Ferns rank among the world's most widely distributed plants, found across several continents. In China, they grow extensively with numerous varieties, and their tender shoots are commonly consumed as vegetables in many regions. Residents of certain areas habitually use bracken ferns as a vegetable.During the Ming Dynasty, Luo Yonggong described bracken thus: "Piled on plates, steamed purple agate; chewed in the mouth, clear glass. Melting and swaying, sweet as honey; hunger vanishes, spring returns to the belly." This captures bracken's appealing color, aroma, and taste. However, modern research indicates that this "king of wild vegetables" carries cancer risks.Consider the following five sets of data:
1. Over a century ago, it was observed that bracken could poison cattle. Cattle consuming large quantities of young shoots could die within weeks. Those eating smaller amounts gradually lost bone marrow function, leading to symptoms like leukopenia, thrombocytopenia, and acute hemorrhage. Sheep consuming bracken gradually lost their sight.
2. These phenomena gradually piqued scientists' interest. By the 1960s, research confirmed bracken's carcinogenic effects. A 1970s study in Japan's central mountains investigated the link between bracken consumption and esophageal cancer. It found that among local residents, bracken consumption increased esophageal cancer rates by 2.1 times in men and 3.7 times in women.
3. In North Wales, UK, stomach cancer rates have long been elevated. A 1990 case-control study similarly demonstrated that consuming bracken fern in childhood increases the risk of developing stomach cancer later in life. Similar studies conducted elsewhere in the world yielded largely consistent results.Animal experiments using cattle, rats, sheep, and quail induced tumors in up to 79% of cases. Subsequent research indicated that bracken fern not only directly causes cancer but also promotes and synergizes the growth of existing cancers. When scientists processed bracken fern using methods mimicking human consumption and fed it to animals, it still induced intestinal and bladder tumors, albeit with a longer latency period and lower incidence rate.
5. Experiments with cow's milk revealed that milk from cows fed bracken contained carcinogens. Consequently, small animals fed this milk developed cancers of the intestine, kidneys, and bladder. Direct human consumption of such milk would also pose a carcinogenic risk. However, raw milk is rarely consumed; milk for human consumption typically undergoes high-temperature pasteurization, significantly reducing its carcinogenic potential.
So what substance in bracken fern possesses such potent carcinogenicity?
After over two decades of relentless effort, Japanese scientists successfully isolated a compound called "pteridinone" in the early 1980s. Pteridinone is present in the roots, stems, and leaves of bracken fern, with the highest concentration found in the tender shoots.Subsequent animal experiments using pteridinone confirmed its ability to induce the aforementioned symptoms and diseases.
Scientific research has demonstrated that bracken fern contains cancer-related substances including pteridine, pteridinol, xanthine alcohol compounds, pteridinol, and pteridinol-like substances, all linked to gastrointestinal carcinomas.
Of course, eating bracken fern once or twice won't immediately cause cancer—this depends on the amount of carcinogens ingested. However, long-term consumption of bracken fern can pose health risks.Those who have frequently consumed it in the past need not panic, as the typical processing method involves blanching before eating. This treatment significantly reduces the original content of pteridinone glycosides. However, it only reduces, not eliminates, these compounds. With long-term consumption, pteridinone glycosides can still accumulate in the body. Therefore, while bracken fern may be delicious, it's best to steer clear.