I had a very red, sore tongue for over a year. Went to an ENT who tried antibiotics & also zinc. Nothing helped. I eventually had a spectracell blood analysis done to determine what vitamins I was deficient in, although this was done for general health and not related to the sore tongue issue. As it turned out I was deficient in 5 vitamins including folate. When reading up on the symptoms of folate deficiency I was surprised to see sore tongue as one of them. After taking folate for just a few days the red, tender tongue was cured. I was also deficient in B12 which I see others have indicated might be involved w/ sore tongue issues. Hope this helps someone out there!