What Causes Numb Taste Buds?

my husband ,aged 85, complains of a loss of taste whatever he eats. What health conditions could cause this? He has spoken to his doctor about his meds including supplements such as Omega Q Plus made by Dr. Sinatra. Any information would be appreciated. Tests for B12 Vitamin D have been done and the excess of B12 could be the culprit. He has been off all supplements for 2 or 3 weeks but sees no improvement.Thank you