Vitamin B 12 deficiency can manifest as broad spectrum of diseases. To one extreme it may present as debilitating brain and spinal cord diseases. And to another extreme it can show up with no more than subtle vague symptoms. But whatever it is, vitamin B 12 deficiency symptoms and signs should never be overlooked.



This deficiency is more common in vegetarians and vegans. Besides it is very often seen in babies who are exclusively breast feeding from strictly vegetarian and vegan mothers. But this doesn’t limit B 12 deficiency to this population only. Anyone can suffer from low vitamin B 12 level and its consequences.

Beneficial gut microflora synthesize some vitamin  b12, and for rest of it human are dependent on food.

 We have drafted a separate article on “food options of vitamin B 12 for vegans, vegetarians and non-vegetarians”. This gives a clear idea on what dietary sources can help to prevent vitamin B 12 deficiency symptoms ( cobalamin deficiency)


Here we have classified vitamin B 12 / cobalamin deficiency into 4 broad categories for easy understanding.



a. Fatigue and weakness

Vitamin B 12 deficiency can present as severe fatigue and weakness. These symptoms are vague and no specific. But bear in mind that, these symptoms can also be sign of any other underlying illness. 

However if persistent fatigue is there, which is still unexplained then vitamin B 12 level must be measured. 

b. Repeated headache

If someone has has low B 12 levels then s/he may present with repeated episodes of severe headache. Moreover vitamin B 12 deficient individuals are more likely to get migraine. 


A study was done on same in 2020 which inferred that headache is the most common symptom of vitamin B 12 deficiency in adolescents.


a. Angular stomatitis, Cheilosis, Cheilitis

Angular stomatitis is a condition when angle of mouth or corner of mouth turn painful, red and cracked. Cheilosis and Cheilitis refer to chapped lips ( inflamed lips ).These are earliest signs of vitamin B 12 deficiency. 

Angular stomatitis in not solely limited to B 12 deficient patients. It can be there in many other ailments as listed below.

  • Other nutritional deficiencies like riboflavin ( vitamin B 2 ) deficiency, Folic acid ( vitamin B 9 ) deficiency, iron deficiency etc.
  • Excessive pooling of saliva 
  • Infections like fungal infection ( Candida ), bacterial infection, herpes etc.
  • Allergy or atopy 
  • Inflammatory disease of gut like IBD and coeliac disease
b. Glossitis

It is a condition of inflammation of tongue. Basically in glossitis tongue will be red, painful and smooth. It incurs burning sensation at times. 

Glossitis is an initial feature of vitamin B 12 deficiency. As such, it is an important clue to its suspicion of cobalamin deficiency at early stage.

Other B complex vitamins cause glossitis as well. 

c. Knuckle and palm hyperpigmentation

Usually vitamin B 12 deficiency is an under diagnosed and under treated condition. 

Knuckle and palm hyperpigmentation is a telltale sign of B 12 deficiency. Thus it helps to pick up on this deficiency. Replenishment of vitamin B 12 reverses pigmentation.


a. Anaemia

Vitamin B 12 is imperative for synthesis of genetic material ( DNA ) of cell. If this vitamin is not sufficient enough then DNA synthesis is hampered. The cell lines hence most commonly affected are RBCs ( Red Blood Cells ).

Thereby vitamin B 12 deficiency causes reduced RBCs. Consequently haemoglobin level of that person drops. This is called anaemia. 

Characteristics of this anaemia is, size of red blood cells are unusually bigger when seen under microscope. Hence this is labelled as macrocyctic anaemia. Macrocytic anemia is also seen in folic acid ( vitamin b 9 ) deficiency.

b. Pancytopenia

Human blood has 3 types of blood cells as specified below.

  • RBC ( Red Blood Cells ) – These contain haemoglobin. Haemoglobin transports oxygen to different parts of body.
  • WBC ( White Blood Cells) – These are fighter cells and protect against germs. 
  • Platelets – These are tiny cells which arrest bleeding.

In very low B 12 symptoms, all 3 cell lines of blood decline in number. This is called as Pancytopenia. The person presents with paleness ( due to anaemia ), infections ( because of reduced WBC ) and bleeding ( owing to low platelet ).

c. Jaundice

Though it is rare, but keep in mind that vitamin B 12 deficiency is one of the causes of jaundice symptoms in newborns or children, especially when jaundice is prolonged and lingers for more than 2 weeks.

Human blood is produced inside bone marrow tissue. In B 12 deficiency, before RBCs mature they die prematurely inside Bone marrow itself. The haemoglobin hence present in RBCs are recycled giving rise to bilirubin or jaundice. 



