Martyn Hooper’s latest blog posting talks about a patient who was given 5000 mcg of folic acid a day - despite having a B12 deficiency that couldn’t be treated until after Xmas.
In his post Martyn mentions the Folate Trap - I thought I’d explain what that is.
Folate is a term used by biologists to cover a group of chemicals all with a similar structure. Different folates take part in different biochemical reactions. Normally we are interested in just one (because it also involves B12). That is the conversion of homocysteine to methionine. The attached image shows how this happens.
You can see from the diagram that methylfolate and cob(II)alamin (from B12) work together in the reaction. In the process the methylfolate is converted to tetrahydrofolate, which is then available to go around the cycle again - or to take part in other reactions. Many of these other reactions involve DNA (see diagram).
If there’s not enough B12 in the body then this conversion cannot take place at the normal rate. And this is the only way that methyltetrahydrofolate (AKA methylfolate) can be converted to anything else. Without enough B12 the methylfolate builds up.
Which wouldn’t be too bad, except that all other forms of folate (that get used in other reactions) will, eventually, get converted to methylfolate. And that’s where it will get stuck.
Slowly the majority of folate in the body is methylfolate - which is useless. All the other forms of folate aren’t available, so the reactions that involve them aren’t progressing as they should. The patient starts getting ill.
But the blood test measures all forms of folate. So it sees a lot of folate present and doesn’t know it’s all methylfolate. Nobody is quite sure if these high levels of methylfolate are dangerous. Signs are that it might be.
Which is why folate shouldn’t be given in high doses until a B12 deficiency is ruled out or treated.
I've noticed that HU shrinks images. Here's a link to the full-size, readable, original - frankhollis.com/temp/B12%20...