http://www.lewrockwell.com/fontova/fontova36.html

Exerpted from:   "Vegans" crusade not only against eating meat itself, but
against the consumption of dairy products. So while vegetarians suffer from
a Vitamin B-12 deficiency, these "vegans" are totally starved of one of the
most essential elements to a properly functioning central nervous system.
According to the Andrews University Nutrition Council (themselves
vegetarians who take it in pill form), a vitamin B-12 deficiency leads to a
range of serious psychiatric disorders. These include, "disorientation,
depression, mood disturbances, irritability, memory loss, and
dementia....Vitamin B12 deficiency is fairly common in the elderly and is
associated with dementia and other neurological disorders seen in the
geriatric population.... Vitamin B-12 is essential for the development of
red blood cells and it plays an important role in the normal function of the
nervous system."