PA is an autoimmune condition that causes B12 deficiency.
The symptoms of folate deficiency and B12 deficiency overlap a lot because the two are used together for a lot of processes in the body so those processes stop working properly if there isn't enough B12, or there isn't enough folate, or there isn't enough of both.
One classic symptomit of B12 deficiency is macrocytic anaemia - in which red blood cells are larger and rounder than normal. This is also caused by folate deficiency. Address the deficiency/deficiencies and it will be corrected.
High dose folic acid will correct a folate deficiency but it won't resolve the problem that caused you to be folate deficient in the first place. To stop the deficiency recurring you would need to address that. This could be lack of folate in your diet or it could be an absorption problem so next question is what is your diet like in terms of folate? If it was low in folate (found in vegetables - particularly green leafy vegetables) then you obviously need to address that. If your diet is already rich in folate then the problem is absorption - some absorption problems are treatable - others aren't so next step would be to try and determine cause of the absorption problem .... and keep supplementing with folate whilst this is happening - treat if treatable and then you should be able to get enough from your diet. If the absorption problem isn't treatable then you will need to continue supplementing - though you won't need doses that are as high as those that are being used to treat the deficiency.
Absorption problems can be caused by PA, Ceoliacs, Crohn's, general lowering of stomach acidity as you get older, drug interactions (eg PPIs), h pylori infection and there will be others.
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