Vitamin B12

Vitamin B12 is the one vitamin that you should consider adding to a totally plant based diet. Even on the usual Australian diet many older persons will need a supplement due to reduced intestinal absorption of vitamin B12. Your doctor can order a vitamin B12 level with your next blood test. More complex tests for active vitamin B12 and vitamin B12 function are available but are not often necessary.

The reason why a modern plant based diet may not provide adequate amounts of this vitamin needs further explanation. It’s not because we are designed to eat a lot of meat. Vitamin B12 is a complex organic molecule with a cobalt atom at its core and it is only synthesized by bacteria. It’s not a part of plant metabolism and the amount present in plants is generally not adequate. All animals require vitamin B12 either from the diet or from gut bacteria. And as it is an essential part of animal metabolism, most animal products contain vitamin B12.  We are well adapted to a low intake of this vitamin – human requirements are only about 3 micrograms per day and the liver can store up to 2 years supply. Not all vegans become B12 deficient as the vitamin can be synthesized by some of our own gut and mouth bacteria but you should not rely on this. Natural sources of vitamin B12 include bacteria growing on unrefrigerated food as well as water and food contaminated with dirt and faeces. Vitamin B12 supplements may be a more palatable option.

Some countries have vitamin B12 added to processed “vegan” food products but this is not generally the case in Australia. And the majority of foods included on a whole foods plant based diet are in an unprocessed state when purchased.

Vitamin B12 is not easily absorbed from the gut. There is a complex active absorption system that can only cope with a few micrograms per meal. Therefore small amounts more often may be better than infrequent large doses. On the other hand it is known that 1-2% of a large dose is absorbed passively so that higher dose B12 supplements may even be adequate regardless of the state of one’s active absorption system.

Vitamin B12 supplements range from 100mcg up to 1000mcg per tablet. High doses are considered safe. You might take one every day, every few days or if you wish to economize on tablets, a quarter once or twice a day.


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Page last updated 5 June 2017