Comfrey and its bone-setting properties

Recent warm weather has resulted in the earlier than usual appearance of the nodding, bell-shaped flowers of the common comfrey, Symphytum officinale.

The flowers may be white, cream, pink or purple, but are always the same colour on any one plant.

The species is widespread throughout England and Southern Scotland, growing in damp places.

Medieval herbalists used comfrey for bone setting. The roots were dug up in spring and grated to produce a sludge, which was packed around the broken limb. This hardened to a consistency similar to that of plaster of Paris.

Regional names for the plant reflect its former use, such as knitbone and boneset. The common name is said to be derived from the Latin conferre, “to bring together”.

More recent research has suggested that as well as acting to immobilise the broken limb, comfrey also contains allantoin, a compound renowned for its ability to promote cell growth as well inhibiting infection. It has been postulated that this may have an effect on generating bone and tendon growth.

Comfrey was traditionally taken as an infusion, with the leaves in particular being infused in hot water. There is evidence that aqueous extract of comfrey inhibits prostaglandin biosynthesis, resulting in an anti-inflammatory and analgesic action.

Other research has shown components of comfrey to have cholinergic activity and the ability to inhibit tumours. Indeed, one pyrrolizidine alkaloid, indicine, has been investigated as a possible chemotherapeutic agent.

A 2005 study in Seattle compared the effectiveness of comfrey cream with diclofenac gel in treating ankle sprains. The preparations were applied four times a day for one week, and it was found that the group using comfrey had significantly greater alleviation of pain and swelling.

It was also found that the comfrey group reported faster and more complete recovery than the other group.

A major drawback with comfrey is the presence of pyrrolizidine alkaloids. The alkaloids are metabolised by the liver to pyrroles, which exert their toxic effect by reacting with cellular macromolecules, including proteins and DNA, causing hepatic tissue changes.

Studies have shown that topical application, however, results in alkaloid urine levels approximately 20 times less than that with oral administration, and there has been no evidence of hepatic damage resulting from topical administration.