This information is absolutely the opposite advice that should be given, all based on antiquated info from the Walsh/Pfieffer Clinic from the 1970's and early 1980's. They used folic acid for pete's sake, something that BLOCKS methylation, instead of the natural folates like methylfolate and folinic acid.
Methionine doesn't provide ANY methyl groups to lower histamine levels, nor does calcium or b6 -- just ridiculous and dangerous information.
Histamine is lowered w/methylfolate, methylb12, and also via the diamine oxidase enzyme, which requires copper and b6.