Hydroxy B12 (60 Sublinguals)

You might think that this is the kind of obscure little factoid that gets put into biology textbooks or turns up on Final Jeopardy, but which has no real-world importance. "My diet and supplement program includes plenty of B12," you might think, "so my body will make all the B12 coenzymes I could ever want or need."

Like the old song says, It ain't necessarily so. While a good diet and supplement program usually guarantees the body a generous supply of adenosylcobalamin (unless you have a deadly genetic defect), the same cannot be said of Methylcobalamin. While adenosylcobalamin is readily stored up in the liver (and, to a lesser extent, the kidneys and other tissues), methylcobalamin's job requires that it be free to circulate in body fluids like cytosol (the liquid medium of the cell), plasma, and the fluid that bathes the brain and spinal cord (cerebrospinal fluid). Because of this, Methylcobalamin doesn't hang around in the body for very long.

Thus, while a person getting enough of the basic vitamin (cobalamin) will always have plenty of adenosylcobalamin, the nervous system has no special store of protective Methylcobalamin on which to rely. In fact, the body's Methylcobalamin "fuel tanks" can easily be brought below optimal levels, and the supply is quickly depleted if it is not constantly replenished.

When you take a regular B12 (cyanocobalamin) supplement, the body must first convert its B12 into Hydroxycobalamin order to form the B12 coenzymes. This involves the removal and detoxification of the cyanide molecule, followed by biochemical reduction to a less oxidized (+1 valence) state, and then the enzymatic conversion of the reduced cobalamin into one of two metabolically active coenzyme forms. By taking a preformed Hydroxycobalamin supplement, you can skip over this first biochemical stumbling block, allowing for unhampered formation of adenosylcobalamin and Methylcobalamin.

Methylcobalamin or Hydroxycobalamin?
Because the body can interconvert the two B12 coenzymes, and because the body stores adenosylcobalamin but not Methylcobalamin, an adequate supply of Methylcobalamin usually ensures that you'll have plenty of adenosylcobalamin, too - but not vice-versa. Because of this fact, and because of the powerful neuroprotective effects of Methylcobalamin, a fully-formed Methylcobalamin supplement is the best choice for most people.

One key exception is persons with known or suspected cyanide toxicity, where Hydroxycobalamin has an unique role to play. Hydroxycobalamin helps the body to rid itself  of cyanide, both by reacting with the toxin to form cyanocobalamin (which can then be excreted) and by enhancing the detoxification of cyanide through its conversion into the less toxic thiocyanate. In isolated human cells, Hydroxycobalamin penetrates cyanide-laden cells and detoxifies the toxin directly. Hydroxycobalamin has a long history of intravenous use for acute, life-threatening cyanide toxicity (such as during industrial disasters) and is approved for this use in many European countries. At lower doses, oral Hydroxycobalamin increases the urinary excretion of thiocyanate in laboratory animals fed cyanide-containing diets. Sublingual Hydroxycobalamin is an ideal choice for a B12 supplement in persons concerned with chronic, low-level cyanide toxicity.