Vitamin B12 is a water soluble vitamin which plays a key role in the normal functioning of the brain and nervous system, as well as in the formation of red blood cells. No fungi, plants or animals (including humans) can make B12. Only bacteria have the enzymes needed for this process.
Vitamin B12 was discovered due its relationship to pernicious anemia, an autoimmune disease in which parietal cells of the stomach (which release intrinsic factor) are destroyed. These cells are also responsible for making stomach acid. Intrinsic factor is essential for B12 absorption, so for people with pernicious anemia, the only way to get sufficient B12 is from an intramuscular injection.
Most of B12 is absorbed in the terminal ileum -which is part of your bowel, and removal of this in people who have Crohn’s disease, for example, can cause B12 deficiency.
Vitamin B12 is needed to keep the myelin sheaths around nerves in good condition. B12 deficiency can affect nerve cells in many ways, causing changes such as confusion, depression, irritability, poor concentration, as well as physical problems such as tingling and numbness in fingers, difficulty with balance and altered sensation.
Another problem related to low B12 is that blood levels of homocysteine increase, accelerating atherosclerotic plaque growth and contributing to clogged arteries.
Good bacteria in the gut produce B vitamins and vitamin K. When people take antibiotics they kill off good bacteria and contribute to lower levels of vitamin B. When antibiotics were first marketed, they were always given together with B vitamins, and it is not clear when this practice stopped or why. Taking a a good balance of B vitamins is essential - a lot of multivitamins now have quite high levels of folic acid (Vitamin B9), which can mask B12 deficiency, causing permanent neurological damage.
As the only good food sources of B12 are animal products, it is essential for vegans to supplement with B12 or to ensure regular use of fortified products such as cereals. Another group at risk is people over 50 as B12 absorption decreases with age. In animal products, B12 is bound to protein and as people age, they produce less stomach acid making it harder to split the B12 off the protein, and this creates deficiency in many seniors. Other factors that worsen the problem include using laxatives, antacids, antibiotics and alcohol.
The good news is that B12 is only needed in tiny quantities. It is found in sufficient amounts in fortified cereals, fortified non dairy milks, and some brands of nutritional yeast. It is also found in all common multivitamins, - just look on the label for “cyanocobalamin” or vitamin B12.
In order to obtain adequate vitamin B12, take a daily supplement with at least 25 micrograms. Some experts recommend up to 250mcg daily for adults up to 65 and as high as 1000mcg daily for seniors ( any excess will easily be excreted by the body.
There are also high dose tablets which can be taken once or twice a week, but it can be easy to forget when you are not taking them daily!