Vitamin B 12 is needed for maintaining “myelin sheath” around nerve. Myelin is a type of fat that covers nerve fibres. It helps in insulation and fast conduction of nerve signal. In absence of myelin, nerve can not function as intended. 

This manifests as various neurological and psychological symptoms. Very low B 12 symptoms can emerge as any of the following ways.

a. Peripheral neuropathy

Peripheral neuropathy is the most common nerve related vitamin B 12 deficiency sign. Here all 3 types of nerves are affected.



Signs of peripheral neuropathy

Peripheral sensory neuropathy develops as tingling or pin and needle prickling sensation or burning in extremities. This starts from hands and feet and progress to arms and legs. Affected limb seems numb.

When peripheral neuropathy impacts motor nerve, extremities become weak and spastic.

Here there is profuse sweating around hands and feet. There may be intolerance to heat at that particular area too.

Peripheral neuropathy is symmetrical in vitamin B 12 deficiency. That means if an area of a limb is witnessing symptom, then corresponding area on opposite side will be enduring symptom of neuropathy as well.


Important note:

Peripheral neuropathy is not exclusive to very low B 12 symptoms. It can happen in sustained uncontrollable diabetes. It is even more frequent in people on long term metformin ( antidiabetic ) use. 

b. Subacute combined degeneration of spinal cord ( SCD )

This is a disease of spinal cord. This ensues due to loss of myelin ( demyelination ) following severe vitamin B 12 deficiency. It is called combined degeneration because both muscle movement and sensation is compromised here.

  • This impacts lower extremities relatively more. Muscles become spastic and weak. Patient finds it difficult to walk.
  • Furthermore in SCD, potential to asses position of joints is lost. Besides there is inability to perceive vibration sensation as well.
c. Cognition defect

Cognition is a process of thinking, perceiving, logical reasoning and taking judgement based on own knowledge and experience. Cognitive ability weakens in vitamin B 12 deficiency.

d. Dementia

Dementia is a term that describes incapacity to remember and think properly, so much so that it affects day to day activity. Vitamin B 12 deficiency potentially leads to dementia.

e. Neural tube defect

We have outlined previously in our blog on “5 critical stages of brain growth and development “ that how brain and spinal cord develop from such a tiny structure like “neural tube”. And any defect in neural tube development inflicts permanent defect in brain and spinal cord. 

Folic acid is very essential to prevent neural tube defect. Along with vitamin B 12 level in mother also also plays an independent and crucial role in neural tube development. 


f. Delay in development and regression in developmental milestones

Profound vitamin B 12 deficiency can present as delay in developmental milestones in a baby. It may also cause regression of milestones. That means, suppose a child who was previously able to stand and walk, will progressively lose its ability to walk and then to stand. 

In case this happens many a times physicians evaluate for other causes, yet ignoring B 12 deficiency. A simple serum B 12 level, MMA test ( methylmalonic acid level ), Homocysteine level, detection of macrocytic anaemia can help to rule out vitamin B 12 deficiency. 

If child is treated early then developmental disease can be reversed altogether and outcome is very good. If not and it remains untreated for too long then it is irreparable.

g. Learning difficulty

Kids who have low vitamin B 12 levels are slow to learn. They find it challenging to concentrate on a topic.


h. Vision abnormality

Very seldom vitamin B 12 deficiency can cause vision impairment. This happens due to damage to optic nerve. Optic neuropathy hence produced is reversible and treatable, if patient is treated on time with vitamin B 12. 

But if it proceeds to optic atrophy ( wasting of optic nerve ) then it is irreversible.

i. Psychological disorder

Sometimes vitamin b 12 deficiency can also roll out as psychological disorders like depression, psychosis, mania etc. It is quite surprising indeed. 


j. Movement disorder

Though it is an unusual presentation of vitamin b 12 deficiency, but it should never be ignored. Affected person presents with various type of abnormal movements which many a times mimic a neuro-degeneration diseases. But if it is picked early and treated, then can be reversed dramatically. 

Age wise presentation of vitamin b 12 deficiency

Severe vitamin B 12 deficiency symptoms age wise is as below. 

  • In children less than 6 years, most prevalent is neurological abnormalities 
  • More than 6 years it commonly exhibits hematological abnormalities 

Caution Important note:

Following treatment with vitamin b 12, improvement occurs in following order. Blood counts get better in 2 months, whereas neurological correction takes up to 6 months.


Never ignore vitamin B 12 deficiency, especially when you are vegan or vegetarian or diabetic. Vitamin b 12 deficiency is still an under-diagnosed and under-treated condition due to lack of suspicion. Share this article maximum and hence help to spread awareness about the same.


All the informations provided here are for educational and awareness purpose only. Kindly do not use these as alternative to medical consultation.

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