studies using piloted data extraction forms. The whole group checked whether inclusion and exclusion criteria were met, and disagreement was decided by consensus. The methodological quality of the included studies was independently assessed by two researchers and disagreements were brought back to the whole group and resolved by consensus.

MAIN RESULTS

Two RCT's comparing oral with intramuscular administration of vitamin B12 met our inclusion criteria. The trials recruited a total of 108 participants and followed up 93 of these from 90 days to four months. High oral doses of B12 (1000 mcg and 2000 mcg) were as effective as intramuscular administration in achieving haematological and neurological responses.

AUTHORS' CONCLUSIONS

The evidence derived from these limited studies suggests that 2000 mcg doses of oral vitamin B12 daily and 1000 mcg doses initially daily and thereafter weekly and then monthly may be as effective as intramuscular administration in obtaining short term haematological and neurological responses in vitamin B12 deficient patients.

Absence of macrocytic anaemia in Alzheimer's disease

There is an association between Alzheimer's disease (AD) and low serum levels of vitamin B12 and folic acid. Patients also have elevated serum levels of homocysteine and disease progression might therefore be associated with the development of a macrocytic anaemia. We investigated the relationship between disease duration, homocysteine and haematological indices in patients with clinically diagnosed AD and healthy elderly controls. Haemoglobin and platelet counts fell only slightly with increasing dementia duration, but there were no other changes in haematological indices. In particular, macrocytosis and red cell distribution width were unrelated to disease duration and no patients were anaemic. Our results support previous observations that the neurological and haematological features of B12 and folate deficiency are often unrelated in these patients.

Transcobalamin polymorphism and serum holo-transcobalamin in relation to Alzheimer's disease

Isoforms of the vitamin B(12) carrier protein transcobalamin (TC) might influence its cellular availability and contribute to the association between disrupted single-carbon metabolism and Alzheimer's disease (AD). We therefore investigated the relationships between the TC 776C>G (Pro259Arg) genetic polymorphism, total serum cobalamin and holo-TC levels, and disease onset in 70 patients with clinically diagnosed AD and 74 healthy elderly controls. TC 776C>G polymorphism was also determined for 94 histopathologically confirmed AD patients and 107 controls. Serum holo-TC levels were significantly higher in TC 776C homozygotes (p = 0.04). Kaplan-Meier survival functions differed between homozygous genotypes (Cox's F-Test F(42, 46) = 2.1; p = 0.008) and between 776C homozygotes and heterozygotes (Cox's F test F(46, 108) = 1.7; p = 0.02). Proportionately fewer TC 776C homozygotes appear to develop AD at any given age, but this will require confirmation in a longitudinal study.

Functional vitamin B(12) deficiency and Alzheimer disease

Moderately elevated total serum homocysteine is associated with an increased risk of atherothrombotic vascular events. Accordingly, serum homocysteine is increased in patients with vascular dementia but is also increased in clinically diagnosed and histologically confirmed AD. It is generally considered that homocysteine potentiates endothelial and neuronal oxidative injury in these diseases. A complementary model of oxidative stress-induced hyperhomocystinemia is proposed by the authors. The hypothesis accounts for several unusual features relating to single-carbon metabolism and AD, including the absence of macrocytic anemia in these patients. It is suggested that cerebral oxidative stress augments the oxidation of an intermediate form of vitamin B(12) (cob[I]alamin) generated in the methionine synthase reaction, thereby impairing the metabolism of homocysteine. Oxidative stress also compromises the intraneuronal reduction of the vitamin to its metabolically active state. Currently available pharmaceutic forms of vitamin B(12) are unlikely to be utilized by neurons under these conditions. Glutathionylcobalamin might be preferential for the treatment of such patients.

Homocysteine and cognitive decline in healthy elderly

Serum homocysteine is increased, and correlates inversely with cognitive scores, in Alzheimer's disease (AD), vascular dementia and "age-associated memory impairment". Elevated levels might signal accelerated cognitive decline, although this remains to be established. We therefore repeated Mini-Mental State Examinations, together with additional ADAS-Cog assessments, in 32 healthy elderly individuals to determine whether prior homocysteine levels predicted cognitive changes over a 5-year period. Homocysteine predicted follow-up cognitive scores and rate of decline in cognitive performance independently of age, sex, education, renal function, vitamin B status, smoking and hypertension (p < 0.001). Homocysteine predicted word recall (p = 0.01), orientation (p = 0.02) and constructional praxis scores (p < 0.0001). One subject, with the second highest initial homocysteine, had developed probable AD at follow-up. Fasting total serum homocysteine appears to be an independent predictor of cognitive decline in healthy elderly and exerts a maximal effect on spatial copying skills.

Analogues, ageing and aberrant assimilation of vitamin B12 in Alzheimer's disease

Vitamin B12 assimilation might be disrupted in patients with Alzheimer's disease. We therefore measured B12 carrier protein saturation and inactive B12 'analogues' in patients compared with healthy elderly individuals in a prospective case-controlled survey. Twenty-three patients, aged 60 or over, with features compatible with DSM-IV criteria for primary degenerative dementia of the Alzheimer type were recruited together with 18 cognitively intact age-matched control subjects. Total vitamin B12 (active corrinoids), holo- and apo-haptocorrin and transcobalamin were measured in serum. B12 analogues (inactive corrinoids) were estimated from the difference between R-binder-determined corrinoids and an intrinsic factor based B12 assay. Alzheimer patients had significantly lower active corrinoid than control subjects and the analogue/corrinoid ratio was significantly higher in the Alzheimer group. The inter-relationship between age, analogues and transcobalamin polarised patients into two distinct groups. Two disparate mechanisms might exist for the development of cerebral B12 deficiency in Alzheimer's disease, although both imply a disruption of selective B12 assimilation and analogue elimination in such patients.

