Vitamin B12 Deficiency



Vitamin B12 deficiency and Alzheimer's Disease 

Many studies have linked low vitamin B12 levels with Alzheimer's Disease, and studies on the brains of people as they age have shown a steady decline in levels of vitamin B12 in the brain.

Alzheimer's Disease and its relationship with dementia 

Alzheimer's Disease is the most common form of dementia amongst older people. The disease affects parts of the brain that affect memory and speech. Over 1% of the population is affected with Alzheimer's disease. Diagnosis of AD is hard and the symptoms generally only occur after there has been extensive neurological damage.  As the disease progresses there is a progressive decline in memory and cognitive capacity in affected individuals. As the disease progresses their is an increasing build up of neurofibrillary tangles, which can be detected by Magnetic Resonance Imaging (MRI). Progression of the disease can be measured by a decreased cognitive capacity, which can be assessed via a Mini-Mental State Examination (MMSE).

Possible causes of Alzheimer's Disease 

Whilst the exact cause of Alzheimer's disease is not known there are a number of observations that suggest that the cause of the Alzheimer's Disease may be largely due to a combination of micro-nutrient deficiency.

Selenium Deficiency

Selenoproteins are important for normal brain function, and it has been shown that a deficiency in function of these proteins can lead to impaired cognitive function and neurological disorders. Selenium is an important co-factor for the formation of active vitamin B2 (FAD/FMN) and also in the action of glutathione peroxidase. Examination of the serum of persons with AD has shown a significantly reduced level of selenium.

Iron Deficiency

Iron is a critical factor in the oxidation:reduction reactions carried out not only in heme proteins such as haemoglobin and myoglobulin,  but also in the formation of critical iron-sulphur complexes in the mitochondrial proteins aconitase, and the cytochromes I, II and IV in the electron transport chain. Studies comparing AD patients with age-matched controls have shown a significant decrease in the levels of serum iron, ferritin (the iron storage protein) and transferrin (the iron transport protein).

Vitamin B12 Deficiency

Vitamin B12 is an essential vitamin involved in the development and maintenance of the neuronal myelin sheath, and vitamin B12 deficiency is known to be associated with signs of demyelination. Several studies have shown significantly lower levels of vitamin B12 in the serum of individuals with AD. Examination of brain slices of the frontal lobe has shown a greatly reduced quantity of vitamin B12 in the ageing brain, particularly in the level of methyl B12. Intravenous injection of methyl-B12 was shown to improve intellectual functions such as memory, communication and emotional function in patients with Alzheimer-type dementia.

Acetyl Choline Deficiency

Decreased levels of acetyl choline and cholinergic receptors are found in the brains of persons with AD (Lane etal,2006). Choline can be obtained either from dietary  lecithin or by methylation of phosphatidylethanolamine, to generate phosphatidyl choline (an important brain lipid) and then removal of the phosphatidyl group to yield choline. Supplementation with choline has been shown to increase cognition in animal models of AD (Yan etal, 2014). Decreased levels of phosphatidylcholine has been found in the brains of persons with AD (Gaudin et al, 2012) and in the RBCs of AD patients (Selley, 2007). Apart from its role as a neurotransmitter, acetylcholine also functions as a potent vasodilator (Lin etal, 2013). Lack of acetylcholine and NOS is thought to be important factors in the reduced cerebral blood flow, which is a feature of AD (Lin etal, 2013).

Elevated Homocysteine

Many studies have associated elevated homocysteine levels and significantly lower Mini-Mental State Examination stores in AD. The two main nutrient deficiencies associated with elevation in homocysteine are deficiencies in vitamin B12 (particularly methyl B12) and folate (or more specifically 6-methyl tetrahydrofolate). Initially it was thought that the simple deficiency in either vitamin was the cause of the homocysteine reduction, however, an alternative explanation for elevated homocysteine is possible. Thus, when homocysteine is produced it has three potential fates. First it can combine with methyl-B12 and through the action of methionine synthase the homocysteine is converted to methionine. Methyl-B12 is then regenerated through the action of 5-MTHF, Co(I)B12 and methionine synthase to form THF and Methyl B12. Second, homocysteine can receive the methyl group from tri-methyl glycine (betaine) through reaction with betaine-hydroxmethyl transferase (BHMT), thereby forming methionine and dimethylglycine. More commonly though, a third mechanism is employed to remove homocysteine. In this reaction, homocysteine is complexed to serine via the action of cystathionine-beta synthase (CBS), to form cystathionine, which can then be used in the formation of cysteine, hydrogen sulphide (H2S) and in the generation of free sulphur for the formation of iron-sulphur proteins such as aconitase, and the cytochromes of the electron transport chain. The action of CBS is dependent upon both heme and the active form of vitamin B6, pyridoxal phosphate. In the event that CBS activity is reduced one would expect a concomitant drop in the activity of aconitase and reduced formation of H2S. Zhang and co-workers (2016)have shown that elevation of homocysteine, as seen in autism, schizophrenia and ageing is associated with a drop in the levels of cystathionine in the brain.

