Vitamin B12 deficiency symptoms that show up in your mouth The Mirror What is that metallic taste in my mouth? The Wellness Corner A metallic taste in your mouth can be a sign of conditions ranging from gingivitis and pregnancy to dementia and kidney failure. What to know: Vitamin B12 is essential for healthy oral tissues. Its deficiency can affect the mouth early.., Oral effects , red,smooth,painful tongue(glossitis), recurrent mouth ulcers , burning mouth