Hi,
I have read your question and would be pleased to answer your question.
you develop
vitamin B12 deficiency if you are vegetarian or on vegan diet and have conditions like
pernicious anemia or
gastritis and others which interfere with the absorption of vitamin B12.
since our body does not make vit:B12 naturally, you have to get it through animal food sources like fish, meat, eggs, vitamin B12 fortified foods and supplements.
It takes times for your body to come in balance with vitamin B12 usually few weeks to months and for symptoms to go away if you are taking
vitamin B12 supplement in injection or in oral supplement form.
your doctor first would give you supplement shots and then gradually will bring you on high dose oral supplement once it comes to normal and as symptoms go away your doctor might advise you low dose supplement to prevent develop vitamin B12 deficiency again.
If you are vegetarian , you can prevent deficiency by switching to animal diet and may not need to take supplements.
If you have medical cause it needs to be treated.
Hope this answer is helpful.
Thanks
Dr.Pari