Symptoms are too many to list and can vary tremendously, even within an immediate family
Most people can continue in good health for a couple of years without absorbing any B12 at all. This is possible because the amount necessary for use over a three to five year period is stored in the normal body. But after many years of absorbing too little, or after a couple of years absorbing none, subtle symptoms begin to occur. Those symptoms are often dismissed with rationalizations such as: must have slept wrong; must be getting old; must not be exercizing enough; sure am clumsy today; etc.
Symptoms that are slight and progressing very slowly are often not even noticed. For instance: lessened sensation might go unnoticed unless revealed by a doctor's examination; changes in vision that may not be recognized until an eye exam; skin quality and color changes so subtle they aren't noticed; etc.
Many problems develop so slowly that when they become noticable they are described as "sudden" or "new." And problems are often assumed to be unrelated. Thus, energy and time are wasted and something systemic, such as B12 deficiency, is often not considered. When a variety of symptoms confuse medical people, that is one more reason to suspect advanced B12 deficiency.
Even members of the same family are sometimes affected very differently. One might show signs of anemia and develop more energy and heart symptoms than others who do not become anemic and have primarily neurological symptoms. Rarely a person develops severe psychological problems up to and including psychosis before anything else is noticed. And many are misdiagnosed with Alzheimer's or die of heartfailure due to B12 deficiency, without having been diagnosed and treated.
This is excerpted from a mainstream medical textbook, one of the better sources of information:
Goldman: Cecil Textbook of Medicine, 22nd ed., W. B. Saunders Company,
Chapter 175, page 1054
None of these abnormalities are specific for cobalamin deficiency [B12 deficiency], and any of them may be present alone or in any combination and may vary greatly from patient to patient. None of the abnormalities are always seen in cobalamin deficiency, and the absence of any one or a combination of them does not exclude cobalamin deficiency. The neuropsychiatric abnormalities may occur early or late in the course of cobalamin deficiency and with or without any of the hematologic or other abnormalities . . . How the deficiency of a single substance, such as cobalamin, can produce a clinical picture with such wide variations in severity and dissociation of various hematologic [blood] and neuropsychiatric abnormalities is unknown.
[bolding and brackets added by rose]
The same medical textbook estimates that 10% of the population develops B12 deficiency (most often because of acquired malabsorption) by the time they are middle aged or elderly. Imagine the number of people languishing in rest homes and wishing to die for lack of a safe and inexpensive vitamin.
It is important to remember that the sooner treated the better. There is no guarantee that damage will be repaired, although at least some usually is over time. It is surpising how many medical people expect symptoms to disappear as soon as deficiency is eliminated; that is about as reasonable as expecting a knife wound to disappear as soon as the knife is removed. Treatment and what to expect will be addressed on another page.
More to come...