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Toxicity of Bracken Fern
Spotted Wing Drosophila Study

Toxicity of Bracken Fern

I noticed in the March-May 2013 Vol. 41, Number 1 issue on page 24 Chris Knapp's article on Spring Wild Greens, encouraging the consumption of bracken fern, Pteridium aquilinum. Numerous studies have shown bracken fern to be carcinogenic to mammals. Would you please make sure that a correction is printed in the next edition of The Maine Organic Farmer and Gardener or by electronic means?

Best regards, 
- David Fuller, Agriculture and Non-Timber Forest Products Professional, University of Maine Cooperative Extension, Farmington


This article described boiled bracken fern fiddleheads (immature fronds) as an edible spring green, with the boiling water discarded.

Bracken contains numerous secondary metabolites, including one called ptaquiloside, which is known to cause serious disease in animals that graze on the raw fern, from thiamine deficiency to cancer. Ptaquiloside is very soluble in water, so foragers who recommend eating bracken say to boil the fiddleheads one or more times and discard the water before consumption. Supporting this recommendation is work by Saito et al. (see references, below), who found that the ptaquiloside content in some commercial bracken products from Siberia and Japan was below the limit of detection.

Most feeding studies on the toxicity of ptaquiloside have been done with raw or dried bracken or with aqueous extracts that contain the water-soluble ptaquiloside. One study, in which rats were fed such an extract for 54 days, found tumors in almost all treatment rats but none in control rats. The researchers concluded “that bracken carcinogens are partially extracted into water during cooking in the manner used in Brazil.”

Some of the few epidemiological studies done among cultures where bracken is commonly eaten have suggested an association with stomach, bladder and/or esophageal cancer, but these studies have been criticized as methodologically too weak to show a clear relationship. (Wilson et al.) Richard Philp says, “At one point, it was suggested that the relatively high incidence of bladder cancer in Japan might be related to consumption of bracken fern. Epidemiological studies, however, have failed to demonstrate such an association, and it is now felt that eating fiddleheads does not constitute a risk factor for cancer."

Brown et al. found that Vermont and New Hampshire residents who died during 1975–79 from bladder cancer were less likely to have consumed bracken than a control group. The authors say their results combined with those of a Canadian study show that “bracken poses no serious health threat to exposed populations.”

On the other hand, Recouso et al. found that human “habitual consumers” of bracken in Brazil had “increased levels of chromosomal abnormalities, such as chromatid breaks, in cultured peripheral lymphocytes…” compared with a control population.

Interestingly, because ptaquiloside is so water soluble, researchers are concerned about the potential effects on human health of ptaquiloside that leaches from fern fronds during rains and may contaminate drinking water, as well as ptaquiloside in milk from animals that graze on raw bracken, and in meat of animals that graze on bracken. Airborne spores from the fern also contain ptaquiloside.

The best, most recent review I know of is Ramwell’s May 2010 report, which says, in relation to toxicity to humans, “The published literature on the toxicity of bracken fern and its constituents was extensive, but many of the studies were old, and few of them were up to modern standards.” Rasmussen’s 2003 Ph.D. thesis also offers in-depth information, as does a 2008 U.K. draft report at http://cot.food.gov.uk/pdfs/TOX200830.pdf.

“I guess the bottom line on the consumption of brackens,” says David Fuller, “is that they may pose a health risk (cancer) and as such should not be eaten. There are too many healthy alternatives.”

Lebelle Hicks, toxicologist with the Maine Board of Pesticides Control, agrees with Fuller. She cites Cáceres-Peña et al., 2012, showing that cooking reduced but did not eliminate ptaquiloside and other compounds.

If the conflicting reports in the literature – combined with the fact that bracken fern contains other secondary metabolites that have not been thoroughly studied and that may promote or fight cancer – leave you scratching your head, you might want to stick to eating fiddleheads from the ostrich fern, Matteuccia struthiopteris – although UMaine Cooperative Extension recommends that with these, too, consumers take care, as “a number of outbreaks of foodborne illness associated with the consumption of raw or lightly cooked fiddleheads” have occurred (http://umaine.edu/publications/4198e/).

Brown, L. et al, 1999, “Bracken fern consumption and human bladder cancer,” J. Epidemiol Community Health, Oct;53(10):653, www.ncbi.nlm.nih.gov/pmc/articles/PMC1756788/pdf/v053p00653.pdf

Cáceres-Peña, Yamile C., et al., "Influence of Bracken Fern (Pteridium caudatum L. Maxon) Pre-treatment on Extraction Yield of Illudane Glycosides and Pterosins," Phytochemical Analysis, Nov. 20, 2012, http://onlinelibrary.wiley.com/doi/10.1002/pca.2409/abstract

Philp, Richard, Ecosystems and Human Health, CRC Press, 2001

Ramwell, C.T. et al., “Ptaquiloside & other bracken toxins: A preliminary risk assessment,” May 2010, report for The Food and Environment Research Agency, York, U.K., www.academia.edu/2864499/Ptaquiloside_and_other_bracken_toxins_A_preliminary_risk_assessment

Rasmussen, Lars Holm, 2003 Ph.D. thesis, “Ptaquiloside – An Environmental Hazard?” Ph.D. thesis, 2003, at http://curis.ku.dk/ws/files/13012945/Lars_Holm_Rasmussen.pdf

Recouso, R.C. et al., 2003, “Clastogenic effect of bracken fern (Pteridium aquilinum v. arachnoideum) diet in peripheral lymphocytes of human consumers: preliminary data”, Vet. Comparative Oncol., 1(1): 22-29. www.ncbi.nlm.nih.gov/pubmed/19379327

Satio et al., 1989, “Chemical assay of ptaquiloside, the carcinogen of Pteridium aquilinum, and the distribution of related compounds in the Pteridaceae,” Phytochemistry 28, 1605-1611)

Santos, R.C. et al., 1992, Tumorigenicity of boiling water extract of bracken fern (Pteridium aquilinum (L.) Kuhn.), Ciencia e Tecnologia de Alimentos; Vol. 12 (1), 1992, 72-76.

Wilson, D. et al., “Should we be frightened of bracken? A review of the evidence,” J. Epidemiol. Community Health. 1998 Dec;52(12):812-7. www.ncbi.nlm.nih.gov/pubmed/10396523

– J E


Spotted Wing Drosophila Study

After harvesting a nice crop of wild organic blueberries this past summer, I was intrigued by reports in the media of alarming infestations of spotted wing drosophila (SWD) in various soft fruits, including blueberries. Not having noticed anything unusual in the 60 acres or so that we harvested in five counties, I decided to phone all 50 of the MOFGA-certified blueberry growers to get their observations.

Thirty-five of the 50 are lowbush (wild) growers. A few had put out insect traps at the suggestion of Extension or UMaine people. All but one of the traps yielded SWD, anywhere from one to hundreds. However, none of the 35 reported damage to their crops or complaints from customers.

Fifteen growers had highbush (cultivated) blueberries. Several used traps and found SWD. Three growers observed significant damage to their crops, especially after August 20. One responded with MOFGA-approved insecticide every two days. However, the expense of such treatment makes the future profitability of that operation doubtful.

During the survey I also ran into two conventional highbush growers, both of whom reported substantial damage – in Turner and Athens. Both habitually used synthetic ammonium fertilizer.

– Arthur Harvey, Hartford, Maine



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