Maria,
http://www.yourhealthbase.com/vitamin_B12.html
"oral supplementation with vitamin B12 is safe, efficient and inexpensive. Most multi-vitamin pills contain 100-200 microgram of the cyanocobalamin form of B-12. This must be converted to methylcobalamin or adenosylcobalamin before it can be used by the body. The actual absorption of B12 is also a problem with supplements. Swallowing 500 micrograms of cyanocobalamin can result in absorption of as little as 1.8 microgram so most multivitamins do not provide an adequate daily intake. The best approach is to dissolve a sublingual tablet of methylcobalamin (1000 micrograms) under the tongue every day. That will be sufficient to maintain adequate body stores. However, if a deficiency is actually present then 2000 microgram/day for one month is recommended followed by 1000 microgram/day. Some physicians still maintain that monthly injections of vitamin B12 is required to maintain adequate levels in the elderly and in patients with a diagnosed deficiency.
There is however, no scientific evidence supporting the notion that injections are more effective than sublingual supplementation."
Vitamin B-12 - Is oral supplementation effective?
CAMBRIDGE, UNITED KINGDOM. It is common medical dogma that patients suffering from pernicious anaemia are unable to absorb sufficient vitamin B-12 from their diet and therefore require intramuscular injections of the vitamin on a regular basis. Recent research is questioning this assumption. In a commentary in The Lancet Dr. M. Elia of the Dunn Clinical Nutrition Centre persuasively outlines the reasons why oral supplementation is at least as effective as intramuscular injections. Dr. Elia points out that vitamin B-12 is absorbed from the intestine via two different routes. One involves intrinsic factor and is estimated to lead to absorption of about 60 per cent of the amount of vitamin B-12 ingested in the diet. The other does not need intrinsic factor (which is absent in pernicious anaemia patients) and only leads to absorption of about 1 per cent of the ingested amount. The body needs about 1-2.5 micrograms/day so oral supplementation with 100-200 micrograms/day should be adequate. However, Dr. Elia suggests a daily intake of 1000 micrograms/day is needed to ensure successful long-term results in patients with pernicious anaemia. A recent study showed that oral supplementation with 2000 micrograms/day was three times as effective as intramuscular injections in increasing vitamin B-12 levels in pernicious anaemia patients. Dr. Elia also questions whether the current RDA (Recommended Dietary Allowance) of 1-2.5 micrograms/day is adequate for older people. He points out that mild vitamin B-12 deficiency, which can lead to abnormalities in cognitive function and increased risk of cardiovascular disease, affects 12-15 per cent of all elderly people in the United States where the average daily vitamin B-12 intake is about six micrograms - well above the RDA.
Elia, M. Oral or parenteral therapy for B12 deficiency. The Lancet, Vol. 352, November 28, 1998, pp. 1721-22 (commentary)
Oral vitamin B12 and pernicious anaemia
MINNEAPOLIS, MINNESOTA. Pernicious anaemia can be treated with intramuscular injections of cobalamin (vitamin B12). These injections can be painful and expensive, but are still widely used despite the fact that research done 30 years ago clearly established that oral doses of one mg/day of vitamin B12 are effective in treating pernicious anaemia and other cobalamin deficiency disorders. The problem, according to Dr. Frank Lederle, MD of the Minneapolis Veterans Affairs Medical Center, is that physicians are unaware that oral cobalamin works. Dr. Lederle performed a survey among Minneapolis internists in 1989 and again in 1996. In 1989 none of the 245 respondents used oral cobalamin in the treatment of pernicious anaemia. In 1991 a review of the use of oral cobalamin was published in the Journal of the American Medical Association. A subsequent survey in 1996 showed that 19 per cent of the 223 internists responding were now using oral cobalamin. However, even in 1996, 71 per cent of the internists still held the incorrect view that sufficient quantities of cobalamin cannot be absorbed from oral supplements (91 per cent of the internists held this view in 1989). Dr. Lederle concludes that the majority of Minneapolis interns are still unaware of the oral treatment option.
Lederle, Frank A. Oral cobalamin for pernicious anemia: back from the verge of extinction. Journal of the American Geriatrics Society, Vol. 46, September 1998, pp. 1125-27
Oral administration of vitamin B-12 is effective
BRUSSELS, BELGIUM. Older people are often found to have a vitamin B-12 deficiency even though they do not suffer from pernicious anaemia. The body's ability to absorb vitamin B-12 from food decreases markedly with age probably because of a lack of stomach acid. The conventional way of correcting a vitamin B-12 deficiency has been through intramuscular injection of the vitamin. Now researchers at the Universities of Brussels and Antwerp report that oral administration of free vitamin B- 12 is effective in normalizing low vitamin B-12 levels. Their experiment involved 94 patients without pernicious anaemia with a mean age of 84 years who through repeated tests had been found to have an average vitamin B-12 level (in serum) of 146.5 ng/L. The patients were treated for one month with 100 micrograms/day of vitamin B-12 taken as an oral solution of the vitamin in water (10 ml of a solution containing 1 mg vitamin B-12 in 100 ml water). After 10 days 69 per cent of the patients had normal vitamin B-12 levels (271.5 ng/L average) and after 30 days 88 per cent had achieved normal levels (371.2 ng/L average). The researchers conclude that older patients with a vitamin B-12 deficiency unrelated to pernicious anaemia can be successfully treated with orally administered vitamin B-12.
Verhaeverbeke, I., et al. Normalization of low vitamin B-12 serum levels in older people by oral treatment. Journal of the American Geriatrics Society, Vol. 45, No. 1, January 1997, p. 124 (letter to the editor)