- Nutrition of the Human/ Ernährung des Menschen by Ibrahim Elmadfa and Claus Leitzmann, p.476Newer findings show that 10-30% of the vitamin B12 in vitamin supplements are metabolized to inactive derivatives/derivates(?) and to subtances with antivitamin character by/ because of the redox potential of vitamin C and B1, copper, iron and other antioxidants
I have a sublingual b12 supplement which contains vitamin C, so I ordered another one without it.
- Nutrition of the Human/ Ernährung des Menschen by Ibrahim Elmadfa and Claus Leitzmann, p.475Around a third of vitamin B12 in serum belong to not vitamin active corrinderivatives. Due to this, microbiological tests often don't show a deficiency, since normal vitamin B12 levels (including not active corrinderivatives) are found.
I am a bit shocked by these two quotes, I found them in a book and cannot find any similar information confirming this online.