Updated: Oct 4
The Conclusion of this study 2013 study on 100 vegetarians and 100 meat eaters is that vegetarians are more likely to have a B12 deficiency and prone to developing neuropsychiatric and neurological issues. In the vegetarian group, the frequency of depression was 31% compared with 12% in the omnivore and the B12 levels were significantly lower.
The best sources of B12 come from meat and fish, however eggs and yoghurt do also contain reasonable amounts. B12 plays a critical role in a process called methylation which is needed to create and breakdown neurotransmitters (brain chemicals) and is a crucial nutrient for many aspects of neurological health. Symptoms of low B12 include irritability, apathy, depression, memory loss, dementia, tremor and chronic fatigue.
Vegetarians need to ensure that they are getting enough B12 from their diet in the form of eggs and dairy (if they can tolerate these foods). For vegans it is even more difficult to get this nutrient so supplementation is very useful. Certain types of B12 are more absorbable than others and usually should be taken in conjunction with other B vitamins.