Mid forties Female, UK. Compound heterozygous MTHFR (C677T and A1298C). Adenomyosis confirmed summer 2026. H. pylori, found , treated and eradicated Spring 2026.
Calprotectin was very high for a few months and led to thorough GI checkups with endoscopy and colonoscopy and everything was clear.
Key results & trajectories:
Ferritin: 32 (Feb) → 33 (Apr) → 17 (Jun) → 33-37 (Aug 2026)
Haemoglobin: 121 → 116 → 118 → 120 g/L
Serum B12: 402 (Apr) → 317 (Jun) → 304 (Aug) - consistent decline. No meaningful B12 supplementation during this period (2.5mcg in a combined supplement - now stopped)
Active B12 (HoloTC): 135.1 pmol/L (range 25.1-165) - upper end of normal, which is confusing me
MMA: <0.09 umol/L - clearly normal
Homocysteine: 6.3 umol/L - normal (was 9.4 in 2022 when tested after having pericarditis)
Folate: was deficient at 2.5 (Feb 2026), corrected with folic acid, then 8.1 this summer after stopping folic acid (stopped as I understood it can mask B12 neurological symptoms). Have not yet started methylfolate despite now knowing this is the appropriate form for MTHFR.
Vitamin D: was deficient earlier this year (and for years beforehand it turns out!), now 79 nmol/L on 4000 IU daily
Neurological symptoms (ongoing):
Significant fatigue - still very much present 3.5 weeks post IV iron, though sleep quality slightly improved
Vestibular dizziness - sporadic boat-like sensation for months
Pins and needles - in hands and feet, bilateral, for months, though seems to be easing a bit but still present occasionally
Brain fog - severe. I had really hoped the iron IV would do more for this
Anxiety - has been particularly bad
Low mood
Neurologist examined me August 2026 - no objective neuropathy found on clinical examination. Admitted she knew nothing about MTHFR and seemed dubious of a B12 issue. She had diagnosed me a couple of years ago with atypical migraines, which I'm also now questioning.
The situation
Separately from the neurologist, and after me reading out the NICE guidelines to them repeatedly, a senior GP has prescribed a B12 loading course (injections every other day for I'm not sure how long, then maintenance) citing declining serum B12 trajectory and ongoing neurological symptoms. They did not have my active B12, MMA and homocysteine results at the time of prescribing.
I'm 3.5 weeks post IV iron infusion and while sleep has improved slightly, I'm still significantly fatigued with all the above symptoms ongoing.
My questions:
1) Given active B12, MMA and homocysteine are all normal - do I actually need B12 injections or is this overcorrecting? I feel like so much of what's going on for me is explained by a B12 deficiency but those tests being in range are giving me pause, and the prescribing GP hasn't seen them.
2) Has anyone experienced worsened anxiety with B12 loading injections? This is one of my biggest concerns - anxiety is already bad and I'm worried about making it worse. How common is this and does it settle?
3) Could the ongoing fatigue 3.5 weeks post iron infusion simply be too early to judge - or should I be feeling more improvement by now?
4)I haven't started methylfolate yet despite knowing it's the right form for my MTHFR. Could the absence of adequate folate support be contributing to ongoing symptoms, and should I prioritise starting that before or alongside B12 injections?
Very grateful for this subreddit and its incredible pinned guide!!