Answer: they can all mimic the signs and symptoms of vitamin B12 deficiency.
B12 deficiency: an invisible epidemic
B12 deficiency isn’t a bizarre, mysterious disease. It’s written about in every medical textbook and its causes and effects are well-established in the scientific literature.
However, B12 deficiency is far more common than most health care practitioners and the general public realize. Data from the Tufts University Framingham Offspring Study suggest that 40 percent of people between the ages of 26 and 83 have plasma B12 levels in the low normal range – a range at which many experience neurological symptoms. 9 percent had outright deficiency, and 16 percent exhibited “near deficiency”. Most surprising to the researchers was the fact that low B12 levels were as common in younger people as they were in the elderly.
That said, B12 deficiency has been estimated to affect about 40% of people over 60 years of age. It’s entirely possible that at least some of the symptoms we attribute to “normal” aging – such as memory loss, cognitive decline, decreased mobility, etc. – are at least in part caused by B12 deficiency.
More on this article @ chriskresser.com Source: Chris Kresser – Let’s Take Back Your Health website