There is an excellent article on
The National Academies Press titled "Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline" published in 1998. It can be downloaded for free.
The article said...
Adverse Effects
No adverse effects have been associated with excess B12 intake
from food or supplements in healthy individuals. There is very weak
evidence from animal studies suggesting that B12 intake enhances
the carcinogenesis of certain chemicals (Day et al., 1950; Georgadze,
1960; Kalnev et al., 1977; Ostryanina, 1971). These findings are
contradicted by evidence that increased B12 intake inhibits tumor
induction in the human liver, colon, and esophagus (Rogers, 1975).
Some studies suggest a possible association between high-dose,
parenterally administered B12 (0.5 to 5 mg) and acne formation
(Berlin et al., 1969; Dugois et al., 1969; Dupre et al., 1979; Puissant
et al., 1967; Sherertz, 1991). However, the acne lesions were primarily
associated with hydroxocobalamin rather than cyanocobalamin,
the form used in the United States and Canada. Furthermore,
iodine particles in commercial B12 preparations may have been
responsible for the acne. In conclusion, the evidence from these
data was considered not sufficient for deriving a Tolerable Upper
Intake Level (UL).
Studies involving periodic parenteral administration of B12 (1 to 5
mg) to patients with pernicious anemia provide supportive evidence
for the lack of adverse effects at high doses (Boddy and Adams,
1968; Mangiarotti et al., 1986; Martin et al., 1992). Periodic doses of
1 mg are used in standard clinical practice to treat patients with
pernicious anemia. As indicated earlier, when high doses are given
orally (see “Absorption”) only a small percentage of B12 can be
absorbed from the gastrointestinal tract, which may explain the
apparent low toxicity.
Other articles have similar statements on B12 toxicity.
Examples:
Somebody said...
No Upper Limit
There is no known toxicity for vitamin B-12. The body absorbs only a small amount of vitamin B-12, which is why there is no toxicity. Because there are no side effects from large doses of vitamin B-12, no tolerable upper intake was ever established.
From:
www.livestrong.com/article/451351-vitamin-b12-toxicity-level/--- ---
Somebody said...
Toxicity
No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people. Doses as high as 2 mg (2,000 μg) daily by mouth or 1 mg monthly by intramuscular (IM) injection have been used to treat pernicious anemia without significant side effects (84). When high doses of vitamin B12 are given orally, only a small percentage can be absorbed, which may explain the low toxicity (4). Because of the low toxicity of vitamin B12, no tolerable upper intake level (UL) has been set by the US Food and Nutrition Board (17).
From:
lpi.oregonstate.edu/mic/vitamins/vitamin-B12--- ---
Somebody said...
Vitamin B12 is a water-soluble vitamin that is bound to protein in ingested food. Tissue storage capacity of water-soluble vitamins is limited. Water-soluble vitamins are excreted in urine daily. This prevents overdosing. When high doses of vitamin B12 are taken orally, only a small percentage can be absorbed, which may explain the low toxicity.
No Sufficient Evidence of Vitamin B12 Toxicity
No toxic or adverse effects associated with a large intake or overdose of vitamin B12 from food sources or supplements in healthy people have been documented. Approximately 56 percent of a 1mcg oral dose of vitamin B12 is actually absorbed. Absorption actually decreases when the intake amount of the vitamin is increased. There was no sufficient evidence for the Food and Nutrition Board to set a tolerance upper intake level for vitamin B12.
Side Effects of Oral and Injectable Vitamin B12 Supplements
No side effects are generally associated with recommended or increased doses of oral vitamin B12 supplements. Rare allergic reactions to vitamin B12 injections have been reported. It's unclear if the allergic response is to the vitamin or the preservatives and other substances in the solution.
Contraindications for Taking Vitamin B12
Vitamin B12 is contraindicated for patients with early Leber's disease, which is a hereditary optic nerve atrophy. Vitamin B12 can cause severe and sudden optic atrophy, which is a degeneration of the optic nerve.
From:
www.livestrong.com/article/153409-what-are-the-most-toxic-vitamins/So I guess it's safe to take vit B12 in the long term; regardless of my current B12 levels.
If someone has any information/thought to add, please do.
Additional links:
regevelya.com/vitamin-b12-overdose/www.b12-vitamin.com/overdose/Post Edited (xy123) : 7/19/2017 2:17:31 PM (GMT-6)