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B12 Deficiency? Here's What Happens Clinically.

Vitamin B12, also known as cobalamin, is one of many water soluble vitamins found in many food sources such as fish, meat, liver, eggs and milk.  Humans are not capable of synthesizing vitamin B12 so we must get it from these dietary sources to prevent b12 deficiency.  Deficiency of vitamin B12 results in many functional and physiological deteriorations in the nervous system, the mood and psyche, the blood and hematological systems, metabolism, and gastrointestinal tract.  It can have an affect on cell division and even lead to reduced blood cells, anemia, shortness of breath, and fatigue.  B12 is also needed for proper fat and amino acid metabolism.

Here we will explore the progressive loss of these physiological functions and how they typically manifest.

 This guy has B12 Deficiency

Clinical Manifestations of B12 Deficiency 

When treating someone for B12 deficiency it is helpful to understand how low their body is.  Increasing the serum B12 levels to an adequate amount will not resolve all the symptoms of b12 deficiency immediately. The symptoms will resolve but it will take time. The amount of time depends on how long the body has been deficient.  So to help understand how long we need to treat someone for b12 deficiency, we should look at that manifestations of b12 deficiency and the symptoms that emerge as you are in a deficient state longer. 


Mood and Psych

Psychiatric manifestation are often the first to manifest and usually precede overt manifestations in the blood (see below).  These include mood disorders such as depression and mania, personality changes, chronic fatigue syndrome, psychosis and cognitive impairment.1  Among these we typically see fatigue and low energy as one of the first presenting symptoms of b12 deficiency.



Neurological/neuropsychiatric manifestation occur due to defective myelin (nerve sheath) synthesis and nerve (axonal) degeneration. These manifestations also precede the hematological problems and include myelopathy, neuropathy, neuropsychiatric abnormalities and, less often, optic nerve atrophy.1, 2

The spinal cord may also be affected, a condition known as sub-acute combined degeneration of the cord. This is characterized by abnormal sensations, limb weakness, and gait disturbance. Others are bladder and erectile dysfunction.


Optics and Eyes

Involvement of the eyes may be seen in some patients with vitamin B12 deficiency. This is known as optic neuropathy. It manifests as painless and progressive visual loss usually affecting both eyes.


Gastrointestinal and Digestion

One symptoms that often baffles people as to the cause is glossitis or painful swollen tongue.  Along with glossitis, is pain with eating and swallowing in general.  This is directly related to b12 deficiency and many times will resolve with proper treatment.1

When b12 deficiency is present longer, it can start to affect the small intestine leading to deterioration of the surface area of the intestines  The surface area known as the villi and microvilli are the most important aspect of the small intestine.  Once this takes place it becomes even more difficult to absorb b12 and often leads to bowel changes like diarrhea or constipation. The gastrointestinal manifestations typically occur along with or in conjunction with the hematological (anemia) manifestations noted below. 


Blood and hematological

At some point vitamin b12 deficiency will cause decreased production of red blood cells.  These hematological findings often show up after the above listed symptoms have been going on for some time.  Once anemia is present additional symptoms may manifest. These symptoms include: increased fatigue, difficulty in breathing or shortness of breath with mild exertion, dizziness.1  

Specific lab tests will show decreased red blood cells and an increase in Mean Corpuscular Volume (abnormally large red blood cells), reduction in red cell hemoglobin (pale red cells) and hypersegmented neutrophils.1


Vitamin B12 Deficiency Resolution

As with any deficiency in vitamins and nutrients, we should always be asking why there is a deficiency to being with. What caused the deficient state? B12 deficiency is no different and this helps us understand what is needed to correct the deficiency.  For instance, if your deficient state is occurring from a genetic need for more, there is not much more you can do other than increase the amount you are getting on a daily or weekly basis. However, if your deficiency is coming from poor absorption due to a digestive disorder, you can try to resolve or fix this and therefor improve your levels over the long term. 

The specific plan for resolving your b12 deficiency will be highly dependant on your specific situation creating the deficeincy.  However, and possibly more important, what is your current manifestations of b12 deficiency?

 If you have anemia from a b12 deficiency this is going to take longer and require more persistence than if you simply have mild fatigue from your b12 deficiency. 

So what about your b12 levels and deficiency symptoms? Let us know in the comments below. 

If you want help with creating a customized plan to resolve your b12 deficiency, click on the link below for a consult. 

Schedule Your   Free Consultation!



1. Briani C, Dalla Torre C, Citton V, et al. Cobalamin Deficiency: Clinical Picture and Radiological Findings. Nutrients. 2013;5(11):4521-4539. doi:10.3390/nu5114521.

2. Ralapanawa DMPUK, Jayawickreme KP, Ekanayake EMM, Jayalath WATA. B12 deficiency with neurological manifestations in the absence of anaemia. BMC Research Notes. 2015;8:458. doi:10.1186/s13104-015-1437-9.

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