Vitamin B12 activity in comfrey (Symphytum sp.) and comfrey products
Briggs, D.R.; Ryan, K.F.; Bell, H.L.
Journal of Plant Foods 5(3): 143-147
Very low levels of activity were found in leaves, roots and stems of Symphytum officinale and in comfrey teas and tablets. Relatively large amounts of these products would need to be consumed to contribute significantly to dietary intake of vitamin B12.