Total serum homocysteine in senile dementia of Alzheimer type

OBJECTIVE

The main hypothesis was that subtle vitamin B12 deficiencies occur more commonly in senile dementia of Alzheimer type (SDAT) that in healthy elderly individuals, and may be revealed by elevated total serum homocysteine (tHcy). A subsidiary hypothesis was that such deficiencies would be nutritionally independent as determined by retinol binding protein (RBP).

DESIGN

A prospective case-controlled survey.

SETTING

A Welsh urban psychogeriatric assessment centre and local general practice.

PATIENTS

Thirty patients, aged 65 or over, seen consecutively in 1994 with features compatible with DSM-III-R criteria for primary degenerative dementia of Alzheimer type and 30 cognitively intact age-matched control subjects.

MEASURES

Diagnosis was assessed using the CAMDEX. Cognitive scores were evaluated with the CAMCOG scale for patients and MMSE scores for control subjects. THcy was measured using high performance liquid chromatography (HPLC), and RBP assayed by a radial immunodiffusion method.

RESULTS

Patients had a highly significant elevation of tHcy compared with control (p < 0.0001). Multiple regression highlighted the interrelated effects of tHcy and total serum cobalamin on cognitive scores. RBP did not differ between groups. Macrocytosis was absent, and neutrophil hypersegmentation uncommon, in hyperhomocysteinaemic patients.

CONCLUSIONS

SDAT patients have significantly elevated tHcy. This is independent of RBP determined nutritional status. 'Classical' haematological changes of cobalamin or folate deficiency are poor predictors of tHcy in these patients. Aberrant cobalamin tissue delivery appears to contribute to SDAT cognitive decline. Relative contributions of other tHcy determinants require further investigation.

Trypsin inhibition: a potential cause of cobalamin deficiency common to the pathogenesis of Alzheimer-type dementia and AIDS dementia complex?

There is increasing evidence for an association between Alzheimer-type dementia (AD) and nutritionally independent cobalamin deficiency. Furthermore, low serum cobalamin values occur in a kindred with familial Alzheimer's disease (FAD) and histopathological confirmation of AD neuropathology. The Cobalamin deficiency could be either a consequence or cause of amyloidogenesis. Cobalamin deficiency is also associated with the acquired immunodeficiency syndrome (AIDS). A common pathogenic mechanism may exist for AIDS dementia complex (ADC) and AD, but there is no explanation at present for these associations. This paper presents the hypothesis that protease inhibition is a common factor in AD and ADC resulting in protein-bound cobalamin malabsorption and disrupted cobalamin metabolism.

Familial Alzheimer's disease and vitamin B12 deficiency

A kindred with autosomal dominant familial Alzheimer's disease in which a mutation results in a valine to glycine substitution at amyloid precursor protein codon 717 has recently been described. Individuals in this pedigree were studied retrospectively and prospectively, to evaluate the relationship, if any, between Alzheimer's disease and vitamin B12 deficiency. The presence of Alzheimer's disease was found to be associated with lower serum vitamin B12 values compared with unaffected family members. There were no significant differences between macrocytosis, the presence of anaemia, serum folate or red cell folate between affected and unaffected family members. The implications of this finding are discussed with regard to previous descriptions of an association, and in relation to the clinical features of this particular kindred.

Familial Alzheimer's disease. A pedigree with a mis-sense mutation in the amyloid precursor protein gene (amyloid precursor protein 717 valine-->glycine)

Ten affected individuals are described from a kindred with autosomal dominant familial Alzheimer's disease in which a mutation in the amyloid precursor protein gene results in a valine to glycine substitution at amyloid precursor protein 717 which co-segregates with the disease. The mean age at onset of symptoms was 52 years with a range from 40 years to 67 years. The median duration of the disease was 11 years, with a range of 7-16 years. All individuals fulfilled the National Institute for Neurological and Communicative Disorders and Stroke criteria for probable Alzheimer's disease. A homogeneous clinical and neuropsychological pattern was evident within the family. Myoclonic jerks, seizures, depression and a lack of insight were common features. Positron emission tomography demonstrated biparietal bitemporal hypometabolism in the one affected individual who was studied. The diagnosis was confirmed histopathologically in one individual.

Alzheimer's Disease: A ‘cobalaminergic’ hypothesis

An association between Alzheimer's Disease (AD) and low CSF and serum vitamin B12 (B12) has recently been described (1, 2, 3). This is apparently independent of nutritional intake (4). It has been suggested that such patients may exhibit an atypical form of cobalamin deficiency (3, 4). It is therefore proposed that these deficiencies may be aetiologically important, at least in sub-groups of AD, and a mechanism is described whereby B12 deficiency may result in the characteristic neurotransmitter changes of the disease. The hypothesis generates predictions regarding biochemical evaluation of such patients and suggests associations between the neurochemical disturbances and structural abnormalities of AD.