800iu of vitamin D won't help raise a deficit very quickly. You need to aim for a level around 100nmol. As your wife is not severely deficient, she may have to buy her own Vitamin D3 supplements to add to the 800iu already taken.
The vitamin D Council gives some advice about levels to supplement if your GP cannot prescribe sufficient amounts of vitamin D3.
You may wish to take magnesium and K2-MK7 with vitamin D3 in order to absorb the vitamin D effectively. Magnesium citrate is ok but there are other choices for magnesium.
Have you got symptoms of B12 deficiency because if so, I advise you to post your B12 and folate results along with an outline of your thyroid condition and symptoms, low ferritin etc on the HealthUnlocked Pernicious Anaemia forum healthunlocked.com/pasoc and ask their advice about what your GP should be doing. Really, it looks like you need further investigations to rule out pernicious anaemia. Your GP should check for intrinsic factor antibodies.
Oh, I see now your wife is being treated for B12 deficiency so folate supplements alongside are ok I believe. Find out about B vitamins from the pernicious anaemia HealthUnlocked forum.
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