International Agency for Research on Cancer (IARC) - Summaries & Evaluations


VOL.: 40 (1986) (p. 47)

5. Summary of Data Reported and Evaluation

5.1 Exposure

Human exposure to bracken fern and its constituents occurs by direct ingestion of the fronds in some regions of the world, or by ingestion of dairy products from cattle grazing on the fern. In the past, bracken has found other end uses such as in bread flour and medicinals.

5.2 Experimental data

Bracken fern was tested for carcinogenicity by oral administration to mice, rats, guinea pigs, cows and toads. In all species except cows, bracken fern induced malignant or benign and malignant intestinal tumours, particularly in the small intestine. It also induced bladder carcinomas in rats, guinea-pigs and cows, liver tumours in toads, lymphocytic leukaemias in mice and mammary cancers in rats.

Administration in the diet to rats of bracken fern that had been processed as for human consumption produced intestinal tumours, but at a lower incidence than unprocessed bracken fern.

In one study in rats, starch made from bracken fern rhizomes did not produce tumours.

Oral administration of boiling-water extracts of bracken fern to rats induced intestinal and bladder tumours; administration of ethanol extracts to quails produced intestinal tumours.

In studies on the carcinogenicity of substances isolated from bracken fern, oral administration of ptaquiloside to rats produced mammary and intestinal tumours. Shikimic acid has not been adequately studied. Kaempferol, quercetin and tannins, which also occur in bracken fern, were evaluated in previous volumes of IARC Monographs.

Administration of bracken fern in the diet in one study in mice at one dose induced maternal toxicity, some embryotoxicity and some minor abnormalities in offspring.

An acetone exact of bracken fern was mutagenic to Salmonella typhimurium in the presence of an ogenous metabolic system; light petroleum and methanol extracts of bracken fern activated by alkaline treatment were mutagenic to S. typhimurium in the absence of an exogenous metabolic system.

Ptaquiloside induced unscheduled DNA synthesis in primary rat liver hepatocytes.

Shikimic acid was not mutagenic in Salmonella typhimurium. It did not induce chromosomal aberrations in cultured Chinese hamster cells. Conflicting results were reported in the dominant lethal test and negative results in the heritable translocation test in mice.

5.3 Human data

One case-control study from Japan has suggested an association between intake of bracken fern and cancer of the oesophagus.

5.4 Evaluation

There is sufficient evidence for the carcinogenicity of bracken fern in experimental animals.

There is limited evidence for the carcinogenicity of ptaquiloside derived from bracken fern in experimental animals.

There is inadequate evidence for the carcinogenicity of shikimic acid derived from bracken fern in experimental animals.

There is inadequate evidence for the carcinogenicity of bracken fern to humans.

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Suppl. 7 (1987)

Last updated: 22 April 1998

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