Reduced Aconitase activity in Alzheimer's Disease

The iron-sulphur protein, Aconitase is a very important enzyme whose major function is in the conversion of citric acid to aconitic acid, at the start of the citric acid cycle. Reduced activity of aconitase can be measured by a build up in the levels of citric acid. A block at this stage in CAC effectively means that the potential energy production (as measure by molecules of ATP produced) gained from the metabolism of glucose is reduced from 36 molecules of ATP per molecule of glucose to only 2 molecules of ATP per molecule of glucose. Mangialasche and co-workers (2015) have shown a direct relationship between decreased activity of  aconitase in individuals with mild cognitive impairment and those with Alzheimer's disease and reduced MMSE scores., that was further reduced  studies have associated elevated homocysteine levels and significantly lower MMSE total score.

Reduced hydrogen sulfide levels in Alzheimer's Disease

Apart from the generation of free sulphur for the formation of iron-sulphur proteins, such as aconitase, CBS is also involved in the production of free hydrogen sulfide (H2S) from cysteine. H2S has been shown to act as both a neurotransmitter in the brain, but also a smooth muscle relaxant. Eko and co-workers (2002) have shown that the levels of brain H2S are greatly reduced in the brains of AD patients. By analogy with the drop in aconitase activity in elevated homocysteine, one would also expect their to be a drop in H2S production in elevated homocysteine. Apart from its role as a neurotransmitter, hydrogen sulfide has also been shown to inhibit amyloid plague formation (a feature of AD)(Rosario-Alomar etal, 2015; Liu etal, 2015), to be involved in brain remodelling (Kamat et al), and to inhibit neuroinflammation (Kida and Ichinose, 2015). .

Reduced nitric oxide levels in Alzheimer's Disease

One critically important enzyme involved in vasodilation is the enzyme nitric oxide synthase, which functions by producing nitric oxide, which induces vasodilation. A possible consequence of NO production has been the association of NO production and improved learning and memory (Paul and Ekambaram, 2011). In addition, lack of NS activity has been shown to contribute to increased oxidant stress and endothelial dysfunction in cerebral microvessels (Santhanam et al, 2015; Austin etal, 2010. Furthermore is has been found that there is lower expression of endothelial NOS in AD brain lesions (Jeynes and Provias, 2009).

Single nutrient deficiency as the causative agent in Alzheimer's Disease

Whilst it is most likely that multiple nutrient deficiencies combine to produce the progressive disease that is Alzheimer's Disease, there is also the possibility that a single nutrient deficiency can initiate the cascade of conditions outlined above. This nutrient is vitamin B2, or more correctly the biologically active enzyme co-factor, flavin adenosine dinucleotide (FAD).

Deficiency in functional vitamin B2 can occur due to low dietary intake of dairy produce, low dietary intake of selenium (an element that is low in many countries through out the world), or low intake of iodine (quite common in people avoiding adding salt to their cooking). Overt hypothyroidism is common in AD.

FAD sufficiency is required for more than 100 enzymes in the body, but two in particular have consequences on vitamin B12 and folate. Deficiency of activity of the FAD-dependent enzyme Methionine synthase reductase eventually leads to a deficiency in vitamin B12, and more particularly methyl-B12. Deficiency in B12 in turn leads to deficiency in folate for the folate cycle as B12 is required to process 5MTHF, the more common form of folate in the diet. Lack of B12 has been show to result in low intracellular folate. Deficiency of FAD further compounds folate cycling as the enzyme MTHFR, cannot move folate out of the folate cycle into the methylation cycle, thus further reducing the regeneration of methyl B12 following donation of the methyl group to homocysteine to regenerate methione. Reduced levels of methyl B12 and folate have both been implicated in the development of elevated homocysteine. The reduced level of methyl B12 will in turn reduce the production of SAM, and thereby reduce Choline phosphatidyl choline, acetyl choline. Futher, low levels of B12 are also associated with thinning of the myelin sheath, and myelin thickness has been found to be very reduced in the brains of people with AD.

Low levels of intracellular folate can in turn lead to reduced production guanosine, a precursor in the synthesis of tetrahydrobiopterin (BH4), an essential co-factor for phenylalanine hydroxylase, tyrosine hydroxylase, phenylalanine hydroxylase and NOS. The combined lack of FAD and BH4 will greatly reduce the activity of NOS, and lower the production of NO, increasing blood pressure and reducing vascular dilation in the brain. reduced activity of NOS, reduced production of serotonin, reduced production of dopamine, nor-epinephrine, epinephrine, melatonin, adrenalin.

FMN, the other active form of vitamin B2,  is also required as a co-factor for the enzyme Pyridoxine-5-phosphate, the enzyme that produces pyridoxal phosphate from pyridoxic acid. Hence low functional vitamin B2 will also lead to reduced activity of P5P dependent enzymes, such as cystathionine beta synthase. In addition, FAD is intimately involved in processing of iron, initially in the uptake from the intestine, but also in the formation of the porphyrin ring via the enzyme protoporphyrinogen IX oxidase. Hence deficiency of FAD will ultimately lead to loss of iron (from uptake) and retention of iron due to lack of formation of the porphyrin ring and subsequent production of heme. Lower production of both P5P and heme will lead to lower function of the enzyme cystathoinine beta synthase (CBS).

Iron Precipitation and Parkinson's Disease: Parkinson's disease is characterized by two main features, the lack of production of DOPA by the enzyme tyrosine hydroxylase, and precipitation of iron within dopamine producing cells. Iron is normally bound within tyrosine hydroxylase via two Histidine molecules and a glutamate residue. A feature of the iron is that it must be in the ferrous (Fe++) state for activity. In conditions of low glutathione concentrations and a more oxidizing environment, one would expect that ferrous iron would be rapidly oxidized to ferric (Fe+++) iron, which would not be available for the formation of active tyrosine hydroxylase. This situation would be exacerbated in conditions of low functional vitamin B2 because the enzyme glutathione reductase, which is dependent upon FAD for activity would also have reduced activity. Notably, glutathione depletion in the substantia nigra is one of the earliest biochemical events reported in PD. Such depletion has been found to be associated with a reduction in the activity of a specific enyzme, Glutathione-dependent oxidoreductasae. Functionally this results in decreased formation of iron-sulphur (Fe-S) proteins, particularly aconitase and succinate dehydrogenase, both of which are essential components of the Krebs cycle (Lee etal, 2009). A reduction in the levels of glutathione is a consequence of vitamin B12 deficiency. In cases of functional B2 deficiency, the situation would be exacerbated due to the oxidation of GSH to GSSG, which could not then be reduced by glutathione reductase, as it is an FAD-dependent enzyme.

Potential Treatment of Alzheimer's disease


By the time a patient develops Alzheimer's disease, there has been significant damage to the neurones and vitamin B12 is severely depleted in the liver, but more importantly in the brain and CSF. Accompanying the deficiency of B12, there is also a reduced level of ferritin.

Whilst it is relatively easy to increase the levels of iron, and to introduce vitamin B2, iodine and selenium, standard supplements containing vitamin B12 are not effective in increasing the serum and CSF levels of vitamin B12 and so constant prolonged  high dose administration of vitamin B12 is required. Studies have shown that at least with dementia progression can largely be halted by such treatment. In addition studies using high dose methylcobalamin concluded that high dose methylcobalamin is a safe and effective treatment for psychiatric disorders in patients with Alzheimer-type dementia*. These workers stressed that high levels of methylcobalamin had to be reached in the CNS. Such levels are not achievable with high dose oral supplements++. A topical form of vitamin B12 has recently been developed that is a specially formulated preparation that is an easy to apply, needle-free delivery system to the skin of the Alzheimer's disease patient, and which has the potential to provide high doses of VB12 to the AD patient without the use of needles**. This pain-free form of delivery greatly increases the patient comfort experienced during the administration of the medication and allows for self-medication without the need for medical staff or any special training. It has recently become apparent that oral supplementation with vitamin B12 does not provide enough vitamin B12 to overcome vitamin B12 deficiency due to the limited uptake capacity of the intestine for vitamin B12, hence there is a requirement for higher initial doses of vitamin B12 to be supplied either by injection or via the topical vitamin B12 formulation.  In addition, the topical formulation of vitamin B12 is particularly suited to patients who may have gastro-intestinal problems, such as gastric ulcers, atrophic gastritis, Crohn’s Disease and Ulcerative Colitis, or who are on Metformin™ medication, which can often lead to vitamin B12 deficiency.   


Further Information on Vitamin B12 and Alzheimer's Disease


* Ikea etal, 1992

++Mitsuyama etal, 1988

A site for self assessment can be found at 

Check out the following sites for further information on Alzheimer's Disease

Lee etal, 2009 A disruption in Iron-Sulfur center biogenesis via inhibition of mitochondrial dithiol glutaredoxin 2... Antiox Redox Sig. 11, 2083-2094PMC 2819798

Supplemental scientific references on vitamin B12 and Alzheimer's Disease

Supplemental scientific references on vitamin B12 and Dementia




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The statements on this site compose a compendium of generally recognized signs of vitamin B12 deficiency, and problems that can then ensue They also are formulated from a summary of relevant scientific publications. In addition they may contain some forward looking statements of a general nature.
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