Er store doser av B12 nyttig eller skadelig?
Siden B12 er et vannløselig vitamin, anses det generelt for trygt, selv ved høye doser.
Det er ikke etablert noe tolerabelt øvre inntaksnivå (UL) for B12 på grunn av det lave giftighetsnivået. UL refererer til den maksimale daglige dosen av et vitamin som er usannsynlig for at det skal forårsake uønskede bivirkninger.
Denne grensen er ikke satt for B12 fordi kroppen din skiller ut gjennom urinen det den ikke bruker.
Men å tilføre for store doser av B12 har vært knyttet til noen negative bivirkninger.
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Is Taking High Doses of B12 Helpful or Harmful?
Since B12 is a water-soluble vitamin, it's generally considered safe, even at high doses.
No Tolerable Upper Intake Level (UL) has been established for B12, due to its low level of toxicity. UL refers to the maximum daily dose of a vitamin unlikely to cause adverse side effects in the general population.
This threshold has not been set for B12 because your body excretes whatever it doesn't use through your urine.
However, supplementing with excessively high levels of B12 has been linked to some negative side effects.
Several studies have shown that megadoses of the vitamin can lead to outbreaks of acne and rosacea, a skin condition that causes redness and pus-filled bumps on the face.
Yet, it should be noted that most of these studies focused on high-dose injections rather than oral supplements (5, 6, 7).
There is also some evidence suggesting that high doses of B12 may lead to negative health outcomes in those with diabetes or kidney disease.
One study found that people with diabetic nephropathy (loss of kidney function due to diabetes) experienced a more rapid decline in kidney function when supplemented with high-dose B vitamins, including 1 mg per day of B12.
What's more, the participants receiving the high-dose B vitamins had a greater risk of heart attack, stroke and death, compared to those receiving a placebo (8).
Another study in pregnant women showed that extremely high B12 levels due to vitamin supplements increased the risk of Autism Spectrum Disorder in their offspring (9).
Though there is evidence that supplementing with B12 may cause negative health outcomes, studies have demonstrated that daily oral supplements of up to 2 mg (2,000 mcg) are safe and effective in treating B12 deficiency (10).
For reference, the recommended daily intake (RDI) of vitamin B12 is 2.4 mcg for both men and women, though pregnant and breastfeeding women have a higher need (11).
SUMMARYAlthough there is some evidence that very high doses of B12 may cause adverse health effects in certain populations, megadoses of this vitamin are commonly used to safely and effectively treat B12 deficiency.