The Methylmalonic Acid Test, also called an MMA Test is a more accurate test of B12 deficiency. Methylmalonic Acid, also called Methylmalonate, is a waste product that builds up in the blood and is excreted in the urine when Vitamin B12 is not available to transform into the energy metabolite Succinic Acid. Because it begins to build up within ten days after a Vitamin B12 deficiency begins, it is not only the most accurate marker, but it is the earliest detectable marker of Vitamin B12 deficiency. And because Methylmalonic Acid is found in both blood and urine in amounts relative to the degree of deficiency, both urine and blood tests are good tests for Vitamin B12 deficiency.
B12 is released from proteins by stomach acid and digestion. Older people and those with low stomach acid or faulty digestion may develop B12 deficiencies (along with other nutrient deficiencies) because of this. Enzymes, particularly the proteases, digest the proteins and may make more B12 available (along with other nutrients). If you take anything that inhibits digestion or stomach acid, then you are inhibiting B12 release and absorption: like calcium carbonate with meals, Tums, Rolaids, and certain medications which affect stomach acid. Further in regards to ME/CFS, inflammation turns out it lowers our zinc levels which is needed for stomach acid production along with B1 and B6. Prolonged inflammation can deplete your B12 over time. If you have an injured gut by any means, you sharply reduce your ability to absorb B12. If you go grain and dairy free in addition to this, you are very likely to be B12 deficient. There is quite high B12 in milk, most better tolerate A2 milk vs normal A1 milk. vitamin B12 can not be manufactured by any plants, and therefore is only found in animal products.
B12 is absorbed in the ileum, the very last part of the small intestine. Most everything else is absorbed before that in earlier parts of the intestine. B12 combines with something called Intrinsic Factor in order to work. The stomach acid issues can affect the Intrinsic Factor availability too. Intrinsic Factor is necessary to bind with the B12 in the stomach to "protect" it in the upper small intestine and from the stomach acid. Then the Intrinsic Factor attaches to some receptors at the end of the small intestine in the ileum aiding the B12 uptake. So at times it is the Intrinsic Factor and the fact it cannot attach to the receptors to facilitate transport and absorption into the body that is the problem and the cause of B12 deficiency. The sublingual B12 is highly preferred for this reason because it gets the B12 into the system and bypasses the entire Intrinsic Factor mechanism. (as you are taking now).
You can test methylation status through the use of a whole blood histamine test which is different from a plasma histamine test as I mentioned here
https://forums.phoenixrising.me/thr...ation-excess-of-methionine.90348/post-2438042 You can combine this with a homocysteine test to get additional info as this can be higher with lower folate or B12. Someone who has an SNP that might predispose them to impaired methylation does not mean they actually have impaired methylation. In fact, they could have completely normal methylation! On the other hand, a person who has no SNPs in their methylation genes could have severe methylation imbalance and may therefore benefit from some treatment but usually only when something is far too much in one direction causing health issues.
I look forward to hearing more, and perhaps get some feedback on my own experimentation.