Dr. C.N. Srinivas
Head of Laboratory Services
SRL Diagnostics, Chennai.

Vitamin B12 is also known as cobalamin. It is a water soluble vitamin like other B-complex group of vitamins. Natural sources of Vitamin B12 include animal sources like fish, meat, and dairy products. Fortified cereals and supplements do have vitamin B12 in them. It is crucial for the proper functioning of neurons, production of red blood cell, and synthesis of DNA, and acts as a cofactor for various metabolic processes.

Common causes of Vitamin B12 deficiency include poor absorption from the stomach or intestines, decreased intake, and increased requirements. Decreased absorption may be due to conditions such as pernicious anemia, surgical removal of the stomach, chronic inflammation of the pancreas, intestinal parasites, certain medications, and some genetic disorders. Decreased intake may occur in those who eat a vegan or vegetarian diet or have malnutrition. Increased requirements occur in HIV/AIDS and in those with rapid red blood cell breakdown.

Vitamin B12 deficiency is widespread in Indian population. A study showed the prevalence of vitamin B12 deficiency in Indian population as 47%. However, other studies have reported a deficiency ranging from 16% to 77%. This large prevalence may possibly be due to a large majority of Indian population being vegetarian by food habits. In pregnancy, deficiency of vitamin B12 has been estimated to have prevalence of 43% to 74%.

Vitamin B12 deficiency has varying sequelae affecting multiple systems. The symptoms may range from mild fatigue, tingling in the hands and feet, palpitation, skin hyperpigmentation, irritability and glossitis to severe conditions like depression, megaloblastic anemia (due to bone marrow suppression), infertility and neurologic impairment. Neurologic symptoms are caused due to progressive demyelination and can manifest as peripheral neuropathy, areflexia, and loss of proprioception and vibratory sense. More severe and chronic deficiency can lead to dementia and episodes of psychosis. Usually the severity of megaloblastic anemia inversely correlates with the degree of neurologic impairment. Babies born to mothers who are vitamin B12 deficiency do not get enough vitamin B12. In young children symptoms include poor growth, poor development, and difficulties with movement.

The clinical manifestation of vitamin B12 deficiency may be masked for up to 10 years. This is because liver has sufficient storage of vitamin B 12 and the depletion process may take years to become clinically evident. Early and reliable diagnosis of deficiency is crucial, owing to the latent nature of the disorder and the resulting possible irreversible neurologic damage.

The recommended laboratory evaluation for patients with suspected vitamin B12 deficiency includes a complete blood count (CBC) with peripheral smear examination and serum vitamin B12 level. There will be anemia with high MCV value on CBC and macrocytes on the peripheral smear. Serum vitamin B12 levels will be low. Although, low serum vitamin B12 may not always be associated with anemia or neurological complications, chronic vitamin B12 depletion (i.e., prolonged low intake or intestinal malabsorption) results in a state of negative vitamin B12 balance. In patients with a normal or low-normal serum vitamin B12 level with suspected clinical features, a serum methylmalonic acid level is an appropriate next step and is a more direct measure of vitamin B12’s physiologic activity. Measurement of holotranscobalamin, the metabolically active form of vitamin B12, is another emerging method of detecting vitamin B12 deficiency.
Even with suspected features of deficiency, serum vitamin B12 levels may be elevated in patients with alcoholism, liver disease, or cancer because of decreased hepatic clearance of transport proteins and resultant higher circulating levels of vitamin B12.

Without early diagnosis and treatment some of the changes may become permanent. There is a significant need for reaching out and making people aware of vitamin B12 deficiency and the importance of testing for vitamin B12 levels.