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Vitamin B12

Vitamin B12 is naturally found in animal food sources. If Vitamin B12 deficiency persists without treatment, you will experience conditions like anemia with abnormally large red blood cells...


Vitamin B12 is a water-soluble vitamin crucial in forming healthy red blood cells, maintaining cell metabolism and the functioning of the brain and nerve cells as well as synthesis of genetic materials like DNA. Methylcobalamin is the metabolically active form of vitamin B12. However, two other forms, Hydroxycobalamin and Cyanocobalamin, the most common type used in supplements, must be processed by the body into the biologically active forms.

Vitamin B12 is naturally found in animal food sources such as meat, fish, poultry and dairy products. It is sometimes fortified in other foods such as cereals or taken as a dietary supplement. If you are severely deficient in the vitamin, vitamin B12 nasal sprays or injections are possible alternative treatments.

Vitamin B12 is not found in plants so people who do not regularly consume animal-based foods like vegans or vegetarians are at risk of having vitamin B12 deficiency. Older people or those with intestinal mal-absorption may also face vitamin B12 deficiency. Because the body stores about 1,000 to 2,000 times as much as the typically daily intake of the vitamin, it can take several years to develop clinical symptoms of vitamin B12 deficiency.

If Vitamin B12 deficiency persists without treatment, you will experience conditions like anemia with abnormally large red blood cells, low counts of white blood cells, platelets, inflammation of the tongue, fatigue, palpitation, muscle weakness, digestive problem, mood disorder, dementia, and nerve dysfunction causing numbness and tingling in the hands and feet. Adults should consume 2.4 micrograms of vitamin B12 daily.

Vitamin B12 has been studied to understand its effects on:

  • Cardiovascular disease
    It was believed that taking vitamin B12, along with folic acid and sometimes pyridoxine (vitamin B6), can lower blood levels of homocysteine, decreasing the risk of stroke and heart disease.
  • Dementia
    Lacking vitamin B12 can lead to dementia and cognitive disorders. But there is no confirmed evidence that the conditions can be avoided or cured by taking vitamin B12 supplements.
  • Sports performance
    Taking vitamin B12 as an oral supplement does not energize or improve your sports performance except in case of vitamin B12 deficiency.

A varied and well-balanced consumption of food allows you to obtain adequate vitamin B12 is preferred. Nevertheless, vitamin B12 supplements are beneficial to the elderly or people with gastrointestinal mal-absorption problem or people who do not eat animal products regularly. Vegetarian or vegan women, especially those who are pregnant or breastfeeding, are advised to take vitamin B12 supplements.

Safety and side effects
A proper daily dosage of vitamin B12 supplement is very safe. It is still harmless if you take a vitamin B12 supplement at a dose higher than the recommended daily allowance which is 2.4 micrograms for adults. Your body usually eliminates the excess vitamin through excretion in the urine by the kidney.

Certain medications may decrease your vitamin B12 absorption capacity, these include:

  • Aminosalicylic acid
  • Colchicine for gout
  • Metformin for diabetes
  • Acid-reducing medicines such as proton pump inhibitors, omeprazole, lansoprazole, etc.
  • Vitamin C supplements
Vitamin C should be taken a couple of hours after taking a vitamin B-12 supplement to prevent undesirable interactions. Taking these 2 vitamins at the same time can decrease vitamin B-12 absorption.

Article by
Dr Prapaporn Phimphilai
Internal Medicine
Doctor profile

Published: 14 Mar 2022