There are three forms which are important those are methylcobalamin (MeCbl), adenosylcobalamin (AdCbl), and hydroxycobalamin (OHCbl). They can help boost immune system, digestive system and overall health.
It cannot be called C12 even if the central molecule is cobalmin. It is called B12 only.
There is no sure shot way to decrease vitamin B12 levels, however, research hints that drinking alcohol moderately helps in decreasing vitamin B12 levels to a certain extent.
Yes, vegetarians and vegans are at a risk of vitamin B12 deficiency. Additionally, it has been reported that 1.5 to 15% people globally have vitamin B12 deficiency.
Vitamin B 12 plays a major role in digestion by providing the gut with enough supply of red blood cells. Lack of B12 has been associated with poor gut health affecting digestion and often inducing loose motions. Hence, taking adequate amount of B 12 is recommended to maintain proper digestive function.