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 Vitamin B12 deficiency symptoms: A metallic taste in your mouth could be a sign Express.co.uk Vitamin B12 deficiency symptoms: Metallic taste in your mouth can mean you're lacking B12 Express.co.uk Vitamin B12 Oral vs Injection