Everyone knows that vitamins are essential for the healthy, efficient functioning of both the body and the mind. In the body, vitamins function as coenzymes and cofactors in the millions of chemical reactions that occur every second. Some people even take large or “megadose” amounts of vitamins in the hope of promoting health and longevity. This is self- defeating, as excess water-soluble vitamins are excreted in the urine. In contrast, fat-soluble vitamins can remain in the body and reach toxic levels.
The body does not make vitamins. Most of our vitamins are obtained from a balanced and nutritious diet. Deficiencies can occur in strict vegans, those on highly restricted or unfortified liquid diets, those who have had radiation or surgery, and in seniors.
The fat-soluble vitamins (A, D, E, and K) are stored in the body for long periods. In contrast, the water-soluble vitamins (the B-complex group and vitamin C) are not stored. They must be supplied regularly through the diet.
Within this group, vitamin B12 is an exception. Unlike other B vitamins, it is found mainly in meat, fish, and dairy products rather than in leafy vegetables or fruits. Moreover, while most B vitamins are destroyed by heat and cooking, vitamin B12 remains relatively stable. The body can store about 1 to 5 milligrams of vitamin B12, so symptoms of deficiency may take several years to appear.
The absorption of vitamin B12 is more complex than that of other water-soluble vitamins. The process begins in the mouth, where vitamin B12 binds to a protein called haptocorrin in the saliva, and then binds to another protein known as intrinsic factor, which is secreted by the parietal cells of the stomach. This new complex is then absorbed in the ileum, the final part of the small intestine. When vitamin B12 is added to fortified foods or taken as a supplement, it can be absorbed more directly but still needs to bind to intrinsic factor.
Vitamin B12 deficiency can occur because of an inadequate diet, particularly one that lacks animal products. Sometimes, xerostomia (dry mouth) can reduce saliva and interfere with absorption. The gastric glands that produce intrinsic factor can become damaged and replaced by fibrous tissue. This can occur in thyroid disorders or autoimmune diseases. Chronic Helicobacter pylori infection, as well as regular use of tobacco or alcohol, can also reduce absorption. Intestinal diseases or surgical procedures such as partial removal, banding, or bypass of the stomach or small intestine, or weight-loss surgery, can further contribute to falling vitamin B12 levels.
Metformin is one of the most used drugs for the control of diabetes. Proton pump inhibitors such as omeprazole and pantoprazole, and antacids like cimetidine, ranitidine, and famotidine are widely prescribed. These medicines, along with certain anti-epileptic drugs such as phenytoin and phenobarbital, can also lower vitamin B12 levels.
Vitamin B12 requirements are about 0.4 mcg per day in infants and 2.4 mcg per day in adults. Pregnant and lactating women need slightly more, around 2.8 mcg per day. Foods rich in vitamin B12 include liver, beef, fish, eggs (especially the yolk), and dairy products such as curd, paneer, and cheese.
All cells contain DNA, and vitamin B12 is a key nutrient required to produce DNA in all dividing cells. It is essential in the formation of red blood cells. A deficiency can lead to a type of anaemia in which the red blood cells are larger than usual and less efficient (megaloblastic anaemia). The nerves are also affected, as B12 is needed to maintain the protective myelin sheath that insulates them and is crucial for the synthesis of neurotransmitters that allow nerves to communicate. Without enough B12, nerves can become damaged, leading to symptoms such as numbness, tingling and weakness. Severe deficiency can result in more serious neurological problems, including spinal cord damage, loss of balance, cognitive impairment, and forgetfulness.
If symptoms suggest a possible vitamin B12 deficiency, a blood test should be done. A level of around 300 pg/ml is considered normal. If a deficiency is detected, the underlying cause must be identified and addressed along with corrective treatment. Medicines should not be stopped without a doctor’s advice, even if they contribute to low B12 levels. When the cause cannot be corrected, replacement therapy should be started. In mild cases where absorption is intact, vitamin B12 capsules or tablets containing 250–1000 mcg can be taken daily. They may be prescribed alone or in combination with folic acid and other B-complex vitamins. If the deficiency is severe or the absorption is impaired, vitamin B12 injections can be given daily for one week, followed by weekly doses for six weeks. Monthly maintenance injections may then be required for the rest of one’s life. Blood levels should be rechecked after three months of treatment.
As we age, vitamin deficiencies can develop gradually and often go unnoticed. These deficiencies may aggravate symptoms such as fatigue and age-related memory loss. The good news is that they are often reversible with timely correction.
The writer is a paediatrician and author of Staying Healthy in Modern India.