Studies on the Breakdown of B12 Methylcobalamin by Light Keywords: photodecomposition | photodissociation | photolysis | decomposition | degradation | disintegration I just came across a few studies on the breakdown of B12 methylcobalamin by light: The study: "Stability of high-dose methylcobalamin injection" found that in ampoules of injectable methylcobalamin which were wrapped in aluminum foil to protect them from light, around 92% of the methylcobalamin was still present 6 months later. So in the absence of light, methylcobalamin is reasonably stable. However, the above study found that an astounding 50% of the methylcobalamin in the ampoules disintegrated after only 4 hours exposure to bright light of 1000 lux (= about the light level you get at 1 meter from an ordinary 60 Watt light bulb). Ampoules, of course, contain methylcobalamin in aqueous solution, and whether this presence of water increases methylcobalamin's tendency to breakdown in light, I am not sure. I think Freddd did mention something about water increasing the instability of methylcobalamin, but I cannot find any studies on this. In any case, even if you find a good quality jar of B12 methylcobalamin supplement that is potent, it would seem prudent to wrap that jar in aluminum foil or similar, to completely protect it from light, as both glass and plastic vitamin containers tend to transit some light through them. And/or you might keep your jar of B12 methylcobalamin in a dark draw, away from light. By contrast, it seems B12 methylcobalamin is reasonably stable to heat: this article mentions that: "In neutral media and in the absence of light, the carbon—cobalt bond in methylcobalamin is very stable to thermal breakdown, and the molecule can even stand heating to 100°C for 20 minutes." The article also states that "Because methylcobalamin is highly labile upon exposure to light the whole manufacturing process and the analytical controls require an effective protection